What it does
This calculator works out a percentage of a number — for example, what 15% of 240 comes to. Type a percentage and a value and the answer appears as you go; there is no button to press and nothing is sent to a server.
How it works
A percentage is just a fraction out of 100. To find a percentage of a value, you turn the percentage into a decimal (divide it by 100) and multiply:
Dividing by 100 rescales the percentage to a proportion between 0 and 1, and multiplying applies that proportion to your value. It is the same arithmetic whether you are taking 20% off a price or adding 2.5% interest.
Worked example
Take 15% of 240. First convert the percentage to a decimal: 15 ÷ 100 = 0.15. Then multiply by the value: 0.15 × 240 = 36. So 15% of 240 is 36.
- 20% of 50 is 10 —
20 ÷ 100 × 50 = 10. - 12.5% of 64 is 8 — a fractional percentage works exactly the same way once it is written as a decimal (12.5 ÷ 100 = 0.125).
"Percentage of" vs percentage change and percentage points
This calculator answers one specific question — what is X% of a number. That's a different question from how much a number has changed in percentage terms, and different again from a percentage point, which is a plain difference between two percentages rather than a ratio. If a savings rate moves from 5% to 7%, that's a rise of 2 percentage points, but a 40% relative increase (2 ÷ 5 × 100), because a percentage-point figure is measured against the earlier percentage, not zero. Confusing the two is one of the most common percentage errors in news reporting and pricing — see our guide to percentage change vs percentage points for the full breakdown, including how to calculate a percentage change from a before-and-after value.
Increases and decreases don't cancel out
Increasing a value by a percentage and then decreasing the result by the same percentage does not return you to the original number, because the second percentage is taken from a different, larger base. £100 increased by 20% is £120; decreasing £120 by 20% is £96, not £100, because that 20% is now calculated on the bigger figure. This trips people up on sale pricing ("20% off, then 20% added back on") and on any pair of sequential percentage changes reported in statistics. To reverse a percentage increase precisely, divide by (1 + rate) rather than subtracting the same percentage back off.
Common uses
- Discounts: a "15% off" label on something priced 240 means a saving of 36.
- Tips and service: working out a 10% or 12.5% tip on a restaurant bill.
- Tax and interest: adding VAT, or estimating interest on a balance.
- Test scores and stats: turning "36 out of 240" into a percentage, or the reverse.
Frequently asked
How do I find what percentage one number is of another?
Divide the part by the whole and multiply by 100. For example, 36 out of 240 is (36 ÷ 240) × 100 = 15% — the inverse of the worked example above.
Can I use decimals, like 2.5%?
Yes. Fractional percentages work exactly the same way: 2.5% of 1000 is 0.025 × 1000 = 25.
What is 100% of a number?
100% of any value is the value itself, because dividing 100 by 100 gives 1, and multiplying by 1 changes nothing.
What's the difference between a percentage and a percentage point?
A percentage point is a plain arithmetic difference between two percentages, while a percentage change is that difference expressed relative to the starting figure. Going from a 5% rate to a 7% rate is a 2 percentage point rise, but a 40% percentage increase. See our guide to percentage change vs percentage points for worked examples both ways.
If I increase a number by 20% and then decrease it by 20%, do I get back to the start?
No. The decrease is calculated on the larger, already-increased figure, so you end up below where you started — £100 up 20% is £120, then down 20% is £96. The same asymmetry applies to any matched increase-then-decrease pair, in either order.
Can a percentage be more than 100%?
Yes. Percentages above 100% are normal whenever the part is larger than what you're comparing it to — 150% of 40 is 60, which is useful for expressing growth, markups or ratios that exceed the original amount.