Percentage calculator
The four percentage questions people ask most, answered as you type.
Percentage of a number
What percent
Percentage change
Add or subtract a percentage
Formulas
How percentages work
"Percent" means "per hundred", so 20% is 20 out of every 100, or 0.2 as a decimal. Every percentage calculation comes down to one of these formulas:
| Question | Formula | Example |
|---|---|---|
| What is X% of Y? | Y × X ÷ 100 | 20% of 150 = 30 |
| X is what % of Y? | X ÷ Y × 100 | 30 of 150 = 20% |
| Change from X to Y | (Y − X) ÷ X × 100 | 80 → 100 = +25% |
| Y plus X% | Y × (1 + X ÷ 100) | 200 + 15% = 230 |
| Y minus X% | Y × (1 − X ÷ 100) | 200 − 15% = 170 |
A handy trick for mental math
Percentages are reversible: X% of Y is the same as Y% of X. So 8% of 50 is the same as 50% of 8, which is 4. When one way round is hard, try the other.
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Frequently asked questions
How do I calculate a percentage of a number?
Multiply the number by the percentage and divide by 100. For example, 20% of 150 is 150 × 20 ÷ 100 = 30. On a calculator you can also multiply by the decimal: 150 × 0.2 = 30.
How do I work out what percentage one number is of another?
Divide the part by the whole and multiply by 100. For example, 30 out of 150 is 30 ÷ 150 × 100 = 20%.
How do I calculate a percentage increase or decrease?
Subtract the old value from the new one, divide by the old value and multiply by 100. From 80 to 100 is (100 − 80) ÷ 80 × 100 = 25% increase. A negative result is a decrease.
Why doesn't adding 10% and then removing 10% give the original number?
Because the second percentage is taken of a different number. 100 plus 10% is 110, but 10% of 110 is 11, so removing it leaves 99. To undo a 10% increase, divide by 1.10 instead.
What is the difference between percent and percentage points?
Percentage points measure the gap between two percentages; percent measures relative change. An interest rate going from 2% to 3% rose by 1 percentage point, which is a 50% increase.