Percentage Calculator

"Percentage calculator" is one of the most-searched phrases on the internet, but most tools behind that search only answer one specific version of the question — usually just "X% of Y." In practice, percentage questions come in at least eight distinct shapes, and figuring out which formula applies to your specific question is often the actual hard part, not the arithmetic itself.

This tool covers all eight: finding a percentage of a number ("what is 15% of 80?"), figuring out what percentage one number represents of another ("30 is what percent of 200?"), reverse-solving for the original total ("40 is 25% of what number?"), calculating the percentage change between two values ("price went from $80 to $95"), the symmetric percentage difference between two values when neither is clearly the "original" (useful for comparing two competing numbers), percent error for checking a measurement against an accepted true value, directly applying an increase or decrease to a number, and — the feature most percentage calculators skip entirely — chaining multiple percentage changes in sequence.

That last mode exists because of a genuinely common, costly mistake: "20% off, then an extra 10% off" is not 30% off. Each discount applies to the already-reduced price, so the real total works out to 28% off, not 30%. This tool shows both numbers side by side — the naive assumption and the actual sequential result — so the gap is visible, not just correctly hidden inside a right answer. It works the same way for stacked raises or markups, where the compounding effect goes the other way and quietly costs you more than the naive sum would suggest.

Every result shows its exact formula alongside the answer — not just the number, but the arithmetic that produced it. All eight modes calculate live as you type, with no submit button or page reload, and every calculation happens directly in your browser using plain JavaScript arithmetic — there's no server round trip for something this simple.