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Hit So Hard, the Calendar Felt It

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It's The End of the World as We Know It, and The End of the Beginning as well. Either the few remnants of sentient life (we're talking either Class 1 or 2 here) are rebuilding, or some reality-altering event has taken place which reshapes their entire conception of history. In any case, they see fit to reset the calendar and set civilization's New Beginning as Year Zero (or year one).

Can also be revealed to have happened in retrospect as a Worldbuilding trope — the event after which a society dates its calendar tells you something about their culture.

Multiple science fiction stories in the 1950s and 60s postulated that at some unspecified point in the future, mankind would reset the calendar to start with the detonation of the first nuclear warhead as year one. This went out of fashion rather quickly as soon as the dangers of fallout became widely known.

Not to be confused with people being "punched into next week."


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    Anime & Manga 
  • Some unknown event caused the calendar to reset in Attack on Titan over 850 years ago. Oddly this doesn't match up to when the titular titans appeared or when they they built the walls that protect the last vestige of humanity.
  • The setting of Battle Angel Alita: Last Order marks time according to the Era Sputnik, counting from the launch of the Sputnik 1 in 1957. The story also informally refers to years in the "Anno Koyomi" — because the background character Koyomi, was born the same year that the series began with Alita's rebirth.
  • Nobody remembers what year it is in The Big O because everyone was hit with Laser-Guided Amnesia forty years ago. As a result, people tend to refer to the date by referencing the loss of memory "X years ago".
  • One of the proofs that the Holy Britannian Empire is the most dominant force on Earth in Code Geass universe, the calendar doesn't follow the real world AD/CE - instead, we have A.T.B, for "Ascension to Throne, Britannia", counting from the establishment of the first Celtic King in the Britannian royal line, rather than the birth of Christ. (For those wondering, 1 A.T.B. - 50 B.C., which means the series is set in an alternate 1967/68.) Closer to this trope is the Revolutionary Calendar used by the EU, a variant of the French Republican Calendar that sets its first year to 1790, the year after the French Revolution.
  • The calendar was reset at some point in From the New World, due to the long dark ages of mass slaughtering by psychics. They're currently in the 200s. It actually seems to have been running for roughly the length of Tomiko's life, and may have been reset again because of K's rampage. There doesn't seem to be much communication between distant villages, either, so they may all be using different calendars.
  • Fullmetal Alchemist (2003) once used a different dating system for years, but this ended about the time alchemy rose to prominence. Since the 2003 anime is based in an Alternate Earth, years were at one point measured in the Anno Domini system, but this faded away at the same time Christianity did.
  • The Gundam franchise loves using alternate calendar systems, but the only one that really matches this trope is Gundam X, which is set in After War 0015, 15 years after the disastrous end of the 7th Space War which wiped out 99% of humanity living on Earth. Some fan theories suggest that Gundam Wing's After Colony calendar started with the launch of Skylab, but there isn't any official proof that this is true or not. Special mention to ∀ Gundam, which implicitly has several dozen calendar changes in its backstory, to the point where this trope is the only explanation. Every single timeline will eventually have a version of the Turn A, which inexplicably causes a timeline reset into a new alternate universe through massive destruction.
    • Some Gundam universes have more concrete explanations. The Future Century of G Gundam is based on the establishment of the world government that currently oversees international affairs as well as calls for the Gundam Fight every four years to determine which Neo Nation has ruling power for the interim. This after apparently lots of brutal fighting finally brought those countries to the peace table to hammer out some way to institutionalize their constant conflicts. The series takes place throughout the year FC60, which is marked as the year of the 13th Gundam Fight. (The backstory establishes that the first Gundam Fight was in FC8, and the 12th Fight was postponed four years over the tensions that arose after Gentle Chapman's third consecutive victory for Neo England.)
    • Mobile Suit Gundam 00 sticks with Anno Domini instead.
    • Gundam: Reconguista in G uses Reguild Century, in which the backstory vaguely mentions cataclysmic wars, environmental disasters and famines so severe people had to resort to institutionalized cannibalism in the final moments of the Universal Century calendar.
    • Speaking of the Universal Century, Mobile Suit Gundam Unicorn reveals that the calendar change occurred on the eve of the United Nations' reformation into the Earth Federation, which was supposed to be peaceful... were it not for a Government Conspiracy blowing up the Laplace space station where the first Prime Minister of the Federation was holding his inauguration speech, an event whose aftershocks shaped world history for the next hundred years.
    • Mobile Suit Gundam: Iron-Blooded Orphans uses the Post Disaster calendar, with Year 000 being the conclusion of the Calamity War. The series takes place in PD 323.
  • In Lyrical Nanoha, the new Mid-Childan calendar begins after the Ancient Belka War, which ended when the dominant Ancient Belka Empire destroyed itself and rendered their planet uninhabitable due to a combination of infighting and the Lensman Arms Race, leading to the banning of mass-based weapons on all dimensions.
  • At some time, possibly after the War with Them, the Sound of the Sky calendar was changed to A.P.
  • Yuki Yuna is a Hero is set in the Year 300 of the Divine Era. The prequel light novel, Nogi Wakaba Is a Hero, tells the story of the end of the Anno Domini Era. The Divine Era begins after the last vestige of humanity agrees to give up the divine weapons bestowed on them by the Shinju-sama in return for a cease-fire with the Celestial Gods who are trying to wipe out humanity. As it turns out, the Taisha secretly broke the agreement and continued to develop the Hero System, leading to the events of Washio Sumi Is a Hero and Yuki Yuna Is a Hero.

    Comic Books 
  • Transmetropolitan takes place at some unspecified year in the future. No one ever refers to a specific year; it's always in reference to other events. At one point, we're told that a Revival truly lost it when she asked what year it was, and "they told her." It's not stated outright, but what they probably said was "we have no idea."
  • The Marvel 2099 seen in Timestorm 2009-2099 includes a brief scene set some years earlier with a holographic teacher modeled on Reed Richards explaining that it probably isn't really 2085 because they started counting again from the last date before the disaster.
  • The Hypernaturals by Dan Abnett and Andy Lanning is set in the year 100 AQ (Anno Quantinuum), a century after The Singularity.

    Fan Works 
  • Half Past Adventure features a somewhat less apocalyptic version of this where the new calendar's year zero is the Adventure Time seasons finale.
  • The propensity for this in The Silmarillion is referenced in the abridgement The Entire Silmarillion of J. R. R. Tolkien in One Thousand Words:
    Gondorians: *change calendar*
  • In Pokémon Reset Bloodlines, Professor Oak's research in making wild Pokémon less aggressive was very important to society. In fact, it was so important that when he succeeded in his endeavor (around forty years ago), it was dubbed the start of the Oak Era.
  • In With Strings Attached, the planet C'hou underwent some kind of big shakeup about five hundred years previously. Among other things, it seems to have removed all concept of calendars and clocks from Baravada.
  • In Enlightenments, Wander asks what year it is at one point. Dormin, an extremely old deity who has seen more than their fair share of mortal calendar systems, responds by asking him "by whose count?" Wander settles on essentially asking for the regnal year of the Queen of the Castle in the Mist (making it Year 365 by that count, for the curious).
  • In A Thing of Vikings, the new Norse calender has the year zero corispond to 1044 on the Christan Calendar. 1044 is the year that Norse holy texts get published making the beging of the Norse Reformation in the story.

    Films — Animation 
  • Titan A.E.: The movie begins A.D. 3028 and ends 15 years later, in the year 15 A.E. (After Earth).

    Films — Live-Action 
  • In 2012, the surviving humans reset the calendar after the Cataclysm.
  • Similarly, in Cloud Atlas (both the book and the movie) some of the events take place 106 years After The Fall. What exactly was the Fall is never explained, though.
  • In the '50s movie When Worlds Collide, a rogue planet passes by Earth and destroys it due to tidal effects, but the passing planet itself is inhabitable. In the end, a few people land on it to repopulate it, and an ominous Bible-like title card says this is Year One.
  • In Land of the Blind, the calendar is reset with the year of the revolution as Year Zero. The film begins in Year Minus Five.
  • The film Panic in Year Zero! gets its title from the decision of the United Nations to reset the calendar after World War III went off-the Title Drop is a declaration heard by the main characters on an update broadcasted through the CONELRAD emergency broadcast system.
  • In Star Wars, the calendar was reset to 0 after the destruction of the Death Star, with dates either being labeled with BBY (Before the Battle of Yavin) or ABY (After). This, however, only applies to the Expanded Universe, and is never mentioned in the films themselves. The calendar reset was only applied after the Galactic Civil War ended, by which time a second Death Star had also been destroyed.
  • Pacific Rim gives the date of the battle between Knifehead and Gipsy Danger as "Kaiju War, Year 6". Background material says the war began in 2013.

  • In the world of Lone Wolf, Magnamund's calendar is based around the date of creation of the Moonstone (the ultimate artifact of good) by the Shianti (a race of demigods).

  • Edgar Pangborn's Davy and related stories take place in North America centuries after a 'limited' nuclear and biological war. Some years after the war a prophet named Abraham arose, and the church founded on his martyrdom established a new calendar from that date, with The Year of Abraham replacing Anno Domini.
  • The Dune books did something analogous, resetting the calendar when the Spacing Guild established its monopoly (which was about 108 years after what might have been regarded as the "apocalypse" — the end of the Butlerian Jihad). Many people misinterpret the series' start in the Year 10,191 (A.G. — After Guild monopoly) as Anno Domini (A.D.) because the latter was used in the introduction scene of the David Lynch film adaptation.
  • The Legend of Rah and the Muggles has the calendar being reset by a nuclear war. The problem is that they talk about the "year of the purple haze" [nuclear fallout]. Every single year in living memory has been the year of the purple haze!
  • Isaac Asimov's short story Living Space shows a society which has discovered travel between parallel Earths, mostly empty, which means that everyone can have a world of their own. Until they run into one populated by Germans who use a calendar starting from the birth of Adolf Hitler. note 
  • The Orphan Master's Son is set in North Korea, where the calendar is dated from the birth of Kim Il Sung in 1912 (see Real Life below).
  • In A Song of Ice and Fire (as well as Fire & Blood), the years are dated from the Targaryens' conquest of Westeros. This actually troubles maesters, as several years went by between the time Aegon declared himself King and his actual coronation in the Starry Sept of Oldtown.
  • In The Stand, Randall Flagg tells the date as "this thirtieth day of September, the year nineteen hundred and ninety, now known as The Year One, year of the plague."
  • Tolkien's Legendarium
    • Arda, Tolkien's world, uses two series of ages based on important events in history. First there is the Ainulindalë, the period before and during the creation of the world. The next, top-level ages are named after the methods the immortal Valar used to light the world. First are the Years of the Lamps. Once those are destroyed by Melkor, the calendar switches to the Years of the Trees. Finally, once those are destroyed (again by Melkor), they change to the current Years of the Sun.
    • Each of those ages is then further divided into ages of their own. These ages are used to count years by men and elves. The First Age of the Sun begins when the sun first rises and men are created, and ends after Melkor is finally defeated (as detailed in The Silmarillion). The Second Age lasts until Sauron is defeated (the first time) and his Ring is claimed by Isildur. The Third Age, which The Hobbit and The Lord of the Rings take place at the end of, ends when the ring-bearers leave Middle-earth after Sauron's final defeat, officially lasting 3021 years.
    • As Arda was intended to be Earth in the distant past, Tolkien had ideas about further ages. He estimated that the ages were getting shorter as time went on. Thus, 20th century Earth would be set in either the sixth or the seventh age. No times for when these ages changed over has ever been given, though.
    • On a smaller scale, though the Third Age continues for another two and a half years, Gondor under King Aragorn declares a new year to have begun on the day of the Ring's destruction (March 25, Third Age 3019) and dates its own calendar from that point going forward.
  • The Turner Diaries is set in 1991 and 1993. During the epilogue, it is explained that around the year 2000, they reset the year to coincide with the annihilation of all minorities.
  • In the Eighth Doctor Adventures novel "Reckless Engineering", the year 2003 has become the year 160 following the Cleansing, a devastating event in 1843 when Time mysteriously accelerated across several dimensions, causing every living thing on Earth to age forty years in seconds. As a result, all adults and most animals withered and aged, children grew to adulthood almost at once, and the babies and other children under five years old who found themselves in adult bodies became capable only of breeding and feeding, with their descendants now being known as the Wilde Kinder, or Wildren, subhuman cannibals little better than animals. When the Doctor arrives in this reality, humanity has regressed to more primitive dwellings with most groups restricted to vegetarianism due to the lack of any alternative source of food, society having turned to religion to explain such a devastating event as God's will as the human race was 'reborn in innocence'.
  • In The Wheel of Time, the historical records show several calendars being used. This has happened 3 times in recorded history: The end of the 2nd Age and the Breaking of the World, the Trolloc Wars, and the Hundred Years War. The story occurs at the end of the 3rd Age, so the calendar is likely to reset again.
  • In Charles Stross' novel Scratch Monkey, by the time of the book's setting (several thousand years from now), there have been so many rulers declaring new eras and new calendars that "Year Zero Man" has become the standard term for a totalitarian dictator.
  • In Tamora Pierce's Tortall Universe, the numbers of the years are followed by "H.E.", short for "Human Era" — the time after the Immortals were banished to the Realms of the Gods.
    • In her Circleverse, the years are dated "K.F.", counting "after the fall of the Kurchal Empire".
  • In the Codex Alera series, it is eventually revealed that the calendar is reset by the events of the series.
  • The hyperconsumerist society in Brave New World worships Henry Ford, and dates its calendar from the release date of the Model T.
  • In The Belgariad and its sequel, The Mallorean, the calendar used dates the year 0 to be when the evil god Torak cracked the world. This particular calendar is referred to as the Alorn calendar, implying that other nations may have different systems.
    • The Tolnedrans at least are implied to date by dynasty.
    • The Dals measured time in "Ages", which only ended when something momentous to their grand mission occurred. The cracking of the world corresponded to the end of their First Age, and the books take place in their Fifth Age.
  • The Mortal Engines quartet by Philip Reeve have all dates measured from TE - Traction Era, ie. the time from which cities started moving around gobbling each other up.
  • In Honor Harrington, there are numerous different calendars in use by humanity across the galaxy.
    • The galaxy at large uses the Ante/Post-Diaspora (AD/PD) calendar, which shifts the epoch to 2103 CE at the launch of the first colony ship, the Prometheus. The calendar measures time in T-years (Terra years) and T-centuries, but the months are unnamed. This is used for almost all communication between different star systems and practical planning and coordination.
    • Most planets have their own local calendars, based on the local year and usually dating from their founding. Manticore has the After Landing (AL) system, based on the arrival of the Jason in the Manticore Binary System and keyed to Manticore's orbit of 1.7333 Earth years to the year. This is primarily used for government work and official documentation.
    • Grayson is the only planet which still uses the pure Gregorian calendar with no local calendar at all. This calendar does not align with Grayson's orbit or seasons in the slightest, but they refuse to change. Their continued use of AD (Anno Domini) is also confusing for other people, as to the rest of the galaxy that means 'Ante-Diaspora'. The year 4000 AD for Grayson — the approximate time era of the series — reads as approximately six thousand years in the past for everybody else (2000 BCE as we currently measure it).
  • Riddley Walker uses the O.C. system, which stands for "Our Count."
  • Implied as Tally and Zane look at Rusty graffiti in the second book of the Uglies trilogy.
  • The far-future bits of the Enderverse (Speaker for the Dead, Xenocide, Children of the Mind, and some short stories) dates events from the foundation of Starways Congress, the interstellar pan-human government established 1180 years after Andrew "Ender" Wiggin defeated the Buggers (an event implied to occur sometime between the 24th and 27th centuries AD). Speaker for the Dead starts in the late 20th century SC.
  • H. Beam Piper's Terro-Human Future History used Atomic Era dating, with 1942 AD note  as Year 0.
  • Larry Niven's Svetz the Time Traveler use Atomic Era dating as well, with the same starting point.
  • Ian Stewart's Hoard of Mathematical Treasures includes a "Future History of Mathematics", which parodies the genuine "History of Mathematics" earlier. Towards the end (after 11828 AD) we get "0: Reformation of the calendar", but what caused this is unknown. (Although it does seem to occur shortly after human civilisation rebuilds itself from machine rule.)
  • In Murderess, the people of the parallel world Greywall'd count years since Signus' Fall. Lu, the protagonist, came from Earth, and is a bit surprised to hear it's not the year 2012...
  • In Robert Browning's poetic retelling of "The Pied Piper of Hamelin", the townspeople make a decree that every legal document should contain a reference to how many years it has been since the Piper took their children. There's a possible element of Truth in Television there, as the official town records of Hamelin contain an entry from 1384, saying: "It is 100 years since our children left."
  • S. M. Stirling's Emberverse, set after the laws of the universe are suddenly and inexplicably altered, features the "Change Year" at the beginning of each chapter.
  • In Star Wars Legends, time is divided into BBY and ABY, before and after the Battle of Yavin (in order to distinguish prequels from the original trilogy).
    • Legends gives at least two more times this happens prior to Yavin (namely, the respective foundings of the Republic and the Empire). Luke complains about it in The Thrawn Trilogy, as it makes reviewing historical records rather tedious.
    • Both Legends and the current Star Wars Expanded Universe give us a lot of various calendars, which when you're talking about a galaxy-wide civilization across over 35,000 years of history, millions of planets and quadrillions of beings, makes sense. You've got the Tho Yor Arrival calendar, dating from when the first arks brought the pilgrims to Tython that would eventually found the Jedi Knights roughly 35,000 years before the movies, then you've got the Republic Year calendar dating from when the Galactic Republic was founded (roughly 25,000 years before the movies), the Tapani Calendar (started roughly 12,000 years before the films, used in one sector dating to when settlers first arrived there, and using a different length of year localized to the area), the After the Treaty of Coruscant dating to the treaty that set in motion the events of the Star Wars: The Old Republic MMO, plus the Great Resynchronization calendar, an in-universe attempt to create a new standard calendar to cut through the variety of calendars in use (it puts Year Zero as 3 years before Episode I), and the Imperial Year dating to Palpatine's declaration of a New Order in Episode III, and lastly the Before the Battle of Yavin/After the Battle of Yavin calendar dating to the events of Star Wars: A New Hope, which is taking the calendar most widely used by fans and making it an in-universe calendar.note  It's a lot of systems, but it's a big galaxy with a lot of history.
  • Becomes a plot point in the later Safehold novels, when the main protagonists find out about the Archangels' promise to "return" in a thousand years. The Church of God Awaiting counts years from the end of the War Against the Fallen, not from the day humanity awakened on Safehold — so is the return scheduled for the year 915 (1000 years after the "Day of Creation"), or the year 1000?
  • Seveneves uses dates starting from the moment the "Agent" blew up the Moon. The story begins 20 Minutes into the Future (the ISS still exists but has a small centrifugal section and an attached asteroid) but no real-world year is ever stated.
  • The world of The Supernova Era starts numbering years from the titular supernova era rather than the birth of Christ. In the epilogue, it's mentioned that there is some debate as to whether the beginning should be the first sighting of the supernova, the death of the last adult, or the start of the Great Migration; majority opinion seems to favour the middle one.

    Live-Action TV 
  • Blake's 7 takes place in the third century of the second calendar. It's never explained why they stopped using the first calendar in canon, but it's likely that it has something to do with why everyone on Earth is living in domed and/or subterranean cities with going outside being illegal. (Not that there's any fallout or other environmental hazards out there or anything, at least not by the time of the pilot; the Terran Federation just finds it easier to keep the populace in line that way.)
  • Star Trek reckons dates in Stardates, which are supposed to be a unified system in a Federation where planets have different days and years, and where starships travel at relativistic speeds and can be affected by time dilation. Different eras of the Franchise define and use the Stardates in different ways.
    • In the original series, there was deliberately no continuity for Stardates between episodes so there would be no way to assign a corresponding real-life date to the time frame of an episode. The only rule was that they contain four digits followed by a decimal point, and that they had to be internally consistent within each episode. The pilot episode "Where No Man Has Gone Before" began on Stardate 1312.4 and the final episode "Turnabout Intruder" began on 5928.5.
    • The system was standardized for The Next Generation, with Stardates beginning with 41 (Representing 24th Century, season 1) followed by three digits. 41000 corresponded to Earth year 2364, and the second digit counted upwards for each new season to line up with the in-series calendar year. The other shows of the TNG era (Deep Space Nine, Voyager, and now Lower Decks) use the same system and continue counting from the same starting point.
    • 2009's Star Trek and all works based on this timeline use a third system, directly corresponding to the Gregorian Calendar, with four digits followed by a decimal. The four digits indicate the calendar year, while the decimal indicates the day number. Stardate 2258.42 is the forty-second day of 2258 (Thursday, February 11).

    Tabletop RPG 
  • The German RPG The Dark Eye had the main realm count the years by the current Emperor. By now reckoning has been changed (back) to the 'BF - Fall of Bosparan' reckoning, counting from the fall of the former empire. There are also numerous other calendars around in that world, counting from the first landing of gildenland settlers, the independence of countries, the threat of a catastrophe by a messenger of the gods to a city, and so on.
  • Years in Dragonlance are numbered from the Cataclysm.
  • Eclipse Phase uses AF (after the Fall), mostly as a way to avert Exty Years from Publication. ("The Fall" being when a bunch of crazy AIs nearly wiped humanity out.)
  • Exalted:
    • The main setting's calendar has gone through several iterations, with setting books pointedly avoiding giving specific timeframes for most of them in order to preserve Storyteller's freedom. It was initially measured in years pertaining to the Age of Man, when the Primordials were overthrown and the Solar Deliberative was established. When the Solar Deliberative fell during the Usurpation, the Shogunate fiddled with an alternate calendar. At least until the Great Contagion ruined that as well and the Scarlet Empress ended up unifying various daimyos into the Realm, which is why the calendar currently uses RY (Realm Year) to designate how many years it's been since she took the throne. The end result is a calendar system that says, "It has been X years since the last world-shaking cataclysm."
    • Autochtonia, being essentially a Planet Spaceship that left the world sometime during the Solar Deliberative, has its own calendar. It doesn't provide a specific reference for any calendar matchups with the main setting, but they have several thousands of years of uninterrupted timekeeping more than the Creation.
  • One of Forgotten Realms' several calendars is "Present Reckoning", started on Time of Troubles. This fact is mentioned only once in the 3rd Edition books and everything else from then on is only the standard Dales Reckoning.
  • In a fairly realistic fashion, the Greyhawk campaign setting actually has several calendars, most of which are associated with ancient and now-defunct civilizations. The "Common Year" calendar currently used by most of the Flanaess is based on the crowning of the first Overking of the Great Kingdom of Aerdy, which was the first major nation to emerge in the aftermath of what was a magical nuclear war that forced lots of people to migrate to new lands.
  • On Dominaria, the default world of Magic: The Gathering, most nations use the Argivian Reckoning calendar, which sets Year 0 at the year the Brothers, Urza and Mishra, were born (Urza on the first day of the year, Mishra on the last). They were the leaders of the opposing forces in the Brothers' War, which destroyed multiple kingdoms, wrecked the continent of Argoth, and ushered in the Ice Age.
  • First Edition Paranoia: Dates were sometimes in the form of "Year 214 of the Computer"; i.e. 214 years since the Big Whoops (destruction of world civilization) and the takeover of Alpha Complex by the Computer.
    • It became even weirder in later editions where it was implied that, due to some sort of glitch, EVERY year is "Year 214 of the Computer". Although anyone who pointed this out would be implying that the Computer is defective, which is, of course, treason. In the 2017 Kickstarter edition it is explicitly stated that the Computer decided every year should be 214.
  • Rifts's Post-Apocalypse calendar came about when enough people realized that they had enough time and energy left over from trying to survive after The End of the World as We Know It (two or three centuries after it actually happened) to care about trivial matters like what year it was. The P.A. calendar is distinctive to North America, specifically the Coalition States and the surrounding area however. Some nations that weathered the Great Cataclysm better, most notably the New German Republic, are still using the Gregorian Calendar.
  • Surprisingly averted in Warhammer 40,000, which still uses our current calendar without even a token epoch shift (the "40,000" in the name refers to the 41st Millennium, the closing years of which form the current setting). Though heavily modified (not only are date stamps decimal it also takes into account the uncertainty of timekeeping in the multistellar empire where warp travel does all kinds of screwy things to causality), it's still the good old Gregorian calendar based on the Earth year and the birth of Christ. Probably they still use it because it's one of the few things they've managed to keep from the Dark Age of Technology, Humanity's lost Golden Age.
    • Played straight in that most worlds completely lost contact with each other during a time known as the Age of Strife, and among other problems such as losing the knowledge and/or means to produce most high-tech equipment, developing completely different languages, or spending a few thousand years being the repeat targets of marauding Xenos, was the fact that most developed unique calendars. While some still maintain local, informal calendars - especially worlds whose year lengths differ drastically from Imperial norm - they're almost never brought up in fluff or official literature as having the official calendar override everything else is part of the Imperium's attempt to "unify" all Mankind.
    • Played straight in the Dark Imperium era. After the Primarch returned and took over the Imperium, he found out that not only had recent events caused a serious Timey-Wimey Ball effect on the last few centuries, ten thousand years of flawed record keeping and deliberate redactions meant that current date even on Terra itself had a margin of error of a thousand years in either direction. He ended up just giving up and declaring that the new calendar would start from when the new Warp Storm visible in the sky of every world first appeared there and count in local years. It's less precise and requires constant conversions, but it's a hell of a lot more accurate. For out of universe convenience, this method started on 000.M42, essentially making it so that each planet is able to give how long they spent subjectively in-between contacts with the nearest Imperial Astropathic office, who then inform the planet of what year it actually is.
  • Years in Pathfinder are typically given in Absalom Reckoning, which dates to the ascension of the god Aroden and the founding of Absalom. A point generally agreed to be when humanity truly started to recover from the age of darkness brought on by an asteroid impact.
    • Conversely, Starfinder uses After Gap, referring to a calamitous Gap in both historical records and the living memories of sufficiently long-lived beings, during which the planet Golarion (Pathfinder's primary setting) disappeared.
  • The Third Imperium in Traveller calls the year of its founding Year Zero. Given the Long Night that the Third Imperium ended, it seems appropriate. Local governments signaled their cooperation by accepting this calendar reform. The Solomani, being the elitists (and speciesists) they are, never formally adopted it and still use the Gregorian calendar.

    Video Games 
  • Referenced in Grand Theft Auto: San Andreas. When a guy called The Truth gets something CJ stole from a government base, he says, "They shall call this Year 0."
  • The Elder Scrolls series' timeline is divided into "Eras," which each beginning and ending due to major events.
    • The Dawn Era is Nirn's Time of Myths, where Mundus (the mortal plane) was still settling following the events of creation. The et'Ada ("original spirits") who participated in that creation walked the earth, with some further sacrificing themselves to become the "Earthbones," the laws of nature and physics that would allow for life, while others made children with one another, who would become the Ehlnofey, ancestors to all the mortal races of Nirn. The Dawn Era came to an end when Akatosh, the Dragon God of Time, established linear time as a concept.
    • The Merethic Era, the era of the Mer (or Elves), then followed. Fleeing some unrecorded threat to their ancient homeland of Aldmeris, the Aldmer (ancestors of the modern races of Mer, whose closest living relative is the Altmer,) came to the continent of Tamriel and established a new homeland in the Summerset Isles. Over time, typically due to religious differences, the other races of Mer (the Bosmer, Dunmer, Falmer, Ayleids, Orsimer, and Dwemer) all split off and settled different parts of Tamriel. The Merethic Era came to an end when the Camoran Dynasty was founded in Valenwood, forever after limiting the influence of the Altmer on their mainland brethren.
    • The 1st Era saw the human Atmorans of the northern continent of Atmora successfully invade Tamriel and establish the first major threat of Men to the races of Mer. The First (Alessian) and Second (Reman) Cyrodiilic Empires were rose and fell in this Era, with the 1st Era ending after the last of the Reman line was assassinated without an heir.
    • The 2nd Era saw the Akaviri Potentates rule for the first several centuries of the new Era in a continuation of the Second Empire until they too were assassinated. Tamriel experienced the "Interregnum," their own version of the Dark Ages where petty kingdoms fought in fruitless wars and Tamriel was under attack from all manners of threat, including both mundane and supernatural. The 2nd Era came to an end after Tiber Septim successfully completed his conquest of all of Tamriel, becoming the first person to ever succeed in this feat, establishing the Third Cyrodiilic Empire. The spin-off game Redguard and The Elder Scrolls Online take place during this Era.
    • The 3rd Era ran for the duration of the Septim Dynasty and is the time when each of the first four games in the main series are set (as well as the spinoff game, Battlespire). It came to an end at the conclusion of the Oblivion Crisis, which saw the last of the Septim line die without an heir.
    • The 4th Era is the current Era of the series as of Skyrim. The Third Cyrodiilic Empire is in dire straights as internal strife, the Aldmeri Dominion, and the return of the dragons all stand against it as major threats.
  • Both Xenogears and Xenosaga share the same in-universe calendar "Transcend Christ." It is identical to the Gregorian calendar, but it reset the year numbers so that AD 2510 is year one. A short time after the new calendar is chosen, humanity leaves Earth.
  • In the Star Ocean games, the calendar was reset in 2091 so that 2087, the year of the invention of the first FTL engine, was year one. Dates are marked as 'SD' - spacedate.
  • The Chrono Quake in the Galaxy Angel games. After two centuries, the appearance of the White Moon over planet Transbaal established the new calendar, which is currently on its year 412 as of the first game, and 414 as of the third.
  • The Dragon Age series measures time against the establishment of the Andrastian Chantry and the crowning of the first Divine, with the current "age" (a period of one hundred years) used as an additional reference. Thus, something that occurred three years before that would have taken place in -3 Ancient (Age). Origins takes place in 9:30 Dragon (the 30th year of the Ninth Age, or "Dragon Age," 829 years after the crowning of the first Divine). The Tevinter Emperium measures time from its own establishment (TE), while the elves count the years from the founding of Arlathan (FA)—the ancient capital of the elves that has since been long wiped off the face of Thedas by the Tevinters.
  • The world of Darien from Total Annihilation: Kingdoms measures time in years since the magical apocalypse caused by the Kandran Precursors, after which point civilisation had to be rebuilt from the ground up and all magic was banned.
  • The EV Nova universe measures the New Calendar years against 2780 AD, the year FTL inventor Omata Kane died. At this point, a wave of offworld colonization began.
  • The Warcraft series uses the "ADP" calendar, or "After Dark Portal." The portal itself was opened just before the first game in the series, so the calendar is fairly new; it's only been about 30 years in-universe. We know from the first game's manual that the year 1 ADP was the year 593 in the humans' old calendar, though given there are a good 14,000 years of history in the series it's unclear what event a mere 600 years ago caused another calendar reset.
  • Analogue: A Hate Story has an unspecified drastic change in society on the spaceship, leading to a new year zero.
    • The sequel, Hate Plus, explains that the reset was due to an armed rebellion that, while ultimately failing, resulted in the computer records being wiped.
  • EverQuest II takes place in the year 500 A.K. After Kerafyrm. The awakening of an extremely powerful dragon named Kerafyrm in EverQuest set into motion a series of events that changed the face of Norrath forever, including deadly cataclysms that shifted the face of Norrath and broke up its continents; the Second Rallosian War, in which the nigh-unstoppable Ogre army steamrolled their way across most of Antonica, only to be felled by divine intervention; and finally the destruction of the moon, Luclin, and the Lunar Armageddon that followed. Even for the Ogres themselves, they used their own calendar system during the war, because they signaled it as the beginning of a new empire that would control all of Norrath.
  • Final Fantasy XIII-2 starts off in 3AF, or After (the) Fall (of Cocoon), three years after the end of the first game. Not only was everyone forced to start over entirely, leaving their past way of life behind, but time was literally warped as well, shaving the length of day down from twenty-six hours to twenty-four. Of course, it seems they also didn't really keep track before in the first place, with someone mentioning in the prequel novella that people from Cocoon don't even know exactly how long it's been since Cocoon was almost completely destroyed the first time.
  • Final Fantasy XIV has this in its backstory to such an extent that it's out-right expected to reset on a regular basis. The world of FFXIV regularly goes through cycles of "Astral" and "Umbral" Eras, which are used to date its calendar. Umbral Eras are triggered following a Calamity of some such that radically changes the world (known Calamities include the world being flooded from an overuse of the land's aether in a war between magic-users and the lesser moon Dalamud nearly being dropped on the planet), and are then followed by more peaceful and prosperous Astral Eras. Version 1.0 of the game starts off in the Sixth Astral Era until the Seventh Umbral Era is set by the Calamity of Bahamut's revival. 2.0 then picks up in the Seventh Umbral Era, and the Seventh Astral Era is declared upon completing the 2.0 Questline. While the Seventh Umbral Era only lasted about ~5 years, it's never said if there's any exact average; only the length of the Sixth Astral Era is known, and even then not exactly (just that it was almost 1600 years).
  • The world of Enroth in (the old universe, obviously) Might and Magic measured years in A.S — After the Silence. The Silence, in this case, is the year when Enroth lost contact with the Ancients. It is entirely possible that analogous calendars (just with different names for the Silence) was used on many other worlds, considering the Silence spanned an entire galactic arm.
  • Runescape had the calendar reset six times. The First Age (World Creation); Second Age (Era of the Gods); Third Age (The Cataclysmic God Wars); Fourth Age (Rebuilding civilization); Fifth Age (Age of Man); and the penultimate Sixth Age (Return of the Gods).
  • In the X-Universe series, a human starship lured a rogue terraformer fleet away from Earth and then blew up the Jump Gate behind them, but believed their gambit failed and that they were the only human survivors. They reset their calendar in 2170 AD to year zero and began to purge all mentions of Earth, then renamed themselves the Argon.
  • Gears of War uses BE and AE, for Before And After Emergence Day. It's not shown how they counted years before Emergence Day happened.
  • As revealed in a visit by Randy Varnell at the Battleborn Discord server, the Standard Codex Reckoning (C.R.) calendar of Battleborn came about because of a few very extra-ordinary things. One of those being the natural death of the star Celestis, leaving 1 million active stars to be tracked by the Eldrid on Codex. Other reasons that make year zero big are when the Varelsi first appear and begin darkening uninhabited systems; and Lenore discovering the science of Sustainment.
  • In the backstory of Anbennar, the elf mage Ducaniel crashed a flying city onto the Precursor Empire of the elves, said crash triggering a Fantastic Nuke wiping out all civilizaton and the majority of life on the continent of Aelantir. The rest of the planet was hit by earthquakes, floods, volcanic eruptions and a century long rain of ash in what became known as the Day of Ashen Skies, marking the year 0 of the calendar.
  • Project Wingman takes place in 432 AC, or "After Calamity," an event that involved many volcanic eruptions and earthquakes in the Pacific Ring of Fire, the eruption of the Yellowstone Supervolcano, large areas of land being submerged, and new islands forming.
  • The in-game library for Solatorobo: Red the Hunter mentions a regional variation of this trope: the Shepherd Republic's calendar starts from when the republic itself was founded (127 years prior to the game's events), following the Shepherd Revolution and the toppling of the prior Kingdom of Shepherd's royal family. Given that Shepherd is already a Fantasy Counterpart Culture to France, it's likely that this factoid is meant to reference the French Republican calendar that was created during the real-life French Revolution, prior it to being abolished when Napoleon later became emperor. That being said, the Japanese-only Daybreak art book clarifies that Shepherd's calendar uses the same measurements that we do, in contrast to how the French Republican calendar used decimal measurements instead.

  • In Drowtales, when the vast majority of the elven race was driven underground, the entered a new age of their calendar, 'The Moonless Age' since they no longer can see the moon(s). It has been 1100 years since and the kingdoms of drow now cover the underworld.
  • In Leaving the Cradle, the wiki describes the raharrs as having this when they discovered the stabilizers. The realization of their artificial nature threw the world into chaos and it led to mass hysteria, riots, and suicides. Their calendar got reset afterwards and they now refer to their history with P.R. and A.R. (Prior Realization and After Realization, respectively.) By the time the webcomic started, it's been 756 years since then.
  • Sarilho: Something drastic happened 508 years before the beginning of the comic events that compelled the Meditans to change their calendars. The Lusitanians don't seem to give it the same importance and continued to count the years as usual, so by the time the story starts they are in the year AD 2805.
  • The four "breakings" in The Dragon Doctors each started a new calendar. The current year is "625 4B".
  • The Order of the Stick is set in the year 1183 (now 1184). The calendar appears to date from the creation of the world. (Or its recreation, as the original world was destroyed.)
  • In Jack, the calendar got hit so hard it restarted back to the Biblical Genesis.
  • Homestuck: In the post-Scratch universe, as an alien takes over the world, her arrival is marked "0 Post Condescension", and years are counted from there.
  • Stand Still, Stay Silent takes place in Year 90-91, with year 0, Day 0 starting from the day Iceland closed its borders in response to the Rash pandemic (which consequently puts New Year's Day in autumn).
  • Sleepless Domain uses a calendar that denotes years as C.Y. We only know for certain it's at least 127 years after what event caused the calendar to reset, as a school lesson shown says that it was in that year a more democratic system was established. Months seem to be the same, though, as the comic takes place in September.
  • Played for Laughs in this Awkward Zombie strip, in regards to Orphaned Etymology. Since Chrono Trigger uses A.D. and B.C. despite not taking place on earth, the author jokingly speculates that 1 A.D. was when donuts were invented, and A.D. stands for 'After Donuts'.

    Web Original 
  • Orion's Arm uses the Lunar calendar based on the landing of Apollo 11 in Tranquility basin (years denoted AT, After Tranquility), after the Nanodisaster and the evacuation of Old Earth.
  • The two sequels to The Intercontinental Union of Disgusting Characters use years before and after the IUDC as their only system of datekeeping.
  • The world of Shadowside marks the start of Evo's Dawn in A.E. 2007 with "P.E.D. 0". (Post-Evo's Dawn)
  • Parodied in the post-apocalyptic Episode 10 of Knoxkast Radio, where Knox wonders if they should reset the calendar to Year 0. Jason instead decides to "do things differently this time" and declares that it is the year 8,036.
  • Dirigible Days starts in the year 997 from the Comet of Doom-induced collapse of civilisation.
  • AsteroidQuest numbers its years in "B.W." and "A.W." (Before/After Warp), since the invention of the Warp Drive ushered in a new Space Age.
  • Neopets uses years since the launch of the website for its in-universe calendar, with Year Zero being 1998 (the year the site was in development, but not live). It's unknown what calendar was used in-universe before then, but events that happened before that time are referred to as "BN" (Before [the discovery of] Neopia). For instance, if the Esophagor tells you that a given neopet that the Brain Tree wants to document died in 26 BN, they died in 1972.
  • The Tourettes Guy: Downplayed. Danny says a great big "PISS!" so loudly the calendar flips its page.

    Western Animation 
  • In Samurai Jack, the calender was reset when Aku conquered the world, as shown when a scientist scans Jack with a device that says he's from the year 25 B.A. (Before Aku).

    Real Life 
  • The ancient Roman calendar has a few:
    • The Romans did not usually use a continuous numbering system for their years, the way we do. Unique years were identified with reference to the political leadership of the state. Under the monarchy, this meant regnal years (the Xth year of King Y's reign). Under the Republic, they referred to the years as "[the year] X and Y being consul," which, naturally, was the year when the two individuals in question were consul. (During Julius Caesar's first consulate in 59 BCE, his co-consul Bibulus was so unpopular and so thoroughly stymied in his first attempt to seriously exercise consular power early in the yearnote  that he retreated to his house for the rest of his term; this left the field solely to Caesar, and people jokingly started to call 59 BCE "the year of Julius and Caesar being consul.") The consular-year naming continued after Augustus overthrew the Republic and established the Principate form of the Empire (in which the Republic nominally still ran like it used to and the Emperor was Just the First Citizen). However, after the Crisis of the Third Century, Diocletian's Dominate (basically the Empire saying, "why yes the Emperor is a king"), regnal years came back into use. When the Romans had to use a continuously-numbered calendar (e.g. in histories), they counted years from the foundation of the city of Rome — Ab Urbe Condita or A.V.C.
    • The Roman months are also worth a mention:
      • The original Roman calendar divided the year into ten months. The first month, Martius (Mars(=Ares)'s (Mars being the god of war and farming, activities beginning in the spring)), began on the vernal equinox, and after that came Aprilis (Opening, i.e. of buds), Maius (Maia (a fertility goddess)'s), Iunius (Juno(=Hera)'s),note  Quintilis (Fifth), Sextilis (Sixth), September (Seventh), October (Eighth), November (Ninth), and December (Tenth). The remaining two months' worth of time were not assigned to any month.
      • At some point, the Romans decided that this business of having unassigned time wasn't on for whatever reason. This time was thus divided into two new months at the end of the year, Ianuarius (Opening or Janus's) and Februarius (Purification, referring to a winter festival). This change is attributed to Numa Pompilius, the legendary second king of Rome.
      • Also with the months: In the 2nd century B.C., the beginning of the year was shifted from March to January in order to allow the newly-elected consuls to be ready for battle by the start of the campaigning season (spring). This change also seems to reflect a change in social practices at least a century earlier.
    • The last big change to Roman time was the Julian reform. The Roman calendar before Julius Caesar was a lunisolar one where each month roughly corresponded to one cycle of phases of the Moon. The advantage of the weird original Roman calendar with about 2 months' worth of time not actually part of any month was that it always aligned with the solar year; after December ended, the Romans of those days waited for the next vernal equinox to start the next year's Martius. The addition of Ianuarius and Februarius created a headache in that now that a year was supposed to be 12 months, it would start falling behind the actual seasons, and fairly quickly at that (12 lunar cycles comes to about 354 days, 11 days less than a solar yearnote ). As a result, the Romans added an extra "intercalary" month would be added to make the year line up with the seasons when the Pontifex Maximus (the chief priest of the Roman state) determined it was needed every 2-3 years.

      So far, so good—lots of ancient peoples ran their calendar like this. (For example, the Hebrew calendar at that time worked like this, but replace "Pontifex Maximus" with "Sanhedrin.")note  But in Republican Rome, there was a problem: Pontifex Maximus was an elected position, and candidates for the office were de facto almost always Senators. The Pontifex was thus almost invariably an active politician (Caesar himself held the post from 63 B.C. until his death). This in turn meant that he would invariably use his power to declare intercalary months to reward his friends with extra time in power or withhold months to punish his enemies with less.

      Also, political shenanigans aside, the Pontifex Maximus would (as a senior statesman) usually spend significant time as a governor of an outlying province or otherwise have business outside Rome, which meant that he was frequently not actually in the city when the intercalary month needed to be declared. Since the whole system depended on the Pontifex Maximus being in Rome to keep the calendar running, this usually meant that if the Pontifex was outside Rome at the relevant time, the intercalary month would just not be declared. As the intercalary month was usually declared in the middle of February (don't ask how), and thus during the middle of preparing for campaign season in the spring, good luck getting a Pontifex Maximus who was governor of a province trying to suppress a revolt or conquer a new province for Rome to come back to declare a new month (like, well, Caesar, who spent most of his Februaries for his ten years as a governor preparing his legions to fight in Gaul).note 

      This got the calendar completely out of line with the seasons, and so Caesar (once he held such absolute power that he no longer needed to abuse his powers as Pontifex Maximus — and was actually in Rome when the new month needed to be declared) started looking for a way to fix the calendar.

      Caesar found what he was looking for in Egypt. While chasing Pompey around the Eastern Mediterranean, he encountered the Ancient Egyptian calendar, which ignored the Moon completely and simply made every month 30 days long, with an additional 5 days belonging to no month as a kind of festival time at the end of the year. Caesar liked this system, although he had two problems with it: it still meant the dates would get out of line with the seasons, albeit at a much slower rate,note ) and the concept of days with no month annoyed him for some reason. To address the first problem, he added a sixth additional day to the year every fourth year.note  To address the second problem, the six days were distributed among the months of the year. To commemorate these changes, Caesar then renamed Quintilis, the month in which he had been born, Iulius after himself. Augustus would then rename the following month Augustus after himself to commemorate the Battle of Actium.
  • A 6th century monk called Dionysius Exiguus ("Little Dennis") is believed to have been the first to have dated the calendar from the birth of Jesus of Nazareth; his calendar was popularized by its use in Bede's writings, leading to the B.C.note /A.D.note  system most commonly used today. Dionysius's calculations, however, were criticized as inaccurate as early as the 12th centurynote , and were not universally adopted even in Christendom.
    • In the 19th century, the use of B.C.E./C.E. (for "[Before] Common Era") was proposed instead, as a religion-neutral name for the same system. Adoption of the terminology has been mixed, but there's no denying that the system is the "common" one. ("We don't accept your religious beliefs, but damn does having one calendar for everyone make things so much simpler, and damn do you Europeans have one of the best calendars around."note )
    • The shift from the Julian to the Gregorian calendars took place among Roman Catholics in the 16th century, but was not commonly adopted among non-Catholics until about the 18th note , leading to a difference of some eleven days. This is why some dates like George Washington's birthday will appear as February 11 (O.S.)note  and February 22 (N.S.)note , and why Miguel de Cervantes and William Shakespeare died on the same date (April 23, 1616), eleven days apart. Russia held out into the early 20th century, not adopting the Gregorian calendar until after the communist revolution. Hence, the October Revolution actually took place in November. The Russian Orthodox Church still uses the Julian calendar, which is why Russians celebrate Christmas on January 7th.
  • Very few written records survive about The Viking Age, and no primary sources written from the Viking perspective but the impact they made on culture left many traces in culture, traces that remained even when Norse Mythology was forgotten from cultural memory and all the Vikings had converted to Christianity and abandoned their polytheistic beliefs. What are these traces, well in Continental Europe, the days of the week are named after Roman and Greek deities and the names used in the Latin and Roman era. In the Anglophone however, local gods were used:
  • Many empires and kingdoms have changed calendars every time there was a new ruler, a concept referred to as regnal years.
    • Although The United States doesn't use this in everyday business, formal Presidential proclamations and other official federal documents (e.g. legislative bills and stuff like a certificate an attorney gets when they are licensed to practice in a federal court) will give years in both the Gregorian calendar year and the year of America's independence (which is, rather obviously, equal to the Gregorian year - 1776).
    • This, as well as numerous gaps in written records, is why China's history is so maddeningly vague sometimes.
    • Japan, still having an emperor, does it as well. 2019 was Year 1 of the Reiwa Era. They use these alongside Common Era numbering, and it's common to hear people speak about dates in the Common Era only, as it's more manageable mentally.
    • References to regnal years in the West are typically only seen in limited contexts with direct links to the monarchy; the most common one is probably references to regnal years in the Acts of the UK Parliament until 1963 (when they were replaced with Gregorian years) and Canadian Parliament to this day.
    • The use of A.D. is, from a Christian point of view, a prime example of regnal-year numbering: Christ is the King of Kings, and since His first arrival on Earth, he has reigned for [current Gregorian year] years.
    • Regnal dating, combined with the loss of historical records for entire periods of reign makes the Egyptian dynastic timeline a matter of extremely hot debate in Egyptology circles. While some gaps are simply due to the loss of records over time, others are due to various pharaohs purging the official records of any mention of their rivals or predecessors, and deliberately destroying or defacing monuments. It also doesn't help that the Egyptians had a strong aversion to—bordering on a taboo against—stating the date or circumstances of royal deaths in the annals and the royal funerary texts and inscriptions.note  Thus what would be a pretty normal, even standard, entry in the annals of most other historical monarchies—something along the lines of "His Majesty died on the sixth day of the fourth month of the twenty-fifth year of his reign of a surfeit of palfreys"—would be a marvelous find (suspiciously marvelous, in fact) for an Egyptologist.
  • Chinese emperors had a tendency to declare a new era every few years for any number of reasons, often to commemorate some sort of auspicious event or achievement. This practice was introduced in the Han Dynasty and lasting up to the Ming Dynasty when it was replaced by a system with one era per emperor. This was also adopted by the Japanese, where it lasted until the Meiji Restoration.
  • During The French Revolution, the Revolutionaries decided that 1792, the year the first Republic was founded marked a new Year Zero and to this end they made a new calendar. 1792-93 marked Year I and France counted years that way until 1805. In day to day life, the Gregorian calendar still remained in use and the Revolutionaries used the old days of the week as well, but the dates and months were used in official documents and signs, some of which still exist in France:
    • Each month had thirty days organized in three weeks called Decades, the tenth day of each week was called the decadi and a public holiday. Five extra days were added to the end of the year to make a total of 365 days a year; these 5 monthless days were dedicated to public festivities. A leap year likewise had six extra days, with the sixth extra day being extra-festive.
      • Each year had 12 months divided into sets of three months to reflect the four seasons of Autumn (Vendémiaire note , Brumaire note , Frimaire note ), Winter (Nivôse note , Pluviôse note , Ventôse note ), Spring, (Germinal note , Floréal note , Prairial note ) and Summer (Messidornote , Thermidornote , Fructidornote ). The real problems with the use of the calendar aside from widespread cultural inertia with the Gregorian calendar, is that the new months while corresponding well, more or less, with the seasonal structure of France was not quite as appropriate to the colonies where a Snowy Month (Nivôse) doesn't snow and so on.note  The other issue was that there were only three weekends or decadis, rather than the four-to-five Sundays per month in the Gregorian leading workers to complain about having their free time taken from them.
      • Interestingly, this is almost exactly how the Ancient Egyptian solar calendar worked—12 months of 30 days, each month consisting of three 10-day weeks, the 10th day of the week being a day of rest, with five festival days at the end of the year. The only significant differences were that (1) the Egyptians also took the ninth day of the week as a day of rest (at least for artisans during the New Kingdom) and (2) the Egyptians didn't have leap years (for reasons still not fully understood) until Augustus forced the issue (by ordering the Egyptian priesthood to modify their calendar to keep it permanently in sync with the Julian calendar he'd inherited from his late uncle). Even more fascinatingly, the architects of the French Republican calendar were at best only vaguely aware of the Egyptian calendar; while records of its later forms were available, they were obscure, and they may not have said anything about the 10-day weeks. Great minds think alike, one supposes.
      • The reason the Republican months still remain well known is that it was introduced in the famous year of 1793-1794, the year of the Terror, and several months and dates, have become proverbial in terms of its gravity of impact. The most well known dates on the calendar is 9 Thermidor year II, the Fall of Maximilien Robespierre, and 18 Brumaire year VIII, the coup that brought Napoléon Bonaparte to power.
    • The same people who came up with the Republican Calendar also tried decimal time within the day, dividing one day into 10 hours, each hour into 100 minutes, and each minute into 100 seconds. However, this never really caught on even within the Republican government, largely because all the clocks were already using traditional 24-hour time and it would be stupidly expensive to replace every clock and watch in France with a new decimal one.
  • North Korea has the Juche calendar, with Juche 1 being 1912, the year of Kim Il Sung's birth. It did not replace (yet) the common world calendar but most North Korean publications include both dates. For instance, something published in 2013 will be dated "2013 / Juche 102".
    • Taiwan has a similar system, which is based on 1911 (the establishment of the Republic of China) being Year 0. 2013 would be "the 102nd year of the republic".
    • In Virginia, very formal state documents are likewise marked according to the common reckoning, and a "Year of the Commonwealth", with 1776 as Year Zero.
    • Many formal documents like Law Degrees in the United States are stylized in the Year of Our Lord X, and of the Independence of the United States the n'th. The U.S. constitution is dated, "the Seventeenth Day of September in the Year of our Lord one thousand seven hundred and Eighty seven and of the Independence of the United States of America the Twelfth".
  • When Pol Pot took control of Cambodia, he abolished the old calendar and declared the first year of his dictatorship to be Year Zero.
  • In Fascist Italy, Roman numerals were used to denote the number of years since the establishment of the government in 1922 alongside the more common calendar.
  • Very close to the definition of this trope is the Islamic calendar ("Hijri"), which started when Muhammad and his followers emigrated from Mecca to Madina. The enemies of the Meccan Muslims were about to assassinate Muhammad.
  • Midnight GMT on January 1, 1970, was chosen as "Second 0" to define the UNIX epoch. It was picked arbitrarily and not expected to be around for long, especially since we are going to run out of digits on January 19, 2038 (at 03:14:07 UTC), using the original method of storing that time (count one per second since the epoch: simple as can be; it's just they didn't anticipate UNIX surviving for over 2.1 billion seconds — the amount of seconds needed to go through 31 bits). Some newer systems have tried to fix this by doubling the size of the field used to store this information, so that the calendar will still work for eons and eons.
  • The Church of Scientology dates its calendar from 1950 and the publication of "Dianetics".
  • The Coptic Orthodox Church of Alexandria marks its time from 284 CE, the first year of the Emperor Diocletian. Why? Diocletian initiated the last Roman persecution of Christians, and since Egypt was pretty much majority-Christian by then, they felt the persecution particularly hard there—and so the era for the Coptic calendar is "Year of the Martyrs".
  • On the Maya:
    • All that fuss about the "End of the Mayan Calendar" in 2012? That was literally just this, not anything apocalyptic. They had (and still have) one calendar for day-to-day use, but it reset every 52 years, so they had another one, the "Long Count", for recording historical dates. 2012 was just the end of the 12th b'ak'tun (394-year cycle) — which isn't even a particularly significant number, as they go up to 20note . Much more interesting a date is October 13th, 4772, the end of the first piktun, 7885 years after Mayan Year Zero. Even that isn't the longest calendar they had — an alautun is over 63 million years long.
    • From a social point of view, social unrest and disasters were outright predicted to happen every 52 year reset, mythologised in the myth of Chak Ek. So essentially the calendar is calamity proof, and attests to the cycle of rise and fall of cities in Mesoamerica.
  • In general, this is the case. It took a long time for people to discover that a "year" took approximately 365 days. Eventually it was discovered to be closer to 365.25. This means that every 4th year of the calendar will contain a leap day added to February to make up the difference and thus the year will be called a leap year. In modern times, it was narrowed down to 365.2425. This means that every 100th year, that year will not be a leap year and not contain a leap day, except every 400th year WILL be a leap year. This works almost perfectly except for the fact that the length of a year has slowly been changing for all of Earth's history (as does the length of a day thanks to the moon slowing down the Earth's rotation). For the purposes of the modern Gregorian calendar, with the invention of atomic clocks and exact measuring systems, we can make changes to the calendar without causing the aforementioned Shakesperean paradox where two people can die on the "same day" despite having died actual days apart from each other. This also makes it simpler for lay people as they don't need complex math to figure out the year while the scientists who use complex math anyways can figure it out for us. Even as science, religion, and politics became more and more separated, the Gregorian calendar has stayed more or less intact because it would be too confusing and controversial to switch over to something new (which is also one of the reasons why other cultures refuse to give up their own calendars and also to thumb their noses at the church as Isaac Asimov claimed).
  • While in general a year zero based on the first nuclear detonation never caught on, geological dating does use a nuclear weapons based calendar. Rock formations and the fossils found in them are dated to years "Before Present", with "Present" being defined as 1950. The last year before above-ground nuclear tests significantly altered the ratio of carbon isotopes in the atmosphere.