The Rule of 15 is not a mathematical calculation, but rather a general rule of thumb. Not everything about the game of bridge falls within the realm of calculations and mathematics. Sometimes you just have to apply logic and reasoning based upon certain information and practiced guidelines.

Concept of the Rule

Simply stated, the Rule of 15 allows the bridge player, following three consecutive passes, in the fourth seat to better determine whether or not to open the auction by bidding.

The Rule of 15 states that the player in the fourth seat should open the auction, if the number of high card points added to the number of Spades equals 15 or more.

These points are also known as Pearson Points and also as Cassino Points. The logic and reasoning behind the Rule of 15 considers the proposition that the high card points are very likely evenly divided between the two partnerships. Therefore, following three consecutive passes the fourth seat should open only with a Spade suit, thereby declaring that he does have the boss suit. Possessing the Spade suit almost assures the partnership against intervention from the opponents.

The Rule of 15 can be used effectively, but should be adhered to. If fourth seat counts fewer than 15 points, after adding the high card points and the number of Spades, then fourth seat should pass.

Additional Details

There is also another feature of the Rule of 15, which is a mathematical calculation and/or device employed to assist the player to remember how many higher cards are outstanding in a suit whether the partnership agreement's leads are third, fourth, or fifth best of his/her long suit.

The player simply subtracts the pip or rank of the card led from the number 15 and uses that rule or mathematical calculation. If the card led is fifth best, then subtract five from fifteen and use the Rule of Ten. If the card led is fourth best, then substract four from fifteen and use the Rule of Eleven. If the card led is third best, then subtract three from fifteen and use the Rule of Twelve.

Note: Although the Rule of 15 was originally designed, devised, and developed for the player in the fourth seat following three consecutive passes, there is no mandatory or obligatory regulation by any authoritative body that the player in the third seat, second seat, or even the first seat may not make use of this concept.

If you wish to include this feature, or any other feature, of the game of bridge in your partnership agreement, then please make certain that the concept is understood by both partners. Be aware whether or not the feature is alertable or not and whether an announcement should or must be made. Check with the governing body and/or the bridge district and/or the bridge unit prior to the game to establish the guidelines applied. Please include the particular feature on your convention card in order that your opponents are also aware of this feature during the bidding process, since this information must be made known to them according to the Laws of Duplicate Contract Bridge. We do not always include the procedure regarding Alerts and/or Announcements, since these regulations are changed and revised during time by the governing body. It is our intention only to present the information as concisely and as accurately as possible.