Quick mental maths shortcuts for children and adults

The most useful mental maths tricks turn one hard calculation into two easy ones, so 68 × 9 becomes 680 − 68 and 350 ÷ 5 becomes 700 ÷ 10.

None of them is magic. Each one leans on place value and on facts your child already knows, which is exactly what the national curriculum asks of primary pupils, and what the Year 6 arithmetic paper rewards: 30 minutes, no calculator, one answer per box. Most of the examples below come from that 2026 paper, so you can see where each shortcut saves time.

Rounding and adjusting: the trick behind most of the others

Round one number to something easy, do the sum, then correct what you added or took away. For 87 + 327, add 90 instead of 87, which gives 417, then take back the 3 you added too many: 414. For 4,381 − 2,289, subtract 2,300 to get 2,081, then add back the 11 you took away too many: 2,092.

The same move checks answers. The national curriculum for England asks Year 5 pupils to use rounding to check answers and to judge the level of accuracy a problem needs, and Year 6 pupils to perform mental calculations, including with mixed operations and large numbers. If 4,381 − 2,289 is about 4,400 − 2,300, the answer must be close to 2,100: a written answer of 2,902 is wrong before you even redo it.

Adding in your head, left to right

On paper, column addition starts with the units. In your head, it is easier to start with the biggest part, because that is the part you remember. For 5,555 + 555 + 55: 5,555 + 500 is 6,055, plus 55 is 6,110, plus 55 is 6,165.

The curriculum builds this step by step: in Year 2, adding a two-digit number and ones or tens mentally; in Year 3, a three-digit number and ones, tens or hundreds; in Year 5, numbers that keep getting larger. Decimals work the same way. For 48.5 + 7.392, add the whole numbers first, 48.5 + 7 = 55.5, then the rest, 55.5 + 0.392 = 55.892.

Near doubles are another quick win. 48 + 49 is double 48 plus 1, so 97; 125 + 127 is double 125 plus 2, so 252. Children who know their doubles by heart get these almost for free.

Subtraction often goes faster by counting up. For 5,200 − 1,600, count from 1,600 to 2,000 (400) and from 2,000 to 5,200 (3,200): 3,600.

How to multiply by 5, 9 and 25 in your head

Most multiplication shortcuts swap an awkward number for 10, 100 or 1,000, which only move digits, and then fix the result with a halving or a subtraction. The table gathers the ones worth knowing; the examples marked with a star are questions from the 2026 KS2 arithmetic paper.

Partitioning handles the rest. The paper's 3 × 23 is 3 × 20 plus 3 × 3, so 60 + 9 = 69, and 99 ÷ 9 is 90 ÷ 9 plus 9 ÷ 9, so 10 + 1 = 11. Doubling twice multiplies by 4: 23 × 4 is 46, then 92.

The × 9 trick is the one that saves the most time, and it also explains the patterns of the 9 times table: 9 × 7 is 70 − 7, so 63.

The times 11 trick, and why it works

For a two-digit number times 11, write the two digits apart and put their sum in the middle. 11 × 34: 3, then 3 + 4 = 7, then 4, so 374. 11 × 52: 5, 7, 2, so 572.

When the digits add up to 10 or more, carry the 1 to the left. 11 × 78: 7 + 8 = 15, so write 5 in the middle and add 1 to the 7: 858.

It works because 11 × 34 is 340 + 34. The tens digit of 34 and its units digit both land in the middle column, which is why they add. Once children see that, the trick stops being magic and becomes a quick way of doing × 10 and adding the number, and it extends to the rest of the 11 times table beyond 11 × 9.

Percentages in your head, from 10% upwards

Find 10% by dividing by 10, then build the percentage you need. The 2026 arithmetic paper had three percentage questions, and each falls to the same method:

• 30% of 2,320: 10% is 232, three times that is 696.
• 97% of 400: the whole is 400, 1% is 4, so take away 3%: 400 − 12 = 388.
• 65% of 680: 50% is 340, 10% is 68, 5% is 34, so 340 + 68 + 34 = 442.

The trick is to choose the pieces that are easiest to find: 50% by halving, 10% by dividing by 10, 5% as half of 10%, 1% by dividing by 100. Our guide to percentages in your head goes further, with discounts and price rises.

Making mental maths shortcuts stick

Tricks help only when they come without thinking, and that takes short, regular practice. One shortcut a week is enough: use it every day in real situations, prices in a shop, minutes left before a train, a recipe for six instead of four, then add the next one.

Check every answer with a quick estimate or an inverse: the curriculum asks Year 4 pupils to estimate and use inverse operations to check answers. On the KS2 arithmetic paper, any method is accepted as long as the answer in the box is right; only long multiplication and long division questions are worth 2 marks, with 1 mark possible for a formal method. Kalc trains times tables, fractions, percentages and algebra in about ten minutes a day, which is the kind of regular practice that makes these shortcuts automatic.

Frequently asked questions

What is the easiest mental maths shortcut to learn first?

Rounding and adjusting: round one number to a ten or a hundred, do the easy sum, then correct. 87 + 327 is 327 + 90 − 3 = 414.

How do you multiply by 9 in your head?

Multiply by 10, then subtract the number once: 68 × 9 = 680 − 68 = 612.

How does the times 11 trick work?

For a two-digit number, write its digits apart and put their sum in the middle: 11 × 34 = 374. It works because 11 × 34 is 340 + 34.

How do you find a percentage of a number mentally?

Start from 10% by dividing by 10, then combine: 65% of 680 is 50% (340) + 10% (68) + 5% (34) = 442.

Can children use these shortcuts in the KS2 arithmetic paper?

Yes. The paper takes 30 minutes without a calculator and marks the answer in the box; only long multiplication and long division questions also give a mark for a formal method.