Percentage Calculator
Four percentage modes: percent of a number, what percent, change rate and increase or decrease.
Result = X × Y ÷ 100
Result = X ÷ Y × 100 (%)
Result = (Y − X) ÷ X × 100 (%)
Result = X × (1 ± Y ÷ 100)
How to use it
- Pick one of the four modes above the inputs.
- Enter X in the first field and Y in the second. Decimals and negative numbers are accepted.
- In the "X +/- Y%" mode, choose increase or decrease from the dropdown.
- The result updates as you type, and the formula line shows which expression is used.
- Use Clear to reset both fields.
Common use cases
- Shopping and discounts - a 30% discount on a price, or the price after a markup.
- Grades and statistics - a score as a percentage of the maximum, or a pass rate.
- Finance and reports - month-over-month change rates, tax and fee percentages.
- Growth tracking - how much a number grows or shrinks after a percentage change.
Why it stays private
All four modes run as simple arithmetic in your browser. No input ever leaves the page, nothing is stored, and there is no network request.
FAQ
Q: How is the change rate calculated when X is negative? A: The formula is (Y - X) / X * 100. With a negative base the sign follows the math directly, so double-check the direction of change in that case.
Q: Why does the "X is what % of Y" mode reject Y = 0? A: Division by zero is undefined, so the tool shows an error instead of a misleading result.
Q: Does the tool round the results? A: Display is limited to six decimal places for readability, but the underlying calculation keeps full floating-point precision.
Your data stays on this device
Percentage Calculator runs 100% locally. Everything you paste or drop is processed by your own browser and never transmitted. Nothing is stored on our servers — close the tab and it is gone.
Nothing you type is sent to a server, logged, or used for analytics. The page works even with your network disconnected after first load.