Percentage Calculator

This Percentage Calculator splits the three percentage problems most people actually run into into three clearly labeled modes, so you never have to remember which number divides which. Mode one, "what is X% of Y," takes a rate and a total: type 15 and 80 and it shows that 15% of 80 is 12 — the calculation behind a tip, a sales discount, a sales-tax line, or a commission cut. Mode two, "X is what percent of Y," runs the division the other direction: enter 12 and 80 and it returns 15%, which is how you express a score, a market share, or how much of a monthly budget a single expense ate up. Mode three measures change between two numbers against the first one as the baseline: 80 to 100 reads as a 25% increase, while 100 to 80 reads as a 20% decrease. Because the starting value sets the base, the tool makes plain that those two moves are not mirror images — a distinction people routinely get wrong when doing it in their head.

The math runs entirely in your browser in JavaScript. Each keystroke recomputes the answer on your own device; nothing you type is uploaded, logged, or sent anywhere, so salaries, invoice totals, or medication doses stay on your screen and nowhere else. There is no account to create, and once the page has loaded it keeps working with the network off.

A few concrete habits it rewards: to price a "30% off" item at $80, use mode one to get 24 off, then subtract for a $56 total. To check whether a percent-off deal beats a flat coupon, compute both amounts and compare. And in change mode, remember that a 50% drop followed by a 50% rise lands you at 75, not back at 100 — the calculator prevents exactly that error by always anchoring to the correct base. Percentages are easy to invert or apply to the wrong number; naming each mode removes that ambiguity in a single click.