How many points do you need to win a men's single match in badminton?

Badminton matches scoring goes up to 21 regardless of whether the game is singles, mixed doubles, mens or womens doubles. However the game can only be won only when the player is two points lead of the other player and a permissable score up till a maximum of 30. 21 points limit can only be disregarded only when trying to attain a 2 points lead. Examples:

21-19 is a winning score

21-20 not a winning score; but 22-20 is; However

30-29 is a winning score

22-15 is a non-permissable score; 21-15 is enough to win the match