The Rule of 18 is a rule employed by the World Bridge Federation to define the boundary between light opening bids and Highly Unusual Methods, known as HUM, in which bad hands are regularly opened. There is a mathematical calculation involved.
Parameters of the Rule
1. Only if the number of high card points added to the total of the two longest suits totals 18, then the bid is accepted by the World Bridge Federation.
2. In the bridge community of England, the Rule of 19 is the appropriate guideline for determining whether to open the auction.
The player who decides to open a hand containing only 10 high card points bases this decision to open on the length of his suit-distribution of the holding. For example, if the player’s distribution is 3-2-4-4 and the player counts 10 high card points, then these 10 points are added to the 4-4 distribution (the two longest suits), and the total number equals 18, then an opening bid becomes acceptable at any bridge tournament conducted by the World Bridge Federation.
Note: Some sponsoring organizations may include the provision that the holding, which meets the above criteria, must also include two quick tricks, or two playing tricks.
If the distribution of the player is 5-5-2-1 and the player has only 8 high card points, then the player calculates 10 points for the two longest suits (5+5), adds the 8 high card points for a total count, which equals 18. The player is allowed by the World Bridge Federation to open the bidding with a holding of only eight high card points.
Note: if the distribution 5-5-2-1, which equals 10 points for the two longest suits, and the holding contains only 7 high card points, then the result equals 17 points. The player would be disallowed from opening the bidding when playing in tournaments sponsored by the World Bridge Federation.
As stated above, the Rule of 18 has been established to define the boundary between light opening bids and Highly Unusual Methods.