Mental math tricks for kids that actually make sense.
Mental math for kids means working out answers in your head by using what you already know about numbers, such as tens, doubles and halves. The tricks below are easy to learn, and each one comes with the reason it works, so children can use it with confidence instead of treating it as magic.
1. Make a ten when adding
For 8 + 5, take 2 from the 5 to turn 8 into 10. Then 10 + 3 = 13. Tens are the easiest numbers to add to.
8 + 5 = 8 + 2 + 3 = 13
2. Add 9 by adding 10
Adding 10 is easy, and 9 is one less. So 34 + 9 is 34 + 10 = 44, minus 1 = 43.
34 + 9 = 44 − 1 = 43
3. Near doubles
Children usually know their doubles first. Use them: 6 + 7 is double 6 plus one more.
6 + 7 = 6 + 6 + 1 = 13
4. Subtract by counting up
For 52 − 47, count up from 47 instead: 3 more makes 50, then 2 more makes 52. That is 5 altogether.
52 − 47 = 3 + 2 = 5
5. Multiply by 10
Every digit moves one place to the left, so 23 becomes 230. Say it this way rather than “add a zero”, because that rule breaks with decimals later.
23 × 10 = 230
6. Multiply by 5: half of ten
Multiply by 10, then halve. For 5 × 14: 14 × 10 = 140, and half of 140 is 70.
5 × 14 = 140 ÷ 2 = 70
7. Multiply by 4: double, then double again
For 4 × 13, double 13 to get 26, then double 26 to get 52.
4 × 13 = 26 × 2 = 52
8. The 9 times table finger trick
Hold up ten fingers. For 9 × 3, fold down the third finger from the left. There are 2 fingers left of it and 7 to the right: 27. It works from 9 × 1 to 9 × 10.
9 × 3 = 27
9. Multiply by 11
Keep the outside digits and add the middle: 43 × 11 = 4, then 4 + 3, then 3, which is 473.
43 × 11 = 473
See the full multiply by 11 trick, including carries and 3-digit numbers.
A math magic trick for kids
Ask your child to think of any number. Double it. Add 10. Halve the result. Now take away the number they first thought of. Announce: “Your answer is 5!” It always is.
Once they are amazed, show them why: doubling and then halving cancel out, so they are left with their number plus 5. Taking the original number away leaves exactly 5. Change the “add 10” to “add 20” and the answer becomes 10, so they can invent their own version.
How to practise mental math with kids
Pick one trick a week and use it in everyday moments: prices in a shop, scores in a game, the time left before dinner. A few questions in the car are worth more than a long worksheet. When a trick feels easy, ask your child to explain it to you; teaching it back is the best sign they understand it.
For more structured practice, try our multiplication games for kids, the step-by-step guide to teaching multiplication or the Trachtenberg Kids app, which turns tricks like these into guided lessons.