Doubling Cube Tips

When to refuse the Cube:

If you are cubed your opponent is telling you he thinks he will win this game. However, some cubes can be bluffs or a mistake by your opponent, while others should be taken if you still have 25% or more winning chances in the game. So take a general look around the board and base your decision on “Am I winning or losing? By how much? And, how can I win this game?”
If you appear to be in a position with considerable risk of losing a gammon (twice the wager) or even possibly a backgammon (triple the wager) reject the cube.
If your opponent is well ahead in the race (pipcount) and you will need to roll something like double fives or double sixes to catch up, don’t be too optimistic about your luck, just drop the cube.
If you have been hit and have one or more checkers on the bar and your opponent has two or three points made in his home board, and especially if he has other checkers (builders) that are threatening to make other blocking points, usually, unless you are well-anchored with two of your checkers on at least one of your opponent’s home board points, you should reject the cube.
If your opponent has a very strong home board, such as with 4 or 5 points made, and you have no anchor in his home board and you have one or more checkers that have been hit, or at high risk of being hit, in most cases, it is correct to refuse a double.

These are very basic scenarios. Backgammon doubling positions can be very complicated. Many players of the best players in the world save their doubling positions and study them with a program like GNUbg.

When to offer a Double:

Firstly, if behind in the score of a match, always remember to double your opponent before your first roll in post-Crawford games. Obviously, if you are ahead in the race, you should double - but how much ahead should you be?

One rough guideline is that you should be at least a full dice roll ahead of your opponent in the pipcount and in backgammon it is considered that 8 is the average value of a dice roll. For example, in the position below, Red is on roll and has a pipcount of 86 compared to White’s 95. Red is 9 pips ahead and will be further ahead after his next roll - Red should double and White, in this position has a take:

doubling position

We can also check this with another guideline called the 10% Doubling Rule, which says that if you add 10% to your pipcount and the result is not more than two pips higher than your opponent's pipcount you should double. In the case above, add 10% to Red’s 86 for 8.6 pips more equals 92.6 which is well under two pips higher than White’s 95 - you should double. If you already own the cube, the rule also says you should re-double if the result is not more than one pip higher.

Although the above position is at a point where it will become soon become a pure race, when considering to double in other types of positions where contact (the hitting of checkers) is still possible, study the board and base your decision on your answers to these questions:

In general, who has the better-looking board?
Do I have more home board points made than my opponent?
Do I have a prime (blockade) happening, and how does it compare to that, if any, of my opponent?
How many of the 36 possible rolls of the dice will improve my position on the next roll?
What threats do I pose to my opponent’s checkers on the next roll?
Do I have my opponent in a position that is too good to double and I should just play on for the gammon?