How to Multiply by 101 in Your Head

Updated 4 October 2026

Just repeat the number — no mental math.

43 × 101 = 4343

How do you multiply a two-digit number by 101?

To multiply a two-digit number by 101, write it twice: 43 × 101 = 4343. It works because 101 is 100 + 1, so 43 × 101 = 4300 + 43. The 4300 leaves two empty places at the end, and the 43 drops straight into them, so the number appears twice with nothing to carry. The trick needs the number to have exactly two digits. A single digit sits with a 0 in front of its copy: 7 × 101 = 707. A three-digit number overlaps with its copy, so add the two lines instead: 256 × 101 = 25600 + 256 = 25856. Multiplying by 1001 does for three-digit numbers what 101 does for two-digit ones, because 1001 is 1000 + 1: 256 × 1001 = 256256. And 10101 repeats a two-digit number three times: 43 × 10101 = 434343. Check by dividing back: 4343 ÷ 43 = 101.

1. 101 is 100 + 1: a hundred 43s, then one more 43.

2. The 43 drops into the two places the zeros left empty: 4343.

3. So the shortcut: write the number twice. Any 2-digit number works.

All 36 shortcuts: the Magic Tricks library.