What is Duplicate bridge?
The standard game here is rubber bridge: the partnerships play deal after deal until one side has won two games, and good cards win a lot of points. Duplicate bridge keeps the auction and the play exactly as they are, but every deal is a numbered board that is scored on its own, and its result is compared with the result of the same cards played at another table. A side that holds poor cards can still win the board by losing less than the other table did, so the luck of the deal counts for much less.
Before the match you choose how many boards to play: 4, 8 or 16; the default is 8. North deals board 1, East board 2, South board 3 and West board 4, and the cycle repeats. The vulnerability is fixed by the board number, in the cycle clubs use: on board 1 nobody is vulnerable, on board 2 North-South, on board 3 East-West and on board 4 both sides; boards 5 to 16 shift that pattern by one place every four boards, so over sixteen boards each side is vulnerable on eight.
Scoring follows the duplicate tables. Trick points, overtricks, slam bonuses, undertricks and doubled or redoubled contracts score as in the standard game. There is no rubber and nothing carries over from one board to the next: a contract that makes earns a bonus of 50 for a part score, or 300 for a game, 500 if the declaring side is vulnerable. Honours are not scored, the same as in the standard game. If all four players pass, the board scores nothing and the next board is dealt.
There is only one table of players here, so the second table is played by bots. They hold the same four hands, and as in a match between two teams of four, each partnership's teammates sit the other way round there: the bots playing your cards stand in for your opponents' teammates. The difference between the North-South scores at the two tables is turned into IMPs (international match points) on the standard scale: 0 for a difference of up to 10 points, 1 for 20 to 40, 2 for 50 to 80, and so on up to 24 for 4000 or more. The IMPs go to North-South if they scored more at your table than the bots holding their cards did at the second table, and to East-West otherwise. After the last board the team with more IMPs wins the match; equal totals are a draw.
The second-table bots are simple. Each partnership's bot looks at its two hands together and picks one contract, the stronger side declares, the other side passes and nobody doubles, so a board is never passed out there. In the play each bot sees only its own hand, dummy and the cards played. Across many random deals they make roughly 69 percent of the contracts they declare, well short of perfect play, so a good result against them is a casual comparison, not a team match. The same cards always give the same second-table result, and that result is saved with the game, so a replay shows both tables exactly as they were.
Rule changes
| Rule | Standard Bridge | Duplicate bridge |
|---|---|---|
| Length of a match | Standard BridgeA rubber: deals go on until one side has won two games. | Duplicate bridgeA fixed number of numbered boards: 4, 8 or 16, chosen before the match; 8 by default. |
| Vulnerability | Standard BridgeNobody is vulnerable at the start; a side becomes vulnerable once it wins a game. | Duplicate bridgeFixed by the board number: nobody on board 1, North-South on board 2, East-West on board 3, both on board 4, then the standard cycle up to board 16. |
| A passed-out deal | Standard BridgeNobody scores and the next player deals. | Duplicate bridgeThe board scores nothing at your table, still counts as one of the boards and is compared with the second table. |
| Part scores | Standard BridgeTrick points below the line add up from deal to deal until a side reaches 100 and makes a game. | Duplicate bridgeEach board is scored on its own: a part score earns its trick points plus a bonus of 50, and nothing carries over. |
| Bonus for a game | Standard BridgeNone for a single game. The side that wins the rubber scores 700, or 500 if the other side has also won a game. | Duplicate bridgeEvery game made scores 300 at once, or 500 if the declaring side is vulnerable. There is no rubber bonus. |
| What a deal is worth | Standard BridgeIts points, added to the side's total. | Duplicate bridgeThe difference between your table's North-South score and the score of bots playing the same cards at a second table, with the directions swapped as in a team match. |
| IMPs | Standard BridgeNot used. | Duplicate bridgeEach board's difference is turned into 0 to 24 IMPs on the standard scale, credited to the team that gained on it. |
| Who wins | Standard BridgeThe side that wins two games wins the rubber. | Duplicate bridgeAfter the last board, the team with more IMPs: North-South or East-West. Equal totals are a draw. |
| Players | Standard BridgeFour in two partnerships; with two players the table plays a two-handed version. | Duplicate bridgeExactly four, North-South against East-West. A table of two always plays the two-handed game, scored as a rubber. |
History
The duplicate idea is older than bridge. It began with whist, where the same deals were replayed at another table to cut down the part luck plays. A whist game organised in 1857 by Henry Jones, the card writer known as Cavendish, set out to show how much that reduced the luck of the cards and let the better players come out ahead. Early duplicate whist was slow and mistakes were easy to make. Once the trays that keep each hand intact from table to table, now called boards, were much improved, the game spread, and by the 1890s it was widely played. When contract bridge took over from whist, duplicate bridge took over from duplicate whist.
Clubs and tournaments now play under a common code, the laws of duplicate bridge, issued by the international body for the game and its national members. The laws set the dealer and vulnerability printed on each of boards 1 to 16, the duplicate scores and the IMP scale. The scale used here is the one revised in 1962, which is still the one in the laws.
In a team match, each team of four splits into two pairs that sit in opposite directions at two tables, so both tables play every board and the net difference is converted into IMPs. The scale compresses large differences, so a big swing counts for less than its raw points. Pair events are usually scored by matchpoints instead; this page plays the team form. Here the second pair of each team is played by bots, which is this site's way of offering a duplicate comparison at a single table.