Percentage Calculator

Five separate calculations sit behind the buttons at the top of the page, and each one keeps its own numbers so you can switch between them without retyping anything.

"What is X% of Y" divides the percentage by 100 and multiplies by the number. "X is what percent of Y" divides the part by the whole and multiplies by 100. Those two answer most everyday questions: a tip on a bill, a commission on a sale, a score out of a total.

Percentage change and percentage difference look alike but answer different questions, and confusing them is the most common mistake people make with percentages. Change assumes one number came first and measures the gap against that starting value, so 120 to 150 is a 25% rise. Difference treats both numbers as equals and divides by their average instead, which gives 22.22% for the same pair. Use change for before-and-after figures and difference for two independent readings.

The increase and decrease calculator applies a rate to a starting number and reports both the new figure and the amount that moved, which is what you need for discounts, markups, tips, and tax.

Nothing is rounded until a result is displayed, and the display keeps up to four decimal places with trailing zeros stripped. Under every answer the tool prints the exact arithmetic it ran, so you can copy the working into homework, an invoice, or a spreadsheet formula and check it line by line.