Percentage Calculator

The Percentage Calculator solves the three percentage questions people ask most often: what is X percent of a number, one number is what percent of another, and the percentage increase or decrease between two values. Type your numbers, pick the calculation, and the answer appears instantly along with the exact formula used to reach it.

Percentages trip people up because each question uses a different formula. Finding a tip means multiplying by a percent, working out a discount rate means dividing, and measuring growth means comparing a change against the original amount. This tool keeps the three operations separate and clearly labeled so you always apply the right one - no memorizing formulas, no spreadsheet, no mental arithmetic.

Every calculation runs entirely in your browser. Nothing you type is sent to a server, the tool works offline once the page has loaded, and there is no signup or usage friction. Results are rounded to four decimal places to stay readable while avoiding the floating-point rounding noise that plain JavaScript math often produces.

Two things about percentages trip people up regularly, and both are easy to check here. A percentage increase and the same percentage decrease do not cancel: 100 raised by 10 per cent is 110, and 110 reduced by 10 per cent is 99, because each is taken from a different base. And a change from 20 per cent to 25 per cent is a rise of five percentage points but of 25 per cent, which is why reports that say only "up 25 per cent" are so often misread. The formula is shown with every answer so you can see which base was used. Dividing by zero is caught rather than returning infinity, since a percentage of nothing has no meaningful value.