Percentages trip people up because the same word covers a few different questions. This tool keeps them separate, so you pick what you mean and get a clean answer.

The three modes

% of — a slice of a number. 15% of 80 is 12.
is what % — how big one number is next to another. 12 is 15% of 80.
% change — how much something rose or fell. 80 to 100 is a 25% increase; 100 to 80 is a 20% drop.

Why the direction matters

A 25% rise followed by a 25% fall does not return you to the start — the second percentage is taken from a bigger number. The change mode makes that asymmetry obvious, which is handy for prices, tips, and discounts.