What is the Percentage Calculator?
The percentage calculator answers the three most common percent questions: what is X% of a number, what percent is one number of another, and how much has a value changed in percent.
How to use the Percentage tool
- Enter Number A, Number B and Calculation.
- The result updates instantly as you type, or press Calculate.
- Use Try an example to see how it works, and Reset to start again.
Formula
X% of Y = X ÷ 100 × Y. A is what % of B = A ÷ B × 100. Percentage change = (new − old) ÷ |old| × 100.
Worked example
With number a 15, number b 200, calculation What is A% of B?, the 15% of 200 is comes to 30.
Frequently asked questions
How do I calculate a percentage of a number?
Divide the percentage by 100 and multiply by the number. For example 15% of 200 is 0.15 × 200 = 30.
How do I turn a fraction into a percent?
Divide the top by the bottom and multiply by 100.
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Checked by Calcovate · Formula tested against worked examples · Updated 7 Nov 2026 · How we check our calculators.