Percentage calculator
Six common percentage questions in one place: what is X% of Y, X is what % of Y, percentage change, and adding or taking off a percentage.
Of
What is % of ?
What percent
is what % of ?
Change
From to
Add or take off
Take and %
X% of Y is X ÷ 100 × Y. 15% of 240 is 0.15 × 240 = 36. To find what percent A is of B, divide A by B and multiply by 100. Percentage change is (new − old) ÷ old × 100, so going from 80 to 100 is a 25% increase, but going back from 100 to 80 is a 20% decrease. The base is different each time.
To add a percentage, multiply by 1 plus the percentage as a decimal. For example +20% is × 1.2. To take one off, multiply by 1 minus it, so −20% is × 0.8. Taking 20% off and then adding 20% back doesn't get you to where you started.
How do I work out 10% of a number?
Move the decimal point one place left. 10% of 85 is 8.5.
How do I calculate a percentage increase?
Subtract the old number from the new one, divide by the old number and multiply by 100. The 'Change' box does it.
Why isn't a 20% rise followed by a 20% fall back to the start?
The second change is 20% of a bigger number, so it takes off more than the first added.
How do I work out a discount?
Use 'Add or take off' with subtract. £200 with 20% off is £160.
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Free to use. Results are for convenience: check anything important before you rely on it.