Backgammon Equity

You will often hear backgammon players talk about equity. What is it? It is simply a rate - the rate at which a player expects to gain or lose per point, whatever stakes he is playing for.

• In an even game a player`s equity is zero; he expects neither to win nor lose in the long run.
• If a player is certain to win and he is playing for one unit his equity is +1. If he is certain to lose his equity is -1.
• If a player is certain to win a gammon and he is playing for one unit his equity is + 2. If he is certain to lose a gammon his equity is -2.
• If a player is certain to win a backgammon and he is playing for one unit his equity is + 3. If he is certain to lose a backgammon his equity is -3.
• In any situation the two players` equities sum to zero.
• All of the above is what is called `cubeless equity` - to get a player`s total equity for a position you need to multiply the cubeless equity by the value of the doubling cube.

What about if a player is 75% favourite to win a game - what is his equity? It is simply the difference between his winning chances and losing chances. In the 75% case that is 0.75 - 0.25 = 0.50.

This is a useful reference point in terms of equity. In any given position if a player`s equity is close to 0.50 he should at least be considering doubling and conversely the opponent whose equity is -0.50 (remember the two player`s equities always sum to zero) will know he might have to think about being doubled. Normally (and there are exceptions) the upper limit for a take is around - 0.550 equity.

The backgammon playing computers, Snowie, Gnubg and Jellyfish all use equity to provide information about the position that they analyse. The moves they recommend are the ones that, after analysis, give the highest equity for the position in question.

A player`s equity in a position can be very difficult to calculate (way beyond humans) because it is calculated by looking at all possible outcomes (the percentages of single games, gammons and backgammons) from a specific position and then doing the necessary calculations to calculate the equity.

From a human perspective we just need to understand the concept, not the calculations!

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