Game and Slam Odds

Each row of the table sets bidding on against stopping one step lower, and gives the chance of success at which the two choices come out level over many deals. The number most players want is the vulnerable game, which needs only 37.5 percent to be worth bidding at IMPs.

Every row weighs two outcomes on the IMP table. Take 4♠ vulnerable against stopping in 2♠. When ten tricks make, the game scores 620 and the part score 170, a gain of 450 or 10 IMPs. When only nine make, the game goes one down for minus 100 while the part score would have taken 140, a loss of 240 or 6 IMPs. Bidding the game breaks even when it makes 6 times in 16, which is 37.5 percent.

The level you stop at makes no difference to the bar. Stopping in 3♠ and making ten tricks scores 170, the same as stopping in 2♠ and making ten, so the gain and the loss are unchanged whichever part score you stop in. What moves the bar is vulnerability and the size of the bonus at stake.

Not vulnerable the gain shrinks to 6 IMPs and the loss to 5, so game needs 45.5 percent. A small slam needs 50 percent at either vulnerability, because the slam bonus gained and the game score lost come to about the same number of IMPs. A grand slam needs 56.0 percent not vulnerable and 56.7 vulnerable, since going down in seven throws away a small slam that was already made.

Players call a vulnerable side red and a non-vulnerable side green or white, after the colors on the boards. So a red game is the one to bid on 37.5 percent, and a green or white game wants 45.5.

At matchpoints none of this applies in the same way. Each board is ranked against the field, a game is a gain only when it beats the tables that stopped lower, and the break-even sits at roughly 50 percent for every decision in the table.

At teams, bid the vulnerable game when it is close. A game that depends on one of two finesses is comfortably over 37.5 percent. Slams need an even chance, and a grand that rests on a single finesse is a losing bet. Before a slam, use Blackwood to check the aces, and see hand evaluation for judging when the values are there. The scoring guide covers the bonuses behind each row.

What percentage do you need to bid a vulnerable game?

At IMPs a vulnerable game breaks even at 37.5 percent. Bid it whenever it makes more often than that.

What are the odds needed for a non-vulnerable game?

About 45.5 percent at IMPs. The smaller game bonus not vulnerable makes the gain from bidding it smaller.

When should you bid a grand slam?

When it makes about 56 percent of the time or more at IMPs, 56.0 not vulnerable and 56.7 vulnerable. A grand that needs a single finesse falls short.

Are the break-even odds different at matchpoints?

Yes. At matchpoints the break-even is roughly 50 percent for games and slams alike, because each board is ranked against the field rather than scored by the size of the swing.