Percentage calculator
Three quick percentage calculators in one place. Just fill in the boxes and the answer updates as you type.
Percentage formulas
| Question | Formula | Example |
|---|---|---|
| X% of Y | X ÷ 100 × Y | 15% of 80 = 12 |
| X as a % of Y | X ÷ Y × 100 | 30 of 120 = 25% |
| % change | (new − old) ÷ old × 100 | 200 → 250 = +25% |
| Add X% to Y | Y × (1 + X ÷ 100) | 80 + 15% = 92 |
| Take X% off Y | Y × (1 − X ÷ 100) | 80 − 15% = 68 |
Handy shortcuts
- 10%: move the decimal point one place left (10% of 340 is 34).
- 5%: half of 10% (5% of 340 is 17).
- 1%: move the decimal point two places left (1% of 340 is 3.4).
- Percentages are reversible: 8% of 50 is the same as 50% of 8, which is 4.
Need to work with VAT specifically? Use our VAT calculator.
Frequently asked questions
How do I work out a percentage of a number?
Divide the percentage by 100 and multiply by the number. For example, 15% of £80 is 0.15 × 80 = £12.
How do I work out what percentage one number is of another?
Divide the first number by the second and multiply by 100. For example, 30 out of 120 is 30 ÷ 120 × 100 = 25%.
How do I calculate percentage increase?
Subtract the old value from the new value, divide by the old value and multiply by 100. For example, going from £200 to £250 is (250 − 200) ÷ 200 × 100 = a 25% increase.
How do I calculate a percentage decrease?
Use the same formula as for an increase. The result will be negative. Going from £250 to £200 is (200 − 250) ÷ 250 × 100 = −20%, a 20% decrease.
Why isn't a 20% rise followed by a 20% fall back to the start?
Because the second percentage is taken from a bigger number. £100 up 20% is £120, and £120 down 20% is £96.
Last checked 5 October 2026.