Doubling occurs during scoring and payments depending on the variations. Some rules have no doubling
When scoring in certain variations of mahjong, a player first adds up his basic points (for melds, flowers, winning bonus) and then doubles his score one or more times based on certain criteria. For example, in classical mahjong a basic hand with say a dragon pung and nothing much more will gain a couple points for the pungs a player may have, a point or two for a flower and a bonus of 10 points for winning. Lets say that this earns 16 points. These 16 points are the players basic points for winning. This score may now be doubled. Imagine the player had the dragon pung and the rest of his tiles are all bamboo. He will double his points once for the dragon pung and once more for having a clean hand (only bamboo with honour tiles). 16 doubled once will give 32. This will be doubled another time giving 64 points in total. The criteria for doubling depends on the variation of mahjong, special rules and the personal choice and variation of the players.
The above should not be confused with doubling when paying other players. Some variations have no sense of doubling points as shown above including Hong Kong mahjong and Korean rules. However, once the points are settled and the payment determined, some players may have to pay each other double.
In some variations the east player recieves or pays double. As well, during the round of the east, all points may be doubled.
Player who discards the winning tile
In some variations the player who discarded the winning tile may have to pay double to the winner.