Under the Jacoby rule, a gammon or backgammon counts as a single point unless the doubling cube has been turned at least once. It is one of the most commonly misunderstood conventions in the game, mostly because people assume it is a rule everywhere. It is not.
Without the Jacoby rule, a player who is winning heavily has a reason to avoid doubling: they can quietly play on for an undoubled gammon and collect two points while their opponent has no way to end the game. The Jacoby rule removes that incentive by making the extra point worthless until someone turns the cube. Win a gammon with the cube untouched and you score one point, exactly as if it were a plain win.
It is a money play convention. It is standard in most online money games and many club money sessions, and it is not used in match play, where the score already governs the value of gammons and no such distortion exists. If you are playing a match to seven points, the Jacoby rule is simply not in effect, whatever an app's settings screen may imply.
The practical effect is that it pushes the cube out earlier. If you have a strong position with real gammon chances and the cube has not moved, those gammon chances are currently worth nothing to you, so the argument for doubling now is stronger than it would otherwise be. Players who learned without the rule tend to sit on winning positions far too long when they start playing with it.
They are named after different people, solve different problems and apply in different formats. Crawford applies in match play and makes one specific game cubeless after a player reaches match point. Jacoby applies in money play and devalues undoubled gammons. Confusing them is common, and it leads to people claiming the cube is dead when it is not.
Money sessions that use the Jacoby rule frequently allow beavers as well: a player offered a double may accept and immediately redouble to four while keeping the cube. It is a separate agreement, not part of the Jacoby rule, but the two appear together often enough that it is worth confirming both before a session rather than discovering the difference mid-game.
The Jacoby rule is one of the official rules of backgammon.
It is an optional convention for money play, and it does not apply in match play at all. Plenty of people have argued about a gammon being scored as one point in a tournament match because they learned online with Jacoby enabled and assumed it was universal. Agree the format before the first roll: whether the Jacoby rule is on, and whether beavers are allowed, are both things to settle in advance rather than afterwards.
Play a rated game and every decision gets reviewed afterwards against the best move available. The dice are committed before you roll and checkable after, so the number you end up with is a measure of you, not of luck.
Play a rated game freeA money play convention under which gammons and backgammons count as a single point unless the doubling cube has been turned at least once during the game.
No. It is used in money play only. In a match to a fixed number of points the score already determines what gammons are worth.
Crawford is a match play rule making one game cubeless once a player reaches match point. Jacoby is a money play convention devaluing undoubled gammons. They apply in different formats and solve different problems.
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