Has a fit been reached?

For different purposes (such as deciding the nature of a double), it is often important to determine whether a fit has been reached.

As a general principle, a fit is deemed to have been reached when both sides know that partnership has 8+ cards in a suit, e.g.

• 1H > 2H
• 1D > (1S) > 2D 
• (Even incomplete) minor transfer after 1NT, e.g. 1NT > 2NT > (3D)

The following lists the exceptions to the above rule. In the following situations, a fit is defined to have been reached even though the 8-card fit has not been explicitly guaranteed:

• 1C > 2C
• 1C > (1A) > 2C
• 2M > (below 3M) > X
• 2M > (X) > XX
• Unusual jump, e.g. 1H > 2S > 2H > 4D

In the following situations, a fit has not been reached:

• A response to partner's takeout double, e.g. (1D) > X > 1S
• Major transfer after 1NT