8 Percentage Tricks That Make Mental Math Easy

You don’t need a calculator for most everyday percentage problems. Here are 8 tricks that make percentage math fast enough to do in your head.

1. Move the decimal for 10%

Finding 10% of any number is just moving the decimal point one place left. 10% of 480 is 48.

2. Double it for 20%

Once you have 10%, doubling it gives you 20% instantly. 10% of 480 is 48, so 20% is 96.

3. Halve 10% for 5%

Cut your 10% figure in half to get 5%. If 10% of 480 is 48, then 5% is 24.

4. Build 15% from 10% + 5%

Add your 10% and 5% figures together. 48 + 24 = 72, so 15% of 480 is 72, useful for calculating tips fast.

5. Find 1% first for odd percentages

For percentages that don’t split cleanly (like 7% or 23%), find 1% first by moving the decimal two places, then multiply by the percentage you need.

6. 50% is always just half

The simplest one: 50% of any number is just that number divided by two.

7. Swap the order when it’s easier

X% of Y always equals Y% of X. 8% of 50 is awkward, but 50% of 8 (which is just 4) is instant, and gives you the same answer.

8. Round first, adjust after

For a quick estimate, round the number to something easier, calculate the percentage, then adjust slightly. 18% of 97 is close enough to 18% of 100 (which is 18) minus a small adjustment.

For anything that needs to be exact, not just close, our percentage calculator handles it instantly, and our tip calculation guide walks through the restaurant-specific version of these tricks.