Ninety-nine is a simple card game based on addition and is reportedly popular among the Romani people. It uses one or more standard decks of Anglo-American playing cards in which certain ranks have special properties, and can be played by any number of players. During the game, the value of each card played is added to a running total which is not allowed to exceed 99. A player who cannot play without causing this total to surpass 99 loses that hand and must forfeit one token.

Due to the simple strategy and focus on basic addition, the game is ideal for culturing math skills in children. This is also true because the new total must be called out on each play, lending enjoyment to more expressive children and assertiveness practice to others.

At the start of the game, three tokens are distributed to each player. Each hand, three cards are dealt to each player, and the player to the left of the dealer takes the first turn by choosing one of the cards in their hand, places it on the discard pile, calls out its value, and then draws a new card. The player to the left then chooses one of their cards and places it on the discard pile, adds its value to the previous card and calls out the new total. If a player forgets to draw a new card before the next player plays, that player must remain one card short for the remainder of the hand. Play proceeds in this manner until a player cannot play without making the total value exceed ninety-nine. That player loses the deal and must turn in or discard one of their tokens, after which all cards are then collected and a new hand is dealt. Once a player runs out of tokens, that player is out of the game. The last player remaining, i.e. the last player with the token(s), wins the game. A variation uses dollar bills or pieces of paper instead of tokens. Each time a player loses the deal, their dollar bill is folded. Five folds are allowed: all corners, then in half, after which that player is out. The last player remaining wins and takes all the dollar bills.