Doubling Gin is a version of Gin Rummy that provides an opportunity for a bit of bluffing and gamesmanship.
The concept works similarly to the doubling cube in Backgammon - before drawing a card, a player may challenge his opponent to double the points for the hand.
If the opponent declines the double, then the hand ends immediately, as if the doubler (the one proposing the double) had knocked (regardless of his actual deadwood count). The doubler wins the hand immediately, then scores a 10-point bonus, plus any positive difference in the deadwood count. The loser cannot undercut the winner, no matter the difference in deadwood count. Score for the hand is multiplied by the doubling factor in effect at the time of the refusal.
However, if the opponent accepts the double, points for that hand are doubled, and play proceeds as usual.
This doubling may go on and on as long as the players have the nerves for it (or to a predetermined doubling limit, if so desired). Either player may offer the first double; thereafter the right to double alternates.
Should the hand end normally (i.e. with a knock), then points for the hand are calculated normally, with any gin or undercut bonuses added. The net score is then multiplied by the doubling count (2, 4, 8, etc.) for that hand. Box bonuses and shutout bonus are not subject to the doubling, since they are not part of the hand.
Doubling Gin is typically played to 200 points.