Percentage Calculator
This free percentage calculator answers the three questions people actually ask about percentages, all in one place and all as you type.
How to use
- Pick the mode that matches your question: percent of a value, X as a percent of Y, or percent change.
- Enter the two numbers — the result appears immediately, no button needed.
- Read the formatted result: percent-of gives a plain number; the other two modes give a percentage.
- Change either number at any time and the answer updates instantly; everything stays on your device.
Frequently asked questions
How do I calculate X percent of a number?
Use the formula result = X / 100 × Y. Example: 25% of 200 = 25 / 100 × 200 = 50. The "What is X% of Y" mode does this for you.
How do I find what percent one number is of another?
Use the formula result = X / Y × 100. Example: 25 is what percent of 200? 25 / 200 × 100 = 12.5%. The denominator Y must not be zero — dividing by zero is undefined.
How is percentage change calculated?
The formula is result = (Y − X) / |X| × 100, where X is the starting value and Y the new value. Example: from 100 to 125 is (125 − 100) / 100 × 100 = +25%. The starting value must not be zero, because change relative to zero is mathematically undefined. The denominator uses |X| so a negative starting value keeps a clear direction of change.
Why does a percent increase followed by the same percent decrease not return to the start?
Because each step applies to a different base. From 100, a 20% increase gives 120; a 20% decrease from 120 applies to 120, giving 96. Percentages are relative, not absolute offsets.
Is my data uploaded anywhere?
No. The calculation runs entirely in your browser with plain client-side arithmetic. Your numbers never leave your device — nothing is stored, logged or uploaded.
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About this tool
This free percentage calculator answers the three questions people actually ask about percentages, all in one place and all as you type. Mode one: what is X% of Y — for tips, sales tax, discounts and commission. Mode two: X is what percent of Y — for exam scores, survey shares, budget breakdowns and progress toward a goal. Mode three: percent change from X to Y — for price movements, revenue growth, weight change and month-over-month metrics, with an explicit plus sign for increases and a minus sign for decreases. Every result is computed instantly in your browser the moment both numbers are filled in; there is no button to press and nothing is sent to a server, so salary figures, revenue data and grades stay entirely on your own device. Results are rounded to up to ten significant digits so you get exact values like 12.5% instead of drifting decimals. Whether you are double-checking a discount in a shop, preparing a report or doing homework, the three modes cover the everyday arithmetic of percentages without any signup.