Finding a percentage of a number is one of the most fundamental math operations in everyday life -- and there are several ways to do it depending on whether you have a calculator, prefer mental math, or want to understand the underlying formula. Here are three methods that always work.
Method 1: The Formula (Most Reliable)
The standard formula: Result = (Percentage / 100) x Number
This works for any percentage and any number, no exceptions.
- What is 35% of 240? (35 / 100) x 240 = 0.35 x 240 = 84
- What is 8% of 1,500? (8 / 100) x 1,500 = 0.08 x 1,500 = 120
- What is 12.5% of 80? (12.5 / 100) x 80 = 0.125 x 80 = 10
The key step is converting the percentage to a decimal by dividing by 100. Once you have the decimal, multiply by the number. This is what any calculator does internally.
Method 2: The Decimal Shortcut
For common percentages, you can skip the division step by memorizing the decimal equivalents:
| Percentage | Decimal | Quick way to think about it |
|---|---|---|
| 1% | 0.01 | Divide by 100 |
| 5% | 0.05 | Divide by 20 |
| 10% | 0.10 | Divide by 10 (move decimal left) |
| 20% | 0.20 | Divide by 5 |
| 25% | 0.25 | Divide by 4 |
| 50% | 0.50 | Divide by 2 |
| 75% | 0.75 | Multiply by 3, divide by 4 |
Example: What is 25% of 360? Divide 360 by 4 = 90. No calculator needed.
Method 3: Mental Math Using Building Blocks
For percentages that aren't in the table above, build them from 10% and 5%:
- 15% of 80: 10% of 80 = 8. 5% of 80 = 4. Total: 8 + 4 = 12.
- 30% of 150: 10% of 150 = 15. Multiply by 3: 15 x 3 = 45.
- 35% of 200: 30% = 60. 5% = 10. Total: 60 + 10 = 70.
- 45% of 80: 50% = 40. Subtract 5%: 40 - 4 = 36.
The building block method is slower than a calculator but fast enough for quick estimates when you don't have one handy.
Common Mistakes to Avoid
- Forgetting to divide by 100: 35% of 200 is not 35 x 200 = 7,000. It's 0.35 x 200 = 70.
- Confusing "percent of" with "percent off": 20% of $80 is $16. 20% off $80 means you pay $64.
- Rounding too early: If you round mid-calculation, small errors compound. Round only the final answer.
For any calculation beyond simple mental math, our Percentage Calculator handles any combination instantly -- just enter the percentage and the number.