Percentage Calculator
Calculate X% of Y, find what percent A is of B, measure percent change, or increase and decrease by a percent.
About this calculator
Four everyday modes cover percent of, what percent, percent change, and increase or decrease by a percent. The active formula stays visible so the arithmetic matches what you see.
Bases of zero are rejected for “is what percent” and percent change, with a clear field error instead of Infinity. Calculations use ordinary JavaScript numbers; results round only when displayed or copied (up to six significant figures, or scientific notation for very large or tiny values).
Everything runs in your browser. Inputs are not saved, shared in the URL, or sent to a server. Results are arithmetic assistance only—not financial, legal, or grading advice.