If you are learning to play bridge, sooner or later you will come across the Rule of 11. But what is it and how should you use it?
What is the Rule of 11?
It is usually used in a no trump contract, by the third player in a game of bridge. If you are the third player, you use it if you think that your partner led with the 4th highest card in their longest suit.
After your partner has played, you can see the cards in dummy's hand and you also know the cards in your own hand. The Rule of 11 will let you work out if the remaining player has any cards that are higher than the card led by your partner. If they don't and dummy played low, then you don't need to play a higher card than your partner in order to win the trick. It helps you win the trick as cheaply as possible.
How to Use the Rule of 11
Here is an example. Your partner has played the 7. Dummy played 2 and you can see that dummy also holds Q and 8. You hold A, 10 and 3. Should you play a higher card than your partner to win the trick?
You think your partner played their 4th highest card so you can use this rule to work out which card to play. Deduct 7 (the card played by your partner) from 11. This gives you 4 - which tells you that there are four cards higher than 7 NOT held by your partner. You hold A and 10 and dummy holds Q and 8 - so you can see all of those four cards. This tells you that the declarer doesn't hold any card higher than 7, so you can play your 3 and your partnership will still win the trick.