There are several versions of this game, also known in the official rules as Four-Deal Bridge. As this name suggests it is a game for four players which is complete in four deals, unlike Rubber Bridge, where the length of a rubber is indefinite. This greater predictability has made it popular in some American clubs where Rubber was formerly played.
The vulnerability varies from hand to hand in a fixed pattern as follows:
Hand 1: Dealer North; neither side vulnerable
Hand 2: Dealer East; North-South vulnerable
Hand 3: Dealer South; East-West vulnerable
Hand 4: Dealer West; both sides vulnerable
The game bonus is 500 when vulnerable, 300 when not vulnerable. If a team makes a part score this is carried forward to subsequent deals until one side makes a game. A team which has an outstanding part-score at the end of the fourth deal scores a bonus of 100.
Note: the original version of Chicago had the vulnerability reversed in hands 2 and 3, so that the dealing side was vulnerable. The more modern scheme, which has the non-dealing side vulnerable as shown above, tends to lead to more competitive bidding.
Chicago with Duplicate Scoring
Chicago is sometimes played using duplicate scoring. There is no accumulation of part scores or games from deal to deal - each deal is scored separately, and a team making a part score gets an immediate bonus of 50 as in duplicate. The sequence of vulnerability is fixed as in the standard version.
A multiple of four hands can be played, repeating the sequence of vulnerabilities as often as necessary. The result is simply the total score over the deals played.
Chicago with Russian Scoring
The following method of scoring Chicago originated in Russia. It eliminates some of the luck of the deal by introducing an element of IMPs scoring.
On each deal, there is a target score which depends on the number of high card points held. The cards are played in front of the players, as in duplicate. At the end of the play, the high card points held by each side are counted, according to the following scale:
each ace: 4 points
each king: 3 points
each queen: 2 points
each jack: 1 point
There are 40 points in all. The team which held more high card points finds its target score, which depends on whether they were vulnerable or not, from the following table:
High Card Target
Points Not Vul. Vulnerable
20 0 0
21 50 50
22 70 70
23 110 110
24 200 290
25 300 440
26 350 520
27 400 600
28 430 630
29 460 660
30 490 690
31 600 900
32 700 1050
33 900 1350
34 1000 1500
35 1100 1650
36 1200 1800
37 1300 1950
38 1300 1950
39 1300 1950
40 1300 1950
The difference between the target score from the above table and the actual score is then converted to IMPs, using the standard IMP table. The total IMP scores over a series of hands are totaled to give an overall result.
For example, suppose we are East-West, and on the second deal of a Chicago we bid three hearts and make 10 tricks. We then count our high card points and discover that between us we had 24. We were vulnerable, so our target score from the table was 290. We actually scored 170 (90 for the contract plus 30 for the overtrick plus 50 for the part score). So we are 120 points short of our target. Therefore using the IMP table, our score for this hand is minus 3 IMPs.