Percentage Calculator
Find a percentage of a number, what percent one number is of another, the percentage change between two values, and the result of increasing or decreasing a number by a percentage.
Runs in your browser. What you enter here is not sent to our server.
The formulas
| Question | Formula | Example |
|---|---|---|
| What is X% of Y? | X ÷ 100 × Y | 15% of 80 = 12 |
| X is what % of Y? | X ÷ Y × 100 | 12 of 80 = 15% |
| Change from X to Y | (Y − X) ÷ X × 100 | 80 to 100 = +25% |
| X increased by P% | X × (1 + P ÷ 100) | 80 + 25% = 100 |
| X decreased by P% | X × (1 − P ÷ 100) | 100 − 20% = 80 |
A common trap
A percentage increase and the same percentage decrease do not cancel out. Going from 80 to 100 is a 25% increase, but going from 100 back to 80 is a 20% decrease, because each percentage is measured against a different starting number.
Likewise, a change from 10% to 15% is an increase of 5 percentage points, but a 50% increase in relative terms. Be clear which one you mean when reporting figures.
Questions about the Percentage Calculator
How do I work out a discount?
Use “decreased by”. For a price of 60 with 25% off, enter 60 and 25 to get 45.
How do I add tax or a tip?
Use “increased by”. For a bill of 40 with a 15% tip, enter 40 and 15 to get 46.
Why does it say “undefined” for a change from 0?
Percentage change divides by the starting value, and dividing by zero has no answer. A change from zero cannot be expressed as a percentage.