Backgammon Cube Calculator
The doubling cube is where matches are won. Stop guessing it.
Tap to add or remove checkers, or drag a checker to move it. Drag to the right tray to bear off.
The engine (~3 MB) loads on first analysis and then runs instantly in your browser.
Reading a cube decision
Most players lose more equity with the doubling cube than with their checkers, because cube errors are invisible: nothing on the board punishes you immediately for a missed double or a wrong pass. This calculator makes those errors visible. Set up the position, press Cube decision, and you get the verdict — double/take, double/pass, no double, or too good — alongside the three equities that produced it: the value of not doubling, of doubling and being taken, and of doubling and seeing your opponent pass.
The classic rules of thumb fall out of those numbers. A take is correct when taking loses less than the single point a pass concedes; a double is correct when your advantage is big enough that the cube pressure gains more than the flexibility you give up; and “too good” means your position wins so many gammons that playing on for two points beats cashing one. Positions near the borderline are exactly where humans misjudge — market-losing sequences, recube vigorish, gammon threats — and exactly where a calculator earns its keep. For checker-play fundamentals first, start with the opening reference.
Frequently asked questions
When should I double in backgammon?
As a first approximation: double when you are a clear favourite and your opponent still has a take, or when you risk losing your market — winning so much next exchange that the take disappears. The calculator’s equities replace the approximation with the actual answer.
What does “too good to double” mean?
If your winning and gammon chances are high enough, doubling lets your opponent escape for one point when playing on would often win two. The verdict appears when the no-double equity exceeds the double/pass value of +1.