Percentage Calculator
Calculate X% of Y, find what percent one number is of another, and work out percentage increase or decrease — all instantly, right in your browser.
🔒 Processed locally in your browser
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How to use
- Pick a calculation type at the top: "X% of Y", "X is what % of Y", or "% change from X to Y".
- Enter your two numbers into the X and Y fields — the labels update to match the calculation you picked.
- The result updates live below as soon as you type — there's no button to press.
- Use Reset to restore the example numbers for the current calculation type.
Features
- Three calculation modes in one tool: percent of a number, what-percent-is, and percentage change
- Live results as you type — no button to press
- Clear +/− sign on percentage increase and decrease results
- Inline validation catches invalid numbers and divide-by-zero cases before they show as NaN or Infinity
- 100% client-side — your numbers never leave your browser
Frequently asked questions
How do I calculate X% of Y?
Switch to the "X% of Y" mode, enter your percentage in the X field and the number in the Y field. For example, 20% of 150 is 30.
How do I find what percent one number is of another?
Switch to the "X is what % of Y" mode. Enter the part in X and the whole in Y — for example, 30 is 20% of 150.
How do you calculate percentage increase or decrease?
Switch to the "% change from X to Y" mode, enter the starting value in X ("From") and the ending value in Y ("To"). A positive result means an increase, a negative result means a decrease — for example, going from 120 to 100 is a change of about -16.67%.
Why does it say a value can't be zero?
Dividing by zero is mathematically undefined. This happens if Y is 0 in "X is what % of Y" mode, or if the "From" value is 0 in "% change" mode — enter a non-zero number to see a result.
Does this tool send my numbers anywhere?
No. Percentage Calculator runs entirely in your browser — all the math happens locally and nothing is ever sent to a server.