About the percentage calculator
Percentage change is the one people get wrong, because it is not symmetrical. Going from 50 to 75 is a 50% increase; going back from 75 to 50 is a 33.3% decrease. The base is always the value you started from.
The same asymmetry means a discount and a mark-up of the same percentage do not cancel. Adding 20% to 100 gives 120; taking 20% off 120 gives 96, not 100.
Frequently asked questions
- Is anything I enter sent anywhere?
- No. Every calculation runs inside your browser. Nothing you type - a date of birth, a salary, a list of numbers - is uploaded, stored or logged, and the page keeps working with the network disconnected.
- Why is a 20% rise then a 20% fall not back where I started?
- Because the second percentage is taken from a bigger number. 100 plus 20% is 120, and 20% of 120 is 24, so you land on 96. To reverse a 20% increase you need to take off 16.67%.
- What is the difference between percentage points and per cent?
- A rate going from 5% to 7% has risen by two percentage points, but by 40 per cent. Both are correct and they mean very different things, which is why the difference is worth stating whenever a rate changes.
- Why do I sometimes see a long string of decimals elsewhere?
- Because binary floating-point arithmetic cannot represent most decimal fractions exactly - 4.35 times 100 comes out as 434.99999999999994. Results here are tidied to twelve significant figures, which removes the noise without losing any precision you entered.
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How your data is handled
Everything happens on your device. There is no upload, no storage and no logging. Closing the tab clears everything you entered.