Percentage Calculator
Work out a percentage of a number, what percentage one number is of another, or a percentage increase or decrease — with the sum written out so you can check it.
Runs entirely in your browser — nothing is uploaded
Answer
16
20% × 80 ÷ 100 = 16
Five questions, not one box
The hard part of a percentage has never been the arithmetic. It is knowing which question you are asking, because several of them use the same two numbers and give completely different answers.
- 20% of 80 is 16.
- 20 is what percent of 80 is 25%.
- 80 increased by 20% is 96.
- 80 reduced by 20% is 64.
Four answers, one pair of numbers. A single input box cannot tell them apart, which is why each question is named here and written out as a sentence with the numbers inside it.
The working is shown for a reason
A bare number tells you nothing about whether you picked the right question, and picking the wrong one produces a confident, plausible, wrong answer. Seeing the sum written out is what catches that before you act on it.
Why a 25% rise is not cancelled by a 25% fall
Because the second percentage is taken from a larger number. 80 raised by 25% is 100; 100 reduced by 25% is 75, not 80. The same trap appears with a shop discount reversed at the till, and with an investment that falls 50% and then rises 50% — it is still down a quarter.
If what you want is the change between two figures you already have, use the change mode rather than doing it in two steps.
Percent and percentage points are different things
A rate moving from 4% to 5% has risen by one percentage point, and by 25 percent. Both are true and they sound identical, which is exactly why the distinction gets abused in headlines. The change mode gives you the percentage figure; the percentage point is simply the subtraction.
Nothing leaves this tab
The arithmetic happens in your browser, the numbers are never sent anywhere, and the page keeps working with the connection switched off. Nothing is stored between visits.
Frequently asked questions
Why are there five modes instead of one box?
Because the hard part of a percentage is never the arithmetic — it is knowing which question you are asking. “20% off 80” and “20 is what percent of 80” are different sums with different answers, 64 and 25, and no single input can tell them apart. Naming each question is the whole point.
Why does it show the working?
So you can check it rather than trust it. A number on its own tells you nothing about whether you picked the right mode, and a wrong mode gives a confident, plausible, wrong answer. Seeing the sum written out is what catches that.
Why is a 25% rise not cancelled by a 25% fall?
Because the second percentage is taken from a bigger number. 80 raised by 25% is 100; 100 reduced by 25% is 75, not 80. This catches people out constantly with discounts and with investment returns, and it is the reason percentage change has its own mode here.
What is the difference between percent and percentage points?
A rate going from 4% to 5% has risen by one percentage point, but by 25 percent. Both statements are true and they sound identical, which is why the difference is worth knowing. Use the change mode for the percentage figure; the percentage point is simply the subtraction.
Is anything sent anywhere?
No. The arithmetic happens in this tab, the numbers never leave it, and the page keeps working with the connection off. Nothing is stored between visits either.