The doubling cube is what turns backgammon from a game of luck into a game of judgement. This guide explains how the doubling cube works, when to offer a double, when to take it and when to pass.
How it works
The cube starts in the middle at 1. Before rolling, you may offer to double the stakes. Your opponent either takes, and the game goes on at twice the value with the cube on their side, or passes and loses the game at its current value.
Only the player who owns the cube can redouble later. A gammon (mars) is worth twice the cube, a backgammon three times.
When to take: the 25% rule
If you pass, you lose 1. If you take, you play for 2: you lose 2 or win 2. Taking is better than passing when you win at least about 1 game in 4 (25%). That is a lower bar than most beginners think: many positions that look bad are still takes.
Gammons change this. If you might lose a gammon, you need more than 25%; if you might win one, you need less.
When to double
Double when you are clearly ahead but your opponent still has a fair chance: a race lead of about 8–10% (see the pip count guide), a strong attack against a blot, or a much better board.
Don’t double too late. If your opponent would pass, you get only 1 point. If you are so far ahead that you might win a gammon, playing on can be worth more: that position is called “too good to double”.
In a match: the Crawford rule
In a match, the cube helps the player who is behind. When one player gets within 1 point of winning, the next game is played without the cube (the Crawford rule). From the game after that, the player who is behind should double early, since they have nothing to lose by it.
The cube on ZAR
Online games on ZAR always use the cube. Against the computer and on one device you can switch it on or off. After the game, the review checks your doubles and takes too.