How to Multiply by 5 in Your Head

Level 1 Mental multiplication · Reviewed by The NumThink editorial team · Last reviewed

Short version: To multiply by 5, multiply by 10 and then halve. 86 × 5 = 860 ÷ 2 = 430.

Multiplying by 5 is the friendliest of the mental math families: one free step (×10) and one practiced step (halving). If you learn a single trick on this site, make it this one.

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Why it works

5 is exactly half of 10. Because multiplication scales, you can take the big easy step first (×10) and then split the result in two (÷2): n × 5 = n × 10 ÷ 2.

Multiplying by 10 is free — just append a zero. Halving a number is one of the most practiced mental operations, so the whole calculation collapses into something you can hold in your head.

The steps

  1. Multiply by 10. Append a zero to the number: 86 becomes 860.
  2. Halve the result. 860 ÷ 2 = 430. That is the answer to 86 × 5.

Worked examples

easy 8 × 5

Show the thinking

8 × 10 = 80

80 ÷ 2 = 40

So 8 × 5 = 40.

Answer: 40

medium 86 × 5

Show the thinking

86 × 10 = 860

860 ÷ 2 = 430

So 86 × 5 = 430.

Answer: 430

hard 1,246 × 5

Show the thinking

1,246 × 10 = 12,460

12,460 ÷ 2 = 6,230

So 1,246 × 5 = 6,230.

Answer: 6,230

When to use it

  • Any multiplication by 5, no matter how large the number.
  • Multiplying by 50: multiply by 100 instead of 10, then halve (64 × 50 = 6,400 ÷ 2 = 3,200).
  • Odd numbers too: 87 × 5 = 870 ÷ 2 = 435.

When not to use it

  • Single-digit facts you already know by heart (6 × 5) — direct recall is faster.
  • Multiplications by numbers near 5, like ×6 or ×4 — use doubling instead: ×6 = ×5 + the number, or just halve ×12.

Common mistakes

Forgetting the halve. Answering with ten times too much. Fix: Always finish with the halving step — the answer must be 5 times the number, not 10.
Halving the wrong number. Halving the original number before multiplying by 10. Fix: That also works (43 × 10 = 430), but halving 860 is usually easier than halving 86 — pick whichever is smoother for you.
Check yourself: Every answer to ×5 must end in 0 or 5. If yours does not, you dropped the halving step.