How to Multiply by 25 in Your Head

Level 2 Mental multiplication · Reviewed by The NumThink editorial team · Last reviewed

Short version: To multiply by 25, multiply by 100 and divide by 4. 84 × 25 = 8,400 ÷ 4 = 2,100.

25 is a quarter of 100 — so multiplying by it is two halvings away from a free ×100. It also quietly teaches quarters, a quarter of the percentage tricks you'll ever need.

Try it now

No signup · instant feedback

Why it works

25 is a quarter of 100, so n × 25 = n × 100 ÷ 4. Multiplying by 100 is free (append two zeros), and quartering is just halving twice — two very reliable mental steps.

This also explains why so many ×25 answers "look round": a quarter of a multiple of 100 always ends in 00, 25, 50, or 75.

The steps

  1. Multiply by 100. Append two zeros: 84 → 8,400.
  2. Halve once. 8,400 ÷ 2 = 4,200.
  3. Halve again. 4,200 ÷ 2 = 2,100. Done.

Worked examples

easy 48 × 25

Show the thinking

48 × 100 = 4,800

4,800 ÷ 4 = 1,200

So 48 × 25 = 1,200.

Answer: 1,200

medium 84 × 25

Show the thinking

84 × 100 = 8,400

8,400 ÷ 2 = 4,200, ÷ 2 again = 2,100

So 84 × 25 = 2,100.

Answer: 2,100

hard 132 × 25

Show the thinking

132 × 100 = 13,200

13,200 ÷ 4 = 3,300

So 132 × 25 = 3,300.

Answer: 3,300

When to use it

  • Any multiplication by 25 — it turns into halving twice.
  • Percentages: 25% of a number is the same ×25 pattern divided by 100 (25% of 84 = 21).

When not to use it

  • When the other factor is already a multiple of 4 — direct multiplication may be as fast (8 × 25 = 200 from memory).
  • Numbers ending in awkward quarters — 37 × 25 still works (9,250 ÷ ... 3,700 ÷ 4 = 925), but watch the decimals: halve 3,700 = 1,850, halve again = 925. Slow down and be careful.

Common mistakes

Dividing by 4 before the zeros. Quartering the raw number and then appending zeros. Fix: It works out the same, but quartering 8,400 (halve twice) is easier than quartering 84 — do the big shift first.
Dropping a halve. Answering with ×50 instead of ×25. Fix: ×25 is TWO halvings after the ×100 step, not one.
Check yourself: Every ×25 answer ends in 00, 25, 50, or 75. Anything else means an arithmetic slip.