Percentage Calculator
Work out what percentage one number is of another, apply a percentage increase or decrease, or find percentage change between two values — all calculated instantly on your device.
All calculations happen on your device — no numbers are sent to a server.
What this tool does
Works out percentages four different ways: a percentage of a number, what percentage one number is of another, the percentage increase or decrease between two values, and the reverse percentage that recovers an original from a changed value.
When to use it
- Working out a discount or tax amount from a price.
- Finding what percentage your score is of the total.
- Measuring the rise or fall between two figures — two months' sales, say.
- Finding the pre-discount price when you know the price after it and the rate.
How to use it
- Choose the "Calculation type" from the four forms.
- Fill in the fields that appear for that type.
- Read the result immediately.
A practical example
Input
"Percentage increase/decrease" with an original value of 80 and a new value of 100.
Output
A 25% increase — because the change is measured against the original value, not the new one.
This is where people most often go wrong: falling from 100 to 80 is a 20% drop, but rising from 80 to 100 is a 25% rise. The base differs.
Limitations
- The reverse percentage needs the rate of change exactly; an approximate rate gives an approximate original.
- Successive discounts do not add up as percentages — use the Discount Calculator, which handles the stacking.
- This calculates and saves nothing.
Privacy and processing
All calculations happen on your device and no numbers are sent to a server.
Technical notes
- The four forms are kept separate in the interface deliberately, because confusing a percentage of a number with a reverse percentage is the single commonest source of error in percentage work.