About Percentage Math

Percentages show up at the register, in a raise, on a test and in the news. Each tool here answers one percentage question in plain words and shows the formula next to the answer.

How we keep it accurate

Every number that comes from a law, a standard or a dataset links to the original source on the page where it is used. The math is shown next to each result so you can check it yourself. If you spot a mistake, the result shown on your screen is still yours to verify; we fix errors as soon as we find them.

How numbers are rounded

The math is done with exact fractions, so there is no floating-point drift. Money is rounded to the cent at each step, with half a cent rounding up. Percentages are shown to two decimal places and other numbers to four; when a shown answer is rounded, it says "about".

Free to use

The tools are free and need no sign-up. Ads from Google AdSense pay for keeping the site online. See the privacy policy for what that means.