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How this calculator works
Percent means per hundred. Choose the question you are asking: what is X% of Y, X is what percent of Y, or the percent change from X to Y. Percent change divides the difference by the starting value, so going from 50 to 75 is +50% but going back from 75 to 50 is −33.3%.
Formula
- X% of Y = X / 100 × Y
- X is what percent of Y = X / Y × 100
- Percent change from X to Y = (Y − X) / |X| × 100
Worked example
15% of 80
- Question
- What is X% of Y?
- X
- 15
- Y
- 80
Result12
15% of 80 is 12.
Frequently asked questions
How do I calculate a percentage of a number?
Divide the percentage by 100 and multiply by the number. 15% of 80 is 0.15 × 80 = 12.
How do I calculate percent increase?
Subtract the old value from the new one, divide by the old value and multiply by 100. From 40 to 50 is (50 − 40) / 40 × 100 = 25%.
What is the difference between percent and percentage points?
A rate rising from 4% to 5% went up by 1 percentage point, which is a 25% increase. Percentage points measure the absolute gap; percent measures the relative change.
Sources
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Results are estimates based on the values you enter and the published method shown above. They do not replace professional medical, financial or legal advice. Method reviewed October 7, 2026. About this site