Mental Math Tricks Everyone Should Know
Calculate Faster in Your Head — No Calculator Needed
Mental math is the ability to calculate in your head without paper or a calculator. It's a super useful skill that saves time, builds number sense, and makes you faster at everything from shopping to school tests. The best part? Anyone can get better with a few simple tricks. Here are some of the most useful ones.
1. Round and Adjust
When adding numbers close to round numbers, round one up and then fix it. For example, 47 + 39: add 47 + 40 = 87, then subtract the 1 you added, giving 86. This trick makes messy numbers much easier to add quickly.
2. Break Numbers Apart (Splitting)
Break big numbers into parts. For 56 + 28, split into 50 + 20 = 70 and 6 + 8 = 14, then add them: 70 + 14 = 84. Splitting turns scary math into a few simple steps you can do in seconds.
3. Use Doubles and Near-Doubles
If you know your doubles (6 + 6 = 12), you can solve near-doubles instantly. 7 + 6 is double 6 plus 1, so 12 + 1 = 13. This trick works great for young learners mastering addition.
4. Multiply by 10, 100, or 1,000
To multiply any number by 10, just add a zero. Multiply by 100, add two zeros. This sounds obvious, but it's the foundation for mental multiplication with larger numbers. For example, 47 × 100 = 4,700.
5. The 9s Trick (Fingers Up)
Multiplying by 9 has a neat pattern. For 9 × n, hold up ten fingers and fold down the nth finger. The digits to the left and right give the answer. For 9 × 4, folding the 4th finger shows 3 fingers left and 6 right, so 36. It works for all single-digit multipliers.
6. Squaring Numbers Ending in 5
To square a two-digit number ending in 5, multiply the tens digit by one more than itself, then put 25 at the end. For 35²: 3 × 4 = 12, then add 25 → 1225. For 85²: 8 × 9 = 72 → 7225. It works every time!
7. Multiply by 11 (Two Digits)
To multiply a two-digit number by 11, add the digits and place the sum in the middle. For 34 × 11: 3 + 4 = 7, so the answer is 374. If the sum is 10 or more, carry the 1: 57 × 11 → 5 + 7 = 12, so 627.
8. Percentage Shortcuts
10% of any number is just moving the decimal one place left. So 10% of 250 is 25. Once you know 10%, you can find 5% (half of 10%), 20% (double 10%), and more. Discounts and tips become easy to compute.
9. Practice Makes It Automatic
Like any skill, mental math improves with practice. Start with small numbers and work up. Try doing grocery totals in your head, or time yourself on a few problems each day. The goal is to make these tricks feel automatic.
Ready to sharpen your skills? Our math apps generate unlimited practice problems that are perfect for building your mental math speed. Unsure about a trick? Ask in Math Q&A.