Mental Multiplication Tricks

Why learn mental tricks?

Reaching for a calculator for every sum slows you down. With a handful of clever mental multiplication tricks, you can work out answers in your head faster than you could type them. Each trick turns one hard multiplication into a couple of easy steps you already know from your times tables.

Trick 1: Multiplying by 10, 100 and 1000

This is the foundation for many other tricks. To multiply a whole number by 10, the digits shift one place to the left and a zero fills the gap:

36 × 10 = 360    36 × 100 = 3,600

There is a full lesson on this in multiplying by 10, 100 and 1000.

Trick 2: Double for ×4 and ×8

Multiplying by 4 is the same as doubling twice. Multiplying by 8 is doubling three times.

Example — 7 × 8.

1. Double 7: 14.
2. Double again: 28.
3. Double once more: 56.

So 7 × 8 = 56. Why? Because 2 × 2 × 2 = 8, so three doubles make eight lots.

Trick 3: ×5 means ×10 then halve

Five is half of ten, so to multiply by 5, multiply by 10 and then halve.

Example — 18 × 5.

1. 18 × 10 = 180.
2. Halve 180: 90.

So 18 × 5 = 90. The same idea gives ×50 (×100 then halve) and ×25 (×100 then quarter).

Trick 4: Near numbers

When a number is close to a round one — like 9, 19, 99 or 101 — multiply by the round number first, then adjust.

Example — 6 × 19.

1. 19 is close to 20, so do 6 × 20 = 120.
2. You added one extra lot of 6, so subtract it: 120 − 6 = 114.

So 6 × 19 = 114.

Sum	Round number step	Adjust	Answer
8 × 9	8 × 10 = 80	− 8	72
7 × 21	7 × 20 = 140	+ 7	147
5 × 99	5 × 100 = 500	− 5	495
4 × 101	4 × 100 = 400	+ 4	404

Trick 5: Split and add

For a two-digit number, split it into tens and ones, multiply each part, then add. This is the distributive law in action.

Example — 6 × 34.

1. Split 34 into 30 + 4.
2. 6 × 30 = 180.
3. 6 × 4 = 24.
4. Add: 180 + 24 = 204.

The times-9 finger trick

For the 9 times table (up to 9 × 10), hold up all ten fingers. To work out 9 × 4, bend down your 4th finger. The fingers to the left of the bent one are the tens (3) and the fingers to the right are the ones (6), giving 36. Try it for the whole nine times table.

A practice activity

Run a "speed round" with a partner:

1. One person calls out a multiplication; the other names which trick fits best.
2. Solve it aloud, explaining each step.
3. Time yourselves over ten questions, then swap.
4. Challenge: find a single calculation, like 16 × 25, that can be solved by two different tricks (e.g. doubling, or ×25 = ÷4 of ×100), and compare which is faster.

Where this leads

These tricks make long multiplication, percentages and everyday mental arithmetic far quicker. Practise them until they feel automatic, and combine them with mental math strategies for addition and subtraction to become a confident mental mathematician.