How do percentages work?
A percentage expresses a part of a whole as a fraction of 100. To find X% of Y, multiply Y by X and divide by 100. To find what percent one number is of another, divide the part by the whole and multiply by 100.
Percentage change compares a new value to an old one: (new − old) ÷ old × 100. A positive result is an increase, a negative one a decrease. The same maths is behind discounts, sales tax and interest.
How to use the Percentage Calculator
- 1Choose the kind of percentage calculation.
- 2Enter the two numbers. Commas and dots both work as decimal separators.
- 3Read the result and the formula below it.
Frequently asked questions
How do I calculate a discount?
Use "Decrease Y by X%". For 20% off 80, enter 20 and 80 to get 64.
How do I calculate percentage change?
Use "Change from X to Y". Going from 50 to 65 is a 30% increase.
Why is a 50% increase followed by a 50% decrease not back to the start?
The second percentage applies to the new, larger number. 100 → 150 → 75.