If you want to emphasize that your character is somehow "different" from everyone else, you can underline this by giving him/her a physical deformity; one of the most popular options is extra digits. The reason for this choice is simple: unlike many other deformities which look "obviously wrong" and therefore repulsive at first sight, a sixth finger or a toe may look perfectly normal and not be noticeable unless one deliberately counts them.
Depending on the Writer, it can be either an obvious defect (probably symbolizing covert malignity of the person) or a Charm Point emphasizing how adorably unconventional the character is. It may also serve a functional purpose: with extra digits, the character may be able to do something no one else can (like playing certain piano compositions). Often, it is relevant to the plot because it reveals that a character is secretly related to another character with the same trait, or it otherwise says something about their ancestry. It can also serve to distinguish the character if a description of them is necessary: if you're looking for a six-fingered man, it's easier to just say that than to describe features such as age and hair color that could apply to lots of people.
Non-human entities, animals and monsters do not qualify for this trope, with the exception of human-like species who are only distinguished from humans by a different number of digits.
Not to be confused with Alternative Number System, though a race with a different amount of digits is likely to use one.
- A well-known blooper in the 1957 Hornby-Dublo catalogue: the father is drawn with an extra finger.
- The Pattersons' neighbor Anne Nichols from For Better or for Worse has three children. The youngest, Leah, was born with six fingers on both hands. Anne has the extra fingers surgically removed shortly after birth.
- In Bruce Almighty, Bruce has God say how many fingers he has extended behind his back so the latter can prove his identity. At one point Bruce tries to pull a trick where he initially extends seven fingers (all five on his right hand and two on his left) only to abruptly close the two fingers on his left hand. God says seven, and Bruce holds up his right hand with a smug "Hah!", only to see that his right hand suddenly has seven fingers. The extra fingers immediately disappear after Bruce frantically shakes his hand around.
- In Gattaca, the protagonist and his girlfriend at one point see a concert by a pianist who was genetically engineered to have twelve fingers. There are apparently enough people like this around that some pieces of piano music require extra fingers to play.
- Douzi from Farewell My Concubine was born with a sixth finger. At the beginning of the film, his prostitute mother begs the opera school to take him, and when they refuse due to his sixth finger, she drags Douzi out into an alley and chops it off with a cleaver. She then drags him back, they take him, and she's never seen again.
- In The Chrysalids, Sophie has six toes on both her feet, which is a major plot point.
- In The Secret of Castle Cant, the protagonist Lucy also has six toes on her feet. This is a sign of her royal ancestry.
- In The Jewel of Seven Stars, Queen Tera was born with seven fingers on one hand and seven toes on one foot; that's why the number had a mystical meaning for her.
- In Hannibal, the eponymous villain has six fingers on his left hand, as a metaphor for "being a monster". He uses this to his advantage when hiding an improvised handcuff key in his right hand, knowing the officer's attention will be on his unusual left hand.
- In both the book and film versions of The Princess Bride, the evil Count Rugen has six fingers on his right hand, and a sword specially made to be usable with his extra digit plays a significant role in the plot.
- In A Song of Ice and Fire, King Aegon II Targaryen's son Jaehaerys had six fingers on his left hand and six toes on each foot due to the Targaryen family history of Royal Inbreeding.
- Jack, the titular character of The Twelve-Fingered Boy, who also has psychic powers.
- The Contortionist's Handbook is about a talented young forger with six fingers on his left hand, a handicap considering he constantly changes his identity in order to escape discovery.
- In A Clockwork Fairytale, members of royalty are identified by having six toes on their feet; this is how the protagonist understands that Melba is the missing princess.
- In A Brother's Price, part of the Porter family is polydactyl, with an extra toe on one foot. This tips off Eldest Whistler to the paternity of Kij's daughter, Eldie, who was sired by Kij's brother Keifer. While Keifer was married to the princesses.
- In Neil Gaiman's short story "How to Talk to Girls at Parties" one of the girls has an extra finger, by which she notes her alien culture prohibits her from reproduction because it's a defect. The protagonist, who is just trying to get off with someone, ignores the context and just notes the finger as an interesting feature.
- In Across a Billion Years by Robert Silverberg, the protagonist's Love Interest Jan Mortenson has six toes on both feet, 40 teeth, and some other minor differences from humans due to being a half-blood (three-quarters human and one quarter alien). The protagonist sees this as a Charm Point.
- In Tales of Three Lands series by Linda Smith, there are two very similar races: the Uglessians and the Freyans. The Uglessians' only difference is that they have magical abilities and six-fingered hands.
- In All the Fishes Come Home to Roost: An American Misfit in India, the beautiful Indian piligrim Freyni Dadachanji has six toes on both of her feet.
- In Alice, Girl from the Future, Iria Gai has 6 toes on her feet because she is actually an alien from the planet Vester (this planet's inhabitants are distinguished from humans by their lilac eyes and 12 toes).
- On the Warrior Cats official app it is noted that Blackstar has six toes on one paw.
- Redwall: Outcast of Redwall's Swartt Sixclaw has six claws on his left paw.
- On Barrayar, accusing someone of having extra digits is regarded as a major insult, due to their cultural horror of mutations and deformities.
- In the Darkover series, some humans who have chieri ancestors have five fingers plus a thumb on their hands, as do the chieri themselves.
- Lilith's Brood: The Cthulhumanoid alien Oankali have sixteen fingers and two thumbs on each hand, thanks in part to their ongoing genetic manipulation of themselves as a species. Humans tend to find the arrangement creepy, but not nearly as much as their Eyeless Faces and anemone-like tentacles.
- One season finale of Empty Nest has Harry, Carol, and Barbara going to England for a family ceremony. Just before they leave, Barbara mentions Carol having been born with eleven toes. When they get to the castle, they meet a butler who also has eleven toes. Later, Harry gets lost in the dungeon and stumbles upon a skeleton who also has eleven toes.
- A parody commercial from Saturday Night Live advertises a finger removal cream for people with extra fingers.
- The Outer Limits (1963) episode "The Sixth Finger". When a man experiences accelerated evolution, he develops an enlarged head and a sixth finger on each hand.
- One episode of The X-Files starts with a girl who's shown to have six toes on her feet. The case becomes about the mysterious deaths of several girls (including this one) born with six digits on all four limbs (some had the extra fingers removed to better fit in).
- Star Trek: Enterprise once mentions Nuvian masseuses, who have twelve fingers. On each hand.
- In Clandestiny, Andrew has "the mark of the MacPhiles", which is six fingers on each hand.
- In Fallout 2, the Chosen One can mutate a sixth toe from spending long enough in toxic waste unprotected. Having one will result in failing the physical of the Vault City citizenship test, unless it is amputated by an Auto Doc and acquired as an item.
- In Umineko: When They Cry, Kinzo has six toes which is used to identify his corpse. They're also shared by his bastard child Sayo Yasuda/Lion Ushiromiya, who had them amputated to try and hide their true identity after they were assumed dead, but it left scars that Kinzo noticed and clued him in to their relationship. Interestingly none of Kinzo's legitimate children seem to have inherited this trait, which may or may not be because Kinzo was Sayo/Lion's father and grandfather.
- Aunt Ruth from the The Loud House episode, "Two Boys and a Baby" is revealed to have an eleventh toe.
- In Gravity Falls, the author of the journals, Stanford Pines, has six fingers on each hand.
Mabel: Woah, a six-fingered handshake! It's a full finger friendlier than normal!
- In Clarence, Jeff has an extra toe that he's self-conscious about. When Clarence learns about this, Jeff becomes very worried that his secret might get out.
- Billy, the elderly giant barbarian hero from Adventure Time, has 6 fingers on each hand.
- The Blue Meanies from Yellow Submarine have six-fingered hands to emphasize their overall evilness.
- Zigzag the Grand Vizir in The Thief and the Cobbler has six fingers on each hand, perhaps to show that he's a master manipulator.
- Done as a gag on the Tex Avery MGM Cartoon "The Hick Chick". A chicken complains that her dance partner has twenty toes, a '40s slang term for a bad dancer. Naturally, Avery takes the line literally, showing the rooster with ten toes on each foot (and human feet as well).
- A similar gag was done in "Billy Boy", where the titular goat eats off the farmer's shoe. To his relief, he still has the ten toes on his foot.
- Glossaryck from Star vs. the Forces of Evil has six fingers and six toes. Like with many cartoon examples, it's weird because the other characters still have only four fingers.
- The Gem Fusion Lemon Jade in Steven Universe has six fingers on each hand, as well as four upper arms that merge on either side into two forearms.
- A whole family from Brazil who have six fingers and toes as an inherited genetic trait. They consider it a positive anomaly; in fact, it is the family members with regular number of digits who feel "left out".
- Another family in India has the same, but are less proud of it because prospective husbands of the daughters dislike it.
- Anne Boleyn was posthumously claimed to have had six fingers on one hand by Catholic propagandists who considered it a sign of witchcraft. One more neutral biographer claimed that people who knew Anne had told him that she had a split or duplicated fingernail on one finger, which may have been exaggerated into a sixth finger.
- The actress Gemma Arterton, one of the Bond girls, was born with six fingers on both hands (they were surgically removed shortly after). In her own words: "It's my little oddity that I'm really proud of it. It makes me different".
- Former MLB relief pitcher Antonio Alfonseca was known for having 6 digits on both his hands and feet.