Percentage Calculator

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A fast, no-nonsense percentage calculator that covers the three questions people actually ask. Switch between modes to find what Y% of a value is (like 20% of 150), figure out what percent one number is of another (30 is what percent of 150?), or measure the percentage increase or decrease between a starting and ending value (from 100 to 150 is a 50% increase). Results update as you type, with a plain-language summary of each calculation and one-click copying. Everything runs entirely in your browser — no numbers are uploaded — so it is private, instant, and works offline. Handy for discounts and sale prices, tips and tax, grades and test scores, markups and margins, growth rates, and any quick mental-math check you would otherwise reach for a spreadsheet to do.

of

Result

30

20% of 150 = 30

How to use

Pick a calculation type at the top: '% of a value', 'X is what % of Y', or '% increase / decrease'. Enter your two numbers in the labelled fields and the result appears immediately below, along with a sentence describing what it means. Use the copy button to grab the result. Switching modes keeps the numbers you already typed, so you can explore the same figures different ways.

Frequently asked questions

How do I calculate a percentage of a number?
Use the '% of a value' mode: enter the percentage and the value, and the tool multiplies them. For example, 20% of 150 is 30, because 150 × 20 ÷ 100 = 30. This is the calculation you want for discounts, tips, tax, and commissions.
What is the difference between 'what percent' and 'percentage change'?
'X is what % of Y' tells you how big one number is relative to another as a share of the whole — 30 out of 150 is 20%. 'Percentage change' measures how much a value grew or shrank from a starting point — going from 100 to 150 is a 50% increase, and going from 100 to 80 is a 20% decrease. Use the first for proportions and the second for growth or reduction over time.
Can the result be more than 100% or negative?
Yes. A part can exceed its whole (300 is 200% of 150), and a percentage change is negative whenever the value drops (100 to 80 is -20%). The only undefined cases are dividing by zero — asking what percent something is of zero, or the change from a starting value of zero — and the tool flags those instead of showing a misleading number. All math happens locally in your browser and nothing is sent to a server.