Percentage calculator — ratio, change, and ±% in one tool
A general-purpose percentage tool with four modes: X% of Y, X as % of Y, percent change from A to B, and a value increased or decreased by N%. Use it for discounts, year-over-year change, success rates, custom tax rates, tips, or grade percentages — all in one screen. Live calculation, 0 to 10 decimal places, and one-click copy. Everything runs in your browser.
How to use
Pick one of four modes depending on what you want. Use 『X% of Y』 for discounts, sales tax, or tips. Use 『X is what % of Y』 for completion rates and shares. Use 『% change from A to B』 for year-over-year or month-over-month changes. Use 『X ± Y%』 for the value after a discount or markup. Type two numbers and the result updates live; choose decimal places and copy with one click.
FAQ
- Which mode should I pick?
- Want the actual amount of a percentage? Pick 『X% of Y』 (e.g. 8% of 1,000 = 80). Want the share? Pick 『X is what % of Y』 (e.g. 30 of 120 = 25%). Want the rate of change? Pick 『A → B』 (e.g. 100 → 120 = +20%). Want the value after the change? Pick 『X ± Y%』 (e.g. -20% off 5,000 = 4,000).
- Can I enter a negative Y%?
- Only in the 『X ± Y%』 mode. Enter -20 to apply a 20% discount. In 『A → B』 mode the sign comes automatically: negative when B < A.
- The result rounds to 0 — why?
- Tiny results like 0.0001 round to 0 at 0 decimal places. Increase 『Decimal places』 to 4 or more. For money amounts, 0 or 2 places are usually best.
- What happens if I divide by zero?
- 『X is what % of Y』 and 『% change from A to B』 modes show an error when Y or A is 0, since percentage is undefined.
- Is there a dedicated sales tax tool?
- Yes — for Japanese consumption tax with rounding modes (down / nearest / up) use the consumption-tax-jp tool. This tool is for general percentage math.
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