Calculators & everyday math
How to Calculate a Percentage of a Number
Finding a percentage of a number — 15% of a bill, 8% of a budget, 40% of a class — comes up constantly. There is one method that always works, and a handful of mental shortcuts that make the common cases quick. This guide covers both, with worked examples you can check.
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The method that always works
- Turn the percentage into a decimal by dividing it by 100: 15% becomes 0.15.
- Multiply the number by that decimal: 80 × 0.15 = 12.
- That’s it — 15% of 80 is 12. Multiplying first and dividing by 100 at the end (80 × 15 ÷ 100) gives the same answer.
Mental shortcuts
- 10%: move the decimal point one place to the left. 10% of 240 is 24.
- 5%: half of 10%. 5% of 240 is 12.
- 1%: move the decimal point two places to the left. 1% of 240 is 2.4.
- 25% is a quarter, 50% is a half, and 75% is three quarters: 25% of 240 is 60.
- Build other percentages from these. 15% is 10% plus 5%, so 15% of 240 is 24 + 12 = 36.
Swap the numbers when it’s easier
X% of Y always equals Y% of X, because both are X × Y ÷ 100. 8% of 50 looks awkward, but 50% of 8 is obviously 4 — and so is 8% of 50.
Worked examples
| Question | Working | Answer |
|---|---|---|
| 20% of 150 | 150 × 0.2 | 30 |
| 15% of 80 | 80 × 0.15 | 12 |
| 12.5% of 64 | 64 × 0.125 | 8 |
| 7% of 1,200 | 1,200 × 0.07 | 84 |
| 150% of 40 | 40 × 1.5 | 60 |
| 0.5% of 3,000 | 3,000 × 0.005 | 15 |
Percentage of a Number FAQ
- What is the formula for a percentage of a number?
- Number × percentage ÷ 100. For 15% of 80: 80 × 15 ÷ 100 = 12.
- How do I find 10% of a number quickly?
- Move the decimal point one place to the left: 10% of 356 is 35.6.
- How do I find 15% of a number in my head?
- Find 10%, halve it to get 5%, and add the two. For 60 that is 6 + 3 = 9.
- Can a percentage of a number be bigger than the number?
- Yes, whenever the percentage is over 100. 150% of 40 is 60.
- What are 0% and 100% of a number?
- 0% of any number is 0, and 100% of a number is the number itself.
Related guides
- Percentage FormulasThe three percentage questions — find the part, the rate, or the whole — and how to tell which one you are being asked, with the formula for each.
- Common Percentage MistakesWrong bases, percentages that don’t cancel, percentage points vs. percent, reversing a discount, and rounding too early — with a quick check for each.
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