The formula
X% of Y = Y × X ÷ 100
Or convert the percent to a decimal first (20% → 0.20) and multiply: 0.20 × 150 = 30.
Examples
- 20% of 150 = 150 × 20 ÷ 100 = 30
- 7.5% of 240 = 240 × 7.5 ÷ 100 = 18
- 15% of $64 = 64 × 0.15 = $9.60
- 120% of 50 = 50 × 1.2 = 60 (over 100% means more than the original)
Mental math shortcuts
- 10% — move the decimal one place left: 10% of 86 = 8.6
- 5% — half of 10%: 5% of 86 = 4.3
- 15% — 10% + 5%: 8.6 + 4.3 = 12.9
- 20% — double 10%: 17.2
- 25% — divide by 4: 21.5
- 1% — move the decimal two places: 0.86, then multiply for any whole percent
The swap trick
X% of Y always equals Y% of X. So 8% of 50 is the same as 50% of 8 = 4. Pick whichever is easier.
Quick reference table
| Percent | of 40 | of 60 | of 80 | of 120 | of 250 |
|---|---|---|---|---|---|
| 5% | 2 | 3 | 4 | 6 | 12.5 |
| 10% | 4 | 6 | 8 | 12 | 25 |
| 15% | 6 | 9 | 12 | 18 | 37.5 |
| 20% | 8 | 12 | 16 | 24 | 50 |
| 25% | 10 | 15 | 20 | 30 | 62.5 |
| 30% | 12 | 18 | 24 | 36 | 75 |
| 50% | 20 | 30 | 40 | 60 | 125 |
| 75% | 30 | 45 | 60 | 90 | 187.5 |
FAQ
What is 20% of 80?
80 × 20 ÷ 100 = 16.
What is 15% of 200?
200 × 0.15 = 30.
How do I find a percentage on a calculator?
Type the number, multiply by the percent, then divide by 100 (or multiply by the decimal form). For 30% of 70: 70 × 30 ÷ 100 = 21.
How do I add a percentage to a number?
Multiply by (1 + percent as a decimal). Adding 8% to $50: 50 × 1.08 = $54.
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