Percentage Calculator
Pick the question you are asking, enter your two numbers, and read the answer with the working shown. Five percentage sums, one calculator.
How to use this calculator
- Choose your question from the dropdown. Each one is written out with
AandBin it, so you can see which number goes where. - Enter
Aas the first number andBas the second. For "What is A% of B?" that means the percentage first and the amount second. - Read the answer, then check the question line under the inputs and the working shown with the result. They repeat your sum in words and in figures, which is the quickest way to catch two numbers entered the wrong way round.
Nothing is submitted anywhere. The calculation runs in the page as you type, and the address bar carries your figures, so a result can be shared or bookmarked.
How percentages are calculated
A percentage is a fraction of 100 — per cent means "per hundred". Every percentage sum is therefore the same two steps in a different order: turn the percentage into a decimal by dividing by 100, then multiply or divide by it.
- Percentage — the rate you are applying, e.g. 15
- Number — the amount you are applying it to, e.g. 200
- Result — the answer, e.g. 30
Reversing the sum answers the other questions. Dividing the part by the whole gives the rate instead of the amount, and dividing the amount by the rate gives the whole back.
| Question | Formula | Example |
|---|---|---|
| What is A% of B? | A ÷ 100 × B | 15% of 200 = 30 |
| A is what percent of B? | A ÷ B × 100 | 1,245 out of 4,000 = 31.125% |
| A is B% of what? | A ÷ (B ÷ 100) | 10 is 5% of 200 |
| A increased by B% | A × (1 + B ÷ 100) | 5 increased by 30% = 6.50 |
| A decreased by B% | A × (1 − B ÷ 100) | 80 decreased by 25% = 60 |
The last two rows are the ones worth reading twice. Adding 30% to 5 gives 6.50 because the multiplier is 1.3, and taking 30% back off 6.50 gives 4.55 rather than 5 — the second percentage is taken from a larger number, so the two do not cancel out.
A worked example
A £4,000 monthly budget includes £1,245 of rent. To find what share the rent takes, choose "A is what percent of B?", enter 1,245 and 4,000, and the calculator divides one by the other:1,245 ÷ 4,000 = 0.31125, then multiplies by 100 to give 31.125%.
Working the same figures the other way is the third question. If you know rent is 31.125% of the budget and comes to £1,245, then 1,245 ÷ 0.31125 = 4,000 recovers the budget. Any two of the three numbers give the third.