When to Double in Backgammon

Things just go better in twos. That is why Little Caesars has a little cartoon Roman running around in its commercials yelling "Pizza Pizza!" at anyone who even looks vaguely interested. Doublemint gum has employed twins who look the Olson sisters to stroll around town in matching outfits trying to convince us to chew gum. Yes, in a world where "two for one" burgers at Rally’s gets us going, is it any surprise that doubling is an option in backgammon?

The first big decision when thinking about doubles is exactly when you should offer one. In fact this is a far more difficult decision to make than whether or not to accept the double when it is offered to you.

The decision of when to offer a double is always more difficult than the decision of whether to accept or refuse. The general problem with deciding when to extend this offer is centered around how much a position's value is likely to change in the next roll or two. Your situation, and fortunes, in the game may change considerably from one chance to double to the next.

The best time to double is at the top of your market, when it would be correct for your opponent to either accept or refuse, but this will happen about as often as you catching a Sasquatch rummaging through your garbage bins. The next best options are to either double early (when your opponent should accept), or late (when your opponent should refuse).

When you find yourself very close to the top of the market window, it is almost certainly correct to double. Of course, if you are beyond the opponent's drop point, you should definitely double and take the sure point (unless there is a significant chance of a gammon). But what about before the opponent's drop point, while the opponent still has a clear take?

Ask yourself if there is a cost associated with any double which is not made at exactly the top of the market window. The act of doubling early gives your opponent the cube at a time when they still have a good chance of using it against you. When you double late, you are not getting the most out of your double.

The early/late cost ratio compares the cost of doubling early with the cost of doubling late. When the early/late cost ratio is low, you are more willing to double early to avoid the possibility of overshooting the opponent's drop point by a significant amount. When the ratio is high, you prefer to be very close to the opponent's drop point before offering a double.

The rule of thumb suggests that it is better to double early (while you still have a take) than to double late. This is especially true when playing from behind in the match, and most particularly when the opponent is only two points away from winning.

For example, if you are behind in a match at 6-away, 2-away. The ideal time to offer a double is when you have about a 70 percent chance of winning the game. Actually, though, it turns out you can afford to double much earlier than this with very little cost. The early/late cost ratio at this score is so low (only 0.2), that you should double earlier than that 70 percent mark than risk the possibility of having your double refused.
When you are well ahead in the match, you must be more careful about doubling early. You want to wait until the point where you have a good chance of overshooting the market by a significant amount if you do not double now.