Mark: Oh... I don't got no birthday. At least I don't know when it is.
Jennings: How old are you?
Mark: I don't know. Maybe eight or nine. Something like that.
Maybe they grew up an orphan, maybe they have amnesia, or maybe they just grew up in a society that doesn't celebrate the day someone is born. Either way, this character doesn't have a birthday. This usually comes as a shock to their peers.
Oftentimes, the character will be assigned a birthday based on an important date in their life. It may not be their real birthday but the idea is still the same. Sometimes, their friends, being shocked that they have Never Had a Birthday Party, will also throw them a party.
May lead to Vague Age. If the character doesn't remember their birthday, this often relates to a Mysterious Past. One of the reasons a character may have Never Had a Birthday Party. Often caused by the same reasons a character was Never Given a Name. Compare Forgotten Birthday for when a character's friends/family forget their birthday and Forgot Their Own Birthday for when a character forgets their own birthday. This may also go along with a Birthday Hater.
- Chainsaw Man: Denji says he "thinks" he's sixteen years old, suggesting he doesn't know his exact birthday. It's implied basically getting abducted into slavery by mobsters at a young age has made his existence largely undocumented. Regardless, he later holds a party for his seventeen birthday; if they found his birth on record or just guessed an arbitrary date is unspecified.
- In Rebuild World, Akira doesn't know where or when he was born outside of being in the slums, nor had anyone told him the date until he was older. Because of this, he doesn't know his own age or birthday. This is apparently common among slum kids like him.
- Re:Zero: Felt, an orphan girl living in the slums, doesn't know her birthday and guesses that she's 15.
- Honey Badger doesn't know her date of birth, being a clone. The Stepford Cuckoos have a similar predicament, but decided to arbitrarily pick a day based on the birth date of their favorite actor.
- In Supergirl: Being Super, Kara doesn't know her birthday or her exact age. She was a refugee from another planet who suffered amnesia. It's assumed she's around sixteen.
- In All-Star Superman, our hero doesn't know when his biological parents' birthdays are, so he's arbitrarily marked two dates six months apart as the days that he'll celebrate them. Since he's the only one observing themnote , it doesn't really matter.
- The Unstoppable Wasp: Nadia was raised in the Red Room, and doesn't know when her birthday is. The Champions and Young Avengers end up throwing a birthday party for her when they hear she's never had one.
- The chapter "Birthday" of the Avantasia Protag AU series revolves around the main characters all realizing none of them know their birthdays. For Gabriel, it's because birthdays weren't celebrated in his time. For Scarecrow due to severe child abuse. Aaron was orphaned at a young age and just never thought about it that hard. And Entity doesn't remember anything about his past anyway. They decide to celebrate as a family all on the same day, but instead of it being an important date for them, it's just a random date on the calendar. (However, it IS a Significant Reference Date and Easter Egg for those who recognize it as the real life birthday of their canon creator.)
- A RWBY fanfic (written before Volume 4) revolved around Blake being a Birthday Hater because she didn't know her own birthday.
- As Emerald was an orphan before Jaune adopted her in Relic Of The Future, they celebrate the day he met her as her birthday instead.
- Likewise in A Monster's Marriage, Jaune decided on May 10th for Emerald's birthday since she didn't have one before they metnote .
- Applies to Celestia and Luna in the Triptych Continuum. Justified because keeping exact time in the Discordian Era was impossible: they know they're about two years apart, but they don't have recorded birthdates because there was nothing to record them against. (Any given location was lucky to have seasons.) There are dates on which their birthdays are celebrated, but those come from the consensus of the herd.
- In the American Girl book Happy Birthday, Addy!, Addy tells a neighbor she befriends that she and her parents don't know her birthday because she was born in slavery and slaves didn't have access to calendars; they only know that she was born in the spring. The neighbor then suggests (and Addy's parents agree) that she can pick a day around the right time of year and call it her birthday. She ends up picking April 9th, the day that the North officially wins the Civil War.
- Briar Moss of the Circleverse grew up as an orphaned street rat and has no idea exactly when he was born. He's told to just pick whatever date he likes, and he eventually chooses the day he first met Rosethorn.
- Isaac Asimov and Robert Silverberg's The Positronic Man: In chapter three, Andrew witnesses a birthday party. He starts to wonder when his birthday would be and what he would use to determine it. Nevertheless, the hundred-and-fiftieth and two-hundredth anniversaries of his construction are publicly celebrated.
- In Loskutik And The Cloud, Loskutik, a poor orphan who has lived her entire life as a servant to abusive masters, doesn't know when her birthday is.
- In the Modesty Blaise series, Modesty was orphaned very young and doesn't know her real birthday (or anything else about her birth family; even her name is one she acquired later). In The Impossible Virgin, when Sir Giles says that at his age he doesn't bother celebrating birthdays, she says that she uses it as an excuse to celebrate her birthday three times a year.
- In The Pinballs, Thomas J. doesn't know his birthday, since he was a Doorstop Baby and the authorities are still trying to figure out his real identity. His foster sister Carlie tells him that he can share her birthday for the time being.
- In the autobiographical book They Cage The Animals At Night, Jennings' friend Mark has lived in orphanages his entire life. He doesn't know his birthday or even his exact age.
- In the Treehouse book "The 52-Storey Treehouse", Andy and Terry don't know their birthdays or how old they are, so they decided to add a room to their treehouse where it's "everyone's birthday even if it's not" and create an official "proxy-birthday" for both of them to share.
- In the first Red Dwarf book, while applying to the Space Corps, Lister gives his date of birth as "unknown", due to his being found in a cardboard box under a pool table.note When asked when he celebrates his birthday, he replies "most of the time". Eventually the interviewer puts 14th October, based on the fact that he was found in November and believed to be about six weeks old, but it's pretty much just a guess.
- In Wolf Hall, Cromwell doesn't know his birthday (as people who weren't born into the elite/nobility at the time rarely paid attention to birthdays), which doesn't stop astrologers from trying to figure it out based on his personality and current position.
- Space Cases: In "It's My Birthday, Too (Yeah!)", it's revealed that Radu doesn't know his birthday because those of his kind are born in hatcheries, and he lies that it's his birthday so he can have his first party.
- Jack in Power Rangers S.P.D. says that he doesn't understand why Syd is upset when he makes her work on her birthday. It's eventually revealed the reason for this is because he doesn't know his own birthday. By the end of the episode, she decides to share her birthday with him.
- Agents of S.H.I.E.L.D.: Daisy Johnson/Skye spent her whole childhood frequently changing among foster families without ever knowing her biological parents, therefore she never knew her exact birthday. When she manages to reunite with them, she learns that she was born on July 2, 1988, not in 1989 as she'd previously believed.
- In the Grand Finale of M*A*S*H, B.J. couldn't make it home in time for his daughter Erin's birthday, so the camp cheers him up with a birthday celebration for a Korean orphan whom they claim was born on the same day as Erin. They later admit that they have no idea when the Korean orphan was born, and they just selected a child who looked to be the right age. B.J. is still touched:
B.J.: What better birthday present to get than your own birthday?
- I Dream of Jeannie: In the two-part story "The Girl Who Never Had a Birthday", Jeannie tells Tony that she does not know her birthday. However, she does know that Neptune was in Scorpio on the day that she was born. Tony and Roger try to find out the date of Jeannie's birthday by feeding this information into the NASA computer ERIC. After several failed attempts to access the computer, Roger finds out the date but Dr. Bellows ships him off to Alaska before he has a chance to tell either Tony or Jeannie. He eventually returns two episodes later in "My Master, the Great Caruso" and tells Jeannie that she was born on April 1, 64 B.C.
- A variant in Everybody Loves Raymond: Frank and Marie lied to Robert about his real birthday to keep people from finding out that he had been conceived out of wedlock. He only learns the truth decades later — on his actual birthday.
- The Musketeers: Porthos' mother died when he was very young and he grew up alone on the streets. As a result he doesn't know when he was actually born and his "birthday" is just a random date he picked off the calendar so his friends would have a day to celebrate.
- A variation occurs in Finding Carter. The eponymous protagonist, a teenager who recently learned that her "mother" actually kidnapped her when she was a toddler, thought she knew her birthday, but after she's returned to her birth family, she learns that her real birthday is nowhere near the date on which she'd been celebrating her birthday for most of her life. Her twin sister later tells her that the date she had been told was her birthday was actually the anniversary of her kidnapping.
- On 30 Rock, Tracy doesn't know his birthday, and never had birthday parties as a child. Kenneth then gets Jenna to agree to share her birthday this year.
Tracy: I don't need a birthday 'cause I buy myself all the presents I need. And because of my drinking, they're often a surprise.
- BlazBlue has a variant. Noel was told by her foster-parents that her birthday was December 25, and that's where her name comes from. She was actually smelted on January 7th. The other birthday was implanted, along with all memories of her childhood, to disguise her age even from herself. The games imply her friends continue to celebrate her birthday on Christmas because that's Noel's birthday and Clones Are People, Too.
- Fire Emblem: Three Houses a disguised example. While Byleth's date of birth is chosen by the player, they do have a canon birthdate as well. As in, one that's always canon, revealed as part of the plot. It's hinted the player-chosen birthdate actually belongs to Sothis, which Byleth osmosed thanks to Sharing a Body. As for why he's never corrected on this despite growing up with an active and loving biological father, it's hinted Jeralt deliberately left Byleth in the dark about their own youth just in case he ever had to lie to Rhea about it.
- THE iDOLM@STER: SideM has Kei, a man so listless he doesn't know when his birthday is, let alone his age. The Producer and others know enough to help him celebrate every year, so they remind him when the time comes.
- Wilhelm Ehrenburg from Dies Irae was born into destitute poverty during WW1 and post war Germany, and as such, there are no documents of his birth and his family was a pretty dysfunctional one as well so they didn't really keep track, something he notes wasn't uncommon during that time. He believes he was born sometime in 1917 but admits that its about the best guess he can manage.
- A Little Lily Princess: Becky doesn't know on which day of the year she was born, as she grew up in a workhouse. The authorities there decided she was old enough to be sent to the Boarding School in which the sotry is set to work as a scullery maid as an educated guess more than anything else. Sara suggests that she share her birthday, an idea that she likes very much.
- Gawr Gura from hololive has been around long before the modern Gregorian calendar was invented, indeed longer than before humans began recording the passage of time. She also doesn't remember exactly how old she is anymore, but knows it's somewhere after 9000 years. For this reason, she declared June 20th as a Significant Birth Date because it's the day when Jaws was released in theaters.
- Strong Bad Email: In "cheatday", when asked about celebrating The Cheat's birthday, Strong Bad admits that no one actually knows when The Cheat was born. So they just celebrate his birthday on the one day they're sure it isn't—the date listed on The Cheat's (obviously fake) ID card.
- Slightly Damned: Buwaro dosen't know when his birthday is, on account of him being orphaned before he hatched and Darius having stopped recording the date by the time he found him.
- In Goblins, Minmax tries to find something "normal" about Kin, but gets irritated as she comes from such a wildly different culture; she doesn't even know her own birthday. Minmax debates what to do about this, ultimately deciding to give her one "normal" thing: a birthday party.
- In El Goonish Shive, Grace only found out her birthday and exact age a short while before turning eighteen. Thanks to being a part-alien hybrid created in a corporate laboratory she'd never been told her exact birthday before.
- Bob's Burgers: The premiere episode "Human Flesh" reveals that Bob is so absent-minded about dates he not only forgot Linda's birthday once, but his own.
- The Transformers: One episode reveals that Ultra Magnus doesn't remember the date of his own creation so Wheelie and Daniel set out to find it.
- Harvey Beaks: Because they lost their parents at a young age, Fee and Foo don't know when their birthday is, and have never had a birthday party. Harvey attempts to throw them the best "first birthday" he possibly can in "Fee and Foo's First Birthday".
- Steven Universe: In "So Many Birthdays", Steven finds out the other Crystals Gems Never Had a Birthday Party. As Garnet and Pearl were born on another planet, Amethyst lived alone for a long time, and all of them predate modern calendars anyway, Steven just decides to act like the current date is all three of their birthdays.
- She-Ra and the Princesses of Power: "The Sword, Part 2" implies Adora doesn't know her birthday, because thanks to her sheltered upbringing in the Horde she doesn't understand the mere concept of birthdays.
Bow: No birthdays? How is your life this sad?!
- PJ Masks: In the short "PJ Masks Surprise", the PJ Masks throw a birthday party for An Yu. Since she has been trapped in the dragon gong for centuries, and hardly ever leaves Mystery Mountain, she doesn't understand what a birthday is.
- During the Futurama episode "Bender Should Not Be Allowed On Television", Cubert — thinking how fun it'd be to have a birthday party — realizes that he doesn't technically have a birthday on account of being a clone of Professor Farnsworth. Fortunately for him, his folks decide to give him one anyway, either based on the day he was extracted from the cloning tank or the day his DNA was first extracted from the Professor (Cubert chooses the latter).
- Mosuo writer Yang Erche Namu does not know her own birthday, as Mosuo traditionally do not record them.
- Technically the case for anyone who was a foundling (excluding those who had obviously been born the same day they were abandoned); they do have a official birth date but usually it's just an educated guess in order to have something to put on the paper work that's based on how old they're estimated to be when found.
- Tenzing Norgay initially didn't know his birthday, he just knew it was in late May. After climbing Mount Everest with Sir Edmund Hillary he decided to celebrate it on that day, May 29.
- Boxer Sonny Liston did not know precisely when he was born. He believed it was May 8, 1932 and used this as his official date of birth, but researchers have concluded that he was most likely born two years earlier, with July 22, 1930 mooted as one of the most likely dates.
- May occur if someone is born in a remote area that doesn't keep up-to-date on the current Gregorian date because it's not easy to contact or travel to that location. The date the paperwork is physically filed with the nearest administrative office can end up being used as the official birthdate, even if that's several months after the day the baby was actually born.