Percentage Calculator

The Percentage Calculator answers the three percentage questions everyone eventually runs into: what is X% of Y, what percentage of Y is X, and what is the percentage change from one number to another. Instead of remembering which way to divide or multiply, you pick a mode, type your two numbers, and read the answer immediately — it's the fastest way to find a percent of any total without opening a spreadsheet or reaching for a formula sheet.

It's built for the calculations that come up constantly in everyday life and at work: figuring out a restaurant tip, applying a storewide discount, calculating sales tax on a purchase, working out a commission rate, checking a grade score as a percentage, or tracking how much a metric moved between two reporting periods. Each mode updates its result live as you type, so you can nudge a number up or down and immediately see how the answer shifts — useful for comparing several discount scenarios or tip amounts side by side.

The math behind each mode is simple once written out. 'X% of Y' multiplies Y by X/100. 'X is what percent of Y' divides X by Y and multiplies by 100. Percentage change subtracts the old value from the new value, divides by the old value, and multiplies by 100 — a positive result means an increase, a negative result means a decrease. The calculator handles decimals and negative numbers in all three modes, so it works equally well for a small percent of a number and for large percentage change swings in financial or scientific data.

Because everything runs locally in the browser, there's nothing to install and nothing sent to a server — just type your numbers and get the answer. It's free with no usage limits, and it works the same way on a phone, tablet or desktop, which makes it a reliable default for any quick percent-of-a-number or percentage-change question.