Tools › Cube decision
Doubling-cube trainer
The cube is where matches are won and lost. Enter your winning chances and how often your wins and losses turn into gammons, and this trainer works out your take point, whether your opponent should take or pass a double, and whether you are too good to double at all — using the standard money-game formulas.
How it works
The calculator follows Rick Janowski's money-game model. Your gammon rates set the average value of the games you win (W) and lose (L): a clean win is worth one point, a gammon two. From those it computes your take point — the share of wins you need to accept a double — for a dead cube, a normal cube and a fully live cube:
- Dead cube: take point = (L − 0.5) ÷ (W + L). With no gammons this is the familiar 25%.
- Live cube: take point = (L − 0.5) ÷ (W + L + 0.5), about 20% with no gammons, because the right to redouble is worth something.
The take-or-pass verdict for your opponent is exact: it compares their winning chance against their own take point. The advice on whether you should double is a guide rather than a verdict, because a precise double also depends on volatility — how likely the position is to swing before your next turn. When you are very likely to win a gammon, the tool flags that you may be too good to double and should play on.
For the ideas behind the numbers, read the doubling cube, and use the match-equity lookup for cube decisions in match play, where the score changes the maths.
Formulas: Rick Janowski, Take-Points in Money Games, and Peter Bell, The Doubling Cube, both on Backgammon Galore. The model uses single wins and gammons; backgammons are left out for simplicity, so very high gammon rates are approximate.
Common questions
What is a take point?
The take point is the minimum share of winning chances you need before accepting a double is correct. In a simple money game with no gammons it is about 25% on a dead cube and around 20% when you can redouble, because owning the cube is worth something. Gammon risk pushes it higher.
When should I double in backgammon?
Roughly once you are a clear favourite and there is a real chance the position will swing away from you before your next turn — that risk of losing your market is what makes doubling pay. If your position is so strong that you are likely to win a gammon, you may be too good to double and should play on instead.
What does too good to double mean?
It means your position is worth more than the single point a double could cash, because you are likely to win a gammon or backgammon. Doubling would let your opponent drop for one point; playing on keeps the larger prize in view. It happens when your cubeless equity already exceeds one point per game.
How do gammons change the take decision?
Gammons enter the maths through the value of the games you win and lose. If the games you might lose are often gammons, taking is more dangerous and your take point rises. If the games you might win are often gammons, you have more reason to play on rather than cash, edging towards too good to double.