Rule of 10-12

In bridge, the Rule of 10-12 is applied when the opening lead is the third or the fifth best from the defender's suit. By subtracting the rank of the card led from 10 or 12, a defender can figure out how many cards are higher than the card partner has led. 10 is used if the lead is fifth best ^[1] and 12 is used if lead is the third best.^[2] Rule of 11 applies when lead is the 4th best.

When following the Rule of 10-12 lead is the third card from 3 or 4 card suit and the fifth card from 5+ cards suit. Leading the third best is also applied to interior sequences (K J 10 x x) which is less ambiguous than the top of interior sequence. The third best lead from interior sequence is called coded 9 & 10 leads.

Sometimes opening leader may choose to lead the fourth best card from 4 card suit against no trump contract if third card is a spot card. The spot card lead may give declarer a trick that she can't get if the fourth best is led.

	Q 6 5 4
K 9 73	W    N↑ S↓    E	A 10 2
	J 8

If opening lead is 7 suit will be blocked and defense is unable to set up the 3rd winner in the suit.

Variation

Possible variation that helps giving count from 5+ cards suit is leading the third best from even number of cards and the lowest from odd number.

See also

• Rule of 11
• Journalist Leads

References

1. ↑ Rule of 10
2. ↑ Rule of 12

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