Doubling cube strategy
When to double, when to take, and when to pass: the numbers behind the cube.
This guide assumes you know how the cube works: who can double, and what taking and passing mean. If not, start with Match play. The numbers below are for a money game, a single game played for a stake, which is the standard way to learn the cube. Matches shift them, as the last section explains.
Taking: the 25% rule
When you're doubled you choose between two outcomes. Pass, and you lose the current stake. Take, and you play on for twice as much.
Suppose you'd win this position one time in four. Over four games, passing every time costs you 4 points. Taking every time, you lose three games at 2 points and win one at 2: a net loss of 4. So 25% winning chances is the break-even point. With better chances than that, taking loses less than passing.
Owning the cube after you take pushes the real take point a little lower, because you can redouble if the game turns your way. Gammons push the other way: a position where you'd often lose a gammon needs better chances to take.
Doubling: timing is everything
A double is right when you're a clear favourite but your opponent still has a take. As a rule of thumb, that's around 70% winning chances in a money game, and earlier in volatile positions that can swing on a single roll.
The risk of waiting is losing your market: if a good roll next turn would leave your opponent with an easy pass, you've missed the moment to double while they'd still take. Positions with a lot of hitting and shots lose their market fastest, so double those a little earlier.
Too good to double
If your opponent should pass but you have strong chances of winning a gammon, don't double. They'd pass and give up 1 point, when playing on might win you 2. Keep the cube where it is and play for the gammon; double later if the gammon chances fade.
In a race: count your pips
Once contact is broken, the game is a race, and the cube decision comes down to the pip count: the total number of pips each side needs to bear off.
To count, multiply the number of checkers on each point by that point's number and add them up. A checker on the bar counts 25. At the start of the game both players need 167 pips.
The 8-9-12 rule
For longer races (around 100 pips or more), work out the leader's lead as a percentage of the leader's own pip count:
- A lead of about 8% is enough for a first double.
- A lead of about 9% is enough to redouble.
- The trailer can take while behind by up to about 12%, and should pass beyond that.
For example, if you need 100 pips and your opponent needs 110, your lead is 10%: a good double, and a take for them.
The rule is a rough guide. Short races and bear-offs with gaps or awkward stacks behave differently; experienced players use more precise counts, such as the Keith count, for close decisions.
The cube in match play
In a match, what matters isn't points but your chances of winning the whole match, so take points and doubling points move with the score. Serious match players look these up in a match equity table. A few landmarks:
- The Crawford game. The cube is out of play for the one game after a player first comes within a point of winning the match.
- Post-Crawford. After the Crawford game, the player who's behind should usually double at the first chance. Their opponent needs only one more point, so a bigger stake costs the trailer nothing extra.
- Gammons change value. If a single win at the current cube value would already win you the match, a gammon adds nothing, so play safe rather than chase one. When you're well behind, gammons count for more, because you need the extra points.
The full rules for matches, the Crawford game and the Jacoby rule are in Match play.