Percentage Calculator
Percent of a number, what percent one number is of another, and percentage change.
How to use Percentage Calculator
- Choose the question you want to answer.
- Enter X and Y.
- Read the answer and the formula used.
How it works
Percent means "per hundred". The calculator uses: X% of Y = X ÷ 100 × Y; X as a percent of Y = X ÷ Y × 100; percentage change = (new − old) ÷ |old| × 100; increase = Y × (1 + X/100) and decrease = Y × (1 − X/100).
A percentage change is not symmetric: going from 100 to 150 is +50%, but going back from 150 to 100 is −33.3%. That is why a 50% loss needs a 100% gain to recover.
Example
15% of 240 = 0.15 × 240 = 36. A price that rises from 80 to 100 has increased by (100 − 80) ÷ 80 = 25%.
Frequently asked questions
How do I calculate a discount?
Choose "Y decreased by X%": a 20% discount on 59.99 gives 47.99. The saving is 20% of 59.99 = 12.00.
What is the difference between percent and percentage points?
If an interest rate rises from 4% to 5%, that is 1 percentage point but a 25% increase.
Why is percentage change from 0 undefined?
Dividing by zero is undefined: any increase from zero is infinitely large in percentage terms.
Can X or Y be negative or decimal?
Yes. Decimals and negative numbers work; change uses the absolute value of the starting number.
Limitations
- Results are rounded to 6 significant decimals for display.
- Percentage change from 0 cannot be calculated.
Last reviewed November 9, 2026. How we build and test tools.