Work out a percentage

The three questions

X% of Y takes a percentage of a number: 20% of 150 is 30. Use it for a discount, a tip figured by hand, or a share of a total.

X is what percent of Y turns two numbers into a percentage: 30 out of 150 is 20%. Use it for a score, a portion of a budget, or how much of a goal is done.

Percent change compares a starting number to an ending one: 100 up to 125 is a 25% increase; 125 down to 100 is a 20% decrease. The starting number is always the base, which is why an increase and the matching decrease are not the same percentage.

Good to know

Answers are shown to a sensible number of decimals and trailing zeros are dropped, so a clean result reads clean. The underlying value is not rounded before the final line.

Percent change needs a non-zero starting number. Going up from zero has no percentage, because there is nothing to compare against; the tool says so instead of showing infinity.

Check for yourself that nothing is sent anywhere

You don't have to take our word for it. Every browser has a built-in panel that shows everything a page sends or receives over the internet. On a computer (this doesn't work on a phone):

1. Press F12, or right-click anywhere on this page and choose Inspect.
2. In the panel that opens, click the Network tab.
3. Now use the tool: type your numbers.
4. Watch the Network list. Nothing appears, because the numbers you type are never sent anywhere. The math runs entirely on your own computer.