How to Multiply by 11 in Your Head

Updated 12 October 2026

Split the digits and tuck their sum in the middle.

43 × 11 = 473

How do you multiply by 11 in your head?

To multiply a two-digit number by 11, write its two digits with their sum between them. For 43 × 11, the first digit is 4, the middle is 4 + 3 = 7, and the last digit is 3, giving 473. It works because 11 is 10 + 1, so 43 × 11 = 430 + 43, and adding those two lines puts the 4 in the hundreds, the 3 in the units, and 4 + 3 in the tens. When the digits add to 10 or more, the sum is too big for one place, so write its units digit in the middle and carry the 1 into the hundreds: 86 × 11 has 8 + 6 = 14, so write 4 and raise the 8 to 9, giving 946. A three-digit number works the same way with two middle sums: 123 × 11 is 1, then 1 + 2 = 3, then 2 + 3 = 5, then 3, so 1353.

1. 43 × 11 the long way is two rows: one 43, and ten of them shifted up.

2. Adding them, the tens column holds 4 + 3 — the digit sum lands in the middle.

3. Split the digits, tuck the sum between. Sum 10 or more? Carry the 1.

What if the digits add to 10 or more?

The sum still goes in the middle, but it has two digits now, so the 1 carries into the hundreds. For 75 × 11, 7 + 5 = 12: write the 2 in the middle and add the 1 to the 7, which gives 825. Check it the long way: 750 + 75 = 825.

How do you multiply a three-digit number by 11?

Keep the first and last digits and put the sum of each neighboring pair between them. For 234 × 11 the first digit is 2, then 2 + 3 = 5, then 3 + 4 = 7, then the last digit 4, so 2574. It is the same addition as before: 2340 + 234 lines each digit up beside its neighbor.

Work from the right so the carries land. For 687 × 11 the last digit 7 stays; 8 + 7 = 15, so write 5 and carry 1; 6 + 8 + 1 = 15, so write 5 and carry 1; and the leading 6 takes that carry to make 7. Read it off: 7557. Check: 6870 + 687 = 7557.

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