About PercentCalc

PercentCalc exists because percentage questions are easy to get wrong in a specific way: the arithmetic is trivial, but picking the wrong base — the new value instead of the old, the average instead of the starting point — quietly changes the answer. So every calculator here does two things: it picks the right formula for the question you picked, and it shows that formula and the working under the result, so you can check the answer instead of trusting it.

The family covers the six core question shapes (percent of, what percent, change, increase by, decrease by, difference), plus the everyday special cases people actually search for: discounts, marks percentages, and fraction-to-percent conversion. All calculations run locally in your browser; see the privacy page for exactly what that means.

PercentCalc is part of a small family of free tools. Pro features (batch calculations, history, embeds) are planned at $9/month and are not yet on sale — everything on the site today is free.