In badminton, a game tied at 20 points each is at deuce.
At 20–20, a player or pair must gain a two-point lead to win the game. This means the score can continue beyond 21, unlike an ordinary game that ends when a side reaches 21 with the required advantage.
There is also an absolute limit: if the score reaches 29–29, the side winning the next rally wins the game at 30–29. This rule prevents an endlessly extending game while preserving the importance of a two-point margin in most late-game situations.
The rally-point system awards a point after every rally, regardless of which side served. A match normally consists of the best of three games.