Birthdays are celebrated in the Animal Crossing series by both the player and animal villagers. The player can choose their birthday when asked by a villager early on in game, or by Timmy and Tommy in New Horizons. Any date can be chosen for the player's birthday. In Wild World or City Folk, if a date is selected that either is the same as that villager's birthday or the current day, the animal will realize this and appear shocked. Birthdays of special characters cannot be celebrated.
In the games
In Animal Crossing
When the player leaves their house, they will be greeted by a random villager, not necessarily their best friend. The villager will wish the player a happy birthday, and give the player a present. The player will also find letters and presents in their mailbox from other villagers also wishing that player a happy birthday, including a birthday cake from Mom. However, the item can't be eaten; it can only be displayed in the player's house.
In Wild World
Wild World is the first game that introduces villagers birthdays. The player can visit them in their house on that day, where they will be walking around their home with another villager. On a villager's birthday, the villager will wake up an hour later than normal. The player can give any item to the villager that is celebrating their birthday as a gift. They will then give the player something in return. A player can tell if it is a villager's birthday by a letter that is distributed by the animal, and a notice that appears on the bulletin board on the day.
The player themselves will receive a birthday cake on their birthday, which can only be displayed once again. The player will also receive letters presents from their mother and all other villagers.
In City Folk
Unlike in Wild World, villagers do not celebrate their birthdays, despite a notice on the bulletin board that congratulates them. Instead, a player can send the villager a letter on that day. The villager then thanks the player for wishing them a happy birthday in their reply.
As with Wild World, the player is presented with a cake on their birthday by a villager. In this game, the player has the option to eat the cake. If they do, they will blush and flowers briefly blossom from them. The player's mailbox is also full of letters wishing the player a happy birthday. Each letter is from a villager: the player gets a letter from each villager in their town except the villager that delivered their birthday cake. Mom sends the player a letter that contains 5,000 bells.
In New Leaf
“Today is your birthday isn't it? Happy birthday!”
― Isabelle at spotlight, upon first load on the player's birthday.
Similar to City Folk, a random villager, or in New Leaf's case, the villager who is best friends with the player, will be waiting outside the player's house. However, in New Leaf, they will proceed to invite the player to their house for a surprise, revealing two other villagers and a large birthday cake in the center of the room. They will shout "Happy Birthday!" upon entering. When pressing "A" in front of the cake, the villagers will tell the player to make a wish. The candles can then be blown out by blowing on the Nintendo 3DS. Once blown out, the villagers will let off party poppers and begin clapping. The host villager will then give the player a gift of an item from the Birthday set.
If the player's birthday does not fall on a Saturday, K.K. Slider (as DJ K.K.) will play a remix of K.K. Birthday in Club LOL after 8 PM. There are two versions depending on if he is playing the House Mix or the NES Mix.
For a villager's birthday, the villager will send a letter a week from their birthday to announce the event. On the actual day, they stay in their house with one other villager. When the player comes in, the villager will greet them, and if they talk to the villager, they can give the villager a present. They will continue celebrating for the rest of the day. Their house will have cake, furniture, and a CD Player with K.K. Birthday.
If a villager lives in the player's town with the same birthday as the player and they visit the party, they will make note of that.
In amiibo Festival
Birthdays of various characters can be celebrated in the Board Game mode; Player birthdays are a special event that can be celebrated by landing on special birthday event squares, while all other villager birthdays can be the subject of a random event that happens that day.
In New Horizons
Like New Leaf, the villager the player has the highest friendship with will be standing outside of the player's house. If the highest friendship is tied for two or more villagers, the game will do a random tiebreaker. They will take you to their house for a surprise, revealing two other villagers and a birthday cake in the center of the room, which is decorated with a birthday sign and a stereo playing K.K. Birthday.
The player is then invited to blow out the candles on the cake by pressing A. Afterwards, the player is given a present containing Birthday Candles. Then, the player is given a pinata stick and is told to hit the pinata (which has replaced the cake at this point and hangs in the center of the room). After breaking it, you are given up to ten Birthday Cupcakes, which can be given to the other villagers who didn't attend your birthday party in exchange for birthday set items. Birthday cupcakes can also be given to villagers who did attend your party, and they will have unique dialogue acknowledging that they attended.
K.K. Slider will be in the town plaza during the day of the player's birthday as well and will play K.K. Birthday. If there is an event happening during a birthday such as a Bug Off, then K.K. will instead appear on the following day. The player's online friends can visit an island the previous Saturday to write birthday messages by talking to K.K. Slider. These messages will be shown during the playing of K.K. Birthday. If the player doesn't have this happen, then villagers from their town, as well as two special characters, will do it.
Double birthdays are celebrated in Animal Crossing: New Horizons when two villagers living on the player's island have the same birthday date as each other.
A double birthday is very similar to a regular villager birthday celebration, but the two birthday villagers will have a shared party in either one of their houses. Both villagers wear the Birthday Hat and will talk about how surprising it is that they share a birthday with another villager. The player can give a present to both of the birthday villagers.
“Happy birthday! Starting your job as mayor, and moving, and having your birthday all in one day...”
― Isabelle after player puts their birthday on the same day as the day they become mayor, New Leaf