Mental Math Tricks for Kids and Students

1. Round, then adjust

To add 47 + 28, round 28 up to 30: 47 + 30 = 77. You added 2 too many, so take 2 off: 75.

The same idea works for subtraction: 63 − 29 is 63 − 30 + 1 = 34.

2. Break numbers apart

7 × 14 is hard in one step. Split 14 into 10 and 4: 7 × 10 = 70 and 7 × 4 = 28. Add them: 98.

3. Make a ten

For 8 + 7, take 2 from the 7 to make 8 + 2 = 10, then add the remaining 5: 15.

4. Halve and double

25 × 16: halve 16 to 8 and double 25 to 50. Then 50 × 8 = 400. Or think of 25 as a quarter of 100: 16 quarters of 100 is 4 × 100 = 400.

5. Percentages from 10%

To find 15% of 80, find 10% (8), then 5% which is half of that (4). Add: 12.

Our percentage calculator can check your answer.

6. Squaring numbers that end in 5

For 35², multiply the tens digit by the next number up: 3 × 4 = 12. Then write 25 after it: 1225.

7. Use friendly numbers for division

To divide 84 by 4, halve twice: 84 → 42 → 21.

8. Estimate first

Before a hard calculation, estimate: 49 × 21 is about 50 × 20 = 1000. If your exact answer is far from 1000, check it. (The exact answer is 1029.)