Follow TV Tropes


Writers Cannot Do Math / Anime & Manga

Go To

  • Dragon Ball:
    • The eponymous objects can't be used for one year after they grant a wish, but only 8 months pass in between the first use in the series and the second one.
    • If your family name is "Son", your age is going to get very confusing: Goku first claims to be 14, but nearly a year later claims that's because he thought 14 came after 11 so he's actually 12, yet according to the first point above, a year passed since he first gave his age, so he should be 13 (Then again... maybe his birthday is somewhere between May 7th and September 1st. It's not like Goku knows his birthdate anyway. Or he was wrong the first time too). Gohan's age at the start of the series is four. In the Buu saga, thirteen years later, his age is given as 16 when he should be chronologically 17, physically 18.
      Goten is 7 when we first see him, but just under 7 years went in-between the Cell saga and its Time Skip to the Buu saga, so in order for him to be 7, he should have been born (not just conceived) during the Androids saga... where Chichi didn't even look pregnant. Figures.
      • Dragon Ball Minus (and by extension Dragon Ball Super: Broly) fix the issue with Goku via Retcon: Whereas the original Dragon Ball had him arriving on Earth as a baby, the new version shows him him as a toddler, which would mean his original assessment 14 was accurate after all.
    • Advertisement:
    • It is clear that Akira Toriyama has NO idea what a kilogram is. In Goku's second match against Tien he reveals that he has been fighting wearing 100kg of weighted clothing. Sure, that would be excessive in real life, but this shocks the guys who casually jump hundreds of feet into the air and shatter rock with their bare hands. Later on, the concept gets even more ridiculous; Goku, who in the beginning of the series is seen casually carrying a giant tree that must weigh a thousand tonnes, struggles to lift ten times his own body weight when he reaches King Kai's planet.
    • In Battle of Gods, Bulma has her 38th birthday, even though she was 16 at the start of Dragon Ball and the movie it set 29 years later. While you could potentially construe this as her lying about her age out of vanity, Mai of the Pilaf gang, who was turned into a child along with Pilaf and Shu and trying to blend in with the party, accidentally says her real age is 41—despite clearly being older than twelve when she's first introduced.
  • Naruto has numerous inconsistencies with character ages compared to state time periods, mostly because these ages are only in the databooks, so the author either doesn't remember them or doesn't care about later contradicting them:
    • A comment by Zetsu in Part II stated that Orochimaru left Akatsuki after trying to take Itachi's body 10 years ago, meaning Itachi was in Akatsuki two years before the Uchiha Massacre, and was 11 at the time.
    • Supposedly Orochimaru conducted the Mokuton experiments on infants, or at least young children, but Yamato's age is given as 26 in the second part of the manga, and Orochimaru didn't know that he had survived because the experiments' discovery was what forced him to flee the village. This would mean that he left Konoha at least twenty years before the start of the manga. However, Anko is currently 24, but was somehow Orochimaru's student that far back (the databooks even say she was 10 when she graduated the academy). Likewise, Jugo is 18, but since he's what Orochimaru based the Cursed Seal he gave to Anko on before defecting Orochimaru would have also have to have met him before defecting. So either Yamato should be younger or Anko and Jugo should be older.
    • Advertisement:
    • When Killer Bee is fighting Kisame there are some counting errors in the art: When he starts going into his tailed beasts forms, one form is shown with eight tails, but someone on the sidelines says there are seven and when he's reduced to one he says he lost six of them. When he takes another form we see seven tails in one panel, but eight in the next two. These were both corrected in the volume version: the first form had one of the tails erased and the second had a tail added.
    • Konoha's ninja population seems iffy. During the 4th Shinobi World War, we are told that the Allied Forces comprise some 80,000 ninja and samurai. Konoha supposedly has the largest population of any ninja village, but even if each village and the samurai contribute the same amount of soldiers, Konoha would still have to have at least 13,000 nin. Though we only ever see the same 50 Konoha ninja, this is still possible. It's just that, according to Kabuto, there were 87 Konoha genin in the Chunin exam and, even accounting for genin who couldn't or didn't want to particpate, that seems like an incredibly small ratio. At the time of the chunin exams, the Rookie 9 are apparently the only new genin in Konoha (Kakashi even outright stated this during the Team 7 bell test). The academy exams are done twice a year, so that would mean that Konoha graduates at most 18 ninja a year. To put this in perspective, it would take 723 years to get 13,000 ninja this way. And that's not taking into the account the fact that Konoha was involved in three other world wars and countless other conflicts (including the Uchiha Clan Massacre) that no doubt had taken out a large chunk of its ninja population...
    • Even disregarding the above, Konoha, with its several hundreds-odd non-high rise buildings until the Boruto series (since it's still technically, y'know, a village), doesn't seem to be the type of community that could support tens of thousands of commoners, let alone ninja, though this can be easily handwaved by thinking that Konoha ninja don't necessarily all come from the village and instead hailed from elsewhere in the Land of Fire.
    • Kakashi supposedly graduated from the Academy at age 5, and he became a chuunin by age 6. Obito and Rin both graduated at age 9 and became chuunins at 11. This means that for the three of them to be on same team during the time of Kakashi Gaiden, either both Obito and Rin should've been four years older than Kakashi, or Kakashi wasn't part of the same rookie gennin team as the other two, and joined them as a chuunin. However in a flashback to their first chuunin exam, they all look the same age, which is further supported by that Rin already had a crush on Kakashi, which would've been rather weird if he was six and she was ten, and they are on the same gennin team.
    • The same chapter basically retconned the ages and graduation ages of every known adult to be in the same class. So apparently nobody graduated from Konoha for the next decade, or it's an incredibly coincidence that all known adults graduated around the same time.
    • The students in Obito's class in Kakashi Gaiden are previously established characters, but of wildly different ages. Raido and Hayate, both shown in the class, were previously established as being 9 years apart.
    • Iruka allegedly became the class clown after his parents died due to how lonely he was. Problem is, Iruka was 14 when they died and had graduated when he was 10, thus when his parents died he'd already been a genin for four years.
    • Supposedly a single Ryo is worth roughly ten cents, however a single D-rank mission (which consists of chores like weeding, grocery shopping, and babysitting) costs a few thousand Ryo. So not only are people spending hundreds of dollars to have their fence painted, but there should be far less drive to reach higher ranks if a Genin can easily make a living wage just doing one or two D-ranks a day and never risk death on a mission.
    • It's mentioned that Naruto has failed the academy graduation test several times. This doesn't make sense because it's been shown that he began at the same age as everyone else. Naruto is actually several months younger than the rest of the Konoha 12.
  • In an episode of Digimon Savers, Marcus Damon has a flashback of one of his birthdays, in which he fell and tore open his head and his father ran him to the hospital. In the original Japanese, which birthday this was isn't stated, but in the dub, he had just turned six. How can this be possible if Marcus is 14, and his father has been missing for 10 years?
  • In an episode of Doraemon, Doraemon gives Nobita a special plate of cookies that double every 5 minutes (so if he starts with one, after 15 minutes he will have 8 cookies), warning him that he must eat every single one of them quickly. In the end, he throws away one and returns after a while to find a big pile of cookies. Unable to eat them all, they choose to throw them to space, and later Doraemon tells Nobita that a whole galaxy made of cookies has formed. In reality, if they doubled every five minutes, in less than 15 hours the mass of the cookies would be many orders of magnitude larger than that of the whole universe. Oops.
  • In the original version of Yu-Gi-Oh!, in Yugi's duel with Weevil Underwood at the start of the Duelist Kingdom arc, Yugi plays a card that raises Summoned Skull's attack power by 30%. 30% of 2500 is 750, but the attack counter goes up by 1000 points. This was corrected in the dub version.
  • In Yu-Gi-Oh! GX, in the first duel against the Supreme King, there is one sequence where the King takes damage. Except that the damage he actually took is about 100 less than the damage he should have taken. This is egregious because had he taken that extra 100 damage, he would have wound up losing the duel. The same scoring error appears in Yugi's duel against mind-controlled Bandit Keith. Then again, since Keith is quite explicitly cheating, Yugi deserves a few extra lifepoints to give him a fighting chance.
  • Steins;Gate, of all things, has a pretty serious error when it comes to Ruka's message. It is sent back in time seventeen years to Ruka's pregnant mother, in the hope of changing her child's sex from male to female. However, it's been established that one second on the Phone Microwave (name subject to change)'s timer corresponds to one hour back in time, and seventeen years is about is 150,000 hours. The microwave's counter only has five digits, and presumably can't go over 99,999. Given the level of detail and accuracy in the rest of the series, it's entirely possible the staff noticed the former error and instead of trying to correct it, simply went "Fuck it" and left it that way.
  • In Mitsudomoe the class is playing anything goes chairs at the start of the manga and anime. The rules are simple — there are enough chairs in a circle to seat all but one member of the class. Whoever is left out has to call out a criterion, anyone who matches that criterion has to leave their chair and find a new one. After their initial rush for seats it appears that everyone in the class is seated. The teacher is confused at first thinking that there should be exactly one seat less than there are people — it turns out the eldest daughter Mitsuba is sitting on a classmate who is on all fours. Catch is, if she is sitting on a classmate instead of chair then there are two people not in chairs and thus an empty chair somewhere which would have been obvious.
  • In a Black Butler OVA, Thomas Wallis was born in 1775, and his scheduled death date was 1779. This would be fine if the boy didn't appear to be in his early 20s at the time of death.
  • In a season two episode of MegaMan NT Warrior, Numberman is tied to a giant bowling pin by Bowlman, who starts knocking pins down. Numberman calculates the odds of his pin being hit as 10%, 20%, 30%, etc as the pins fall. Even if one assumes that Bowlman will only hit one pin with each ball, and that the odds of any given pin being his is identical (Which is most definitely not a sensible assumption when bowling), the odds of Numberman being hit would have been 1 in 10, followed by 1 in 9, 1 in 8, etc, or 10%, 11.1%, 12.5%, 14.3%, etc.
  • The seven and a half year time skip in Fairy Tail manages to add exactly seven years... to the time when the story began. If you keep track of the dates it's actually been half a year since the story started, meaning an entire year just went missing somewhere.
  • Rave Master:
    • Haru claims to have been fighting for the sake of the world for two years, when every bit of evidence to come before and after that says he's been at it for one.
    • Hiro Mashima freely confessed to miscounting the number of chapters he had left before he had to end the series. This meant that while several fights in the final arc involving the Quirky Miniboss Squad and more peripheral members of Haru's gang lasted a good long while, Haru's own fight with Lucia ended a chapter early, and another intended chapter where the two talked afterward was shortened to a single page.
  • Bakuman。, or rather, PCP. "The only month this year in which the 9th is a Thursday is July." That's impossible: July 9th and April 9th are always the same day of the week.
  • In chapter 156 of Assassination Classroom, it is stated that there are 26 days remaining until a March 13 deadline. That would make the date February 16 in a leap year, February 15 in a regular year. Two chapters later, it's Valentines Day.
  • Early in Fullmetal Alchemist Brotherhood Isaac Mcdougal says at one point that water is over 70% of his body. There is an in-universe formula for human bodyingredients  and according to this formula water is about 60% of human body.
  • In the H-manga Dulce Report II, a principle character is said to age at a rate of five times faster than a normal person due to LEGO Genetics. However, she appears to be a Second Year Protagonist and her conception happened five years ago not three. As there is no mention of her gestation taking longer or shorter the math doesn't agree with what is stated having her age at rate of around 3 times, give or take a few weeks, faster.
  • Clockwork Planet loves to throw a lot of numbers around, especially when it comes to gears, but there are a few mathematical discrepancies found that don't match the actual equations well or are just plain wrong.
    • This paragraph quoted from page 126 of the first novel.
      "Right now, Marie and her staff were working 8,200 meters below the city grid - the third floor of the core tower. Even this elevator, which moved at a speed of 1,000 meters per second, took eight minutes to travel one-way between the surface and the third floor."
    • If the elevator was exactly moving 1,000 meters (1 km) per second at a distance of 8,200 meters (about 8 km), it would actually take the elevator eight seconds to reach the third floor from the surface, not eight minutes, clearly not enough time for Marie to forcefully interrogate the Technical Force officer for information. For the elevator to reach the third floor in eight minutes, it would have to be moving at a much slower speed than what is described in the novel. Estimates would put the actual speed of the elevator at around 17 meters per second.
    • Another discrepancy found in the first novel is that Kyoto's core tower is mentioned to be 50,000 meters (50 km) in diameter. This is in reference to its width, since the tower's height is listed at 90,000 meters (90 km). However, if the core tower was actually 50,000 meters across, it would be much larger than even Kyoto itself, which contradicts the official illustrations in the light novels and manga showing core towers to be no wider than a couple of buildings in one block. The average width of a Japanese high-rise building is about 30 to 50 meters, so measuring the distance of an entire block of buildings would put the actual diameter of the core tower at around 150 meters.

How well does it match the trope?

Example of:


Media sources: