Guide
12 Mental Math Tricks Every Kid Should Know
These are shortcuts, not replacements for fact fluency — they work best once the basics are already reasonably solid, as a way to handle bigger numbers without paper.
Addition tricks
1. Add 9 by adding 10 and subtracting 1
27 + 9 is easier as 27 + 10 − 1 = 36. Works for any "add 9" problem, and extends to "add 8" (add 10, subtract 2).
2. Round and adjust
48 + 35 becomes 50 + 35 − 2 = 83. Rounding one number to a friendly value and correcting at the end is faster than adding awkward digits directly.
3. Add the tens, then the ones
36 + 27: add 30 + 20 = 50, then 6 + 7 = 13, then combine: 50 + 13 = 63. Splitting by place value is often faster than carrying in your head.
Subtraction tricks
4. Count up instead of down
For 82 − 76, counting up from 76 to 82 (just 6) is much faster than subtracting downward. This trick shines when the two numbers are close together.
5. Subtract 9 by subtracting 10 and adding 1
54 − 9 = 54 − 10 + 1 = 45. The mirror image of the addition trick above.
6. Use a friendly middle number
93 − 47: go from 47 up to 50 (+3), then 50 up to 93 (+43), then add the pieces: 3 + 43 = 46.
Multiplication tricks
7. Multiply by 5 using 10, then halve
18 × 5 = (18 × 10) ÷ 2 = 180 ÷ 2 = 90. Multiplying by 10 is instant, and halving is usually easier than multiplying by 5 directly.
8. Multiply by 4 or 8 by doubling repeatedly
13 × 4 = 13 doubled, doubled again: 26, then 52. For ×8, double a third time.
9. Break apart with the distributive property
7 × 23 = 7 × (20 + 3) = 140 + 21 = 161. Breaking a two-digit number into tens and ones makes most multiplication doable in your head.
10. Squaring numbers ending in 5
35² : take the leading digit (3), multiply by the next number up (4) to get 12, then append 25: answer 1225. Works for any two-digit number ending in 5.
All-purpose tricks
11. Check with estimation first
Before solving, round every number and estimate the ballpark answer. If the final answer is wildly off from the estimate, that's an instant red flag to recheck the work.
12. Say it, don't just think it
Talking through the steps out loud — even alone — catches errors that silent mental math tends to miss, especially for kids still building confidence.
Tricks are fastest to pick up once the underlying facts are already fluent — if a specific operation still feels shaky, a short session on the matching practice game is worth doing before layering shortcuts on top.