Percentage Calculator
Calculate what a percentage is in absolute terms, what percentage one number is of another, what the whole is when you know the part and the percentage, or how large a percentage change is.
How to use the percentage calculator
- Choose which type of percentage calculation you need with the buttons above the calculator.
- Enter your numbers — the calculator works out the answer automatically as you type.
- Read the explanation below to understand how the answer was calculated.
How percentages are calculated
Percent means "per hundred", and every percentage calculation builds on the same base formula:
To find what X % of Y is, rearrange the formula: take the percentage divided by 100, and multiply by the number. To find 20 % of 850, you calculate 20 ÷ 100 × 850 = 170.
To find what percentage A is of B, use the base formula directly: 170 ÷ 850 × 100 = 20 %.
To reverse the calculation — you know the part and the percentage, but want the whole — flip the "X % of Y" formula around: divide the part by the percentage (as a fraction). If 170 makes up 20 % of a number, that number is 170 ÷ (20 ÷ 100) = 850.
To find a percentage change between two numbers, use the formula (new value − old value) ÷ old value × 100. If a number goes from 850 to 1020, the change is (1020 − 850) ÷ 850 × 100 = 20 % increase.
Frequently asked questions
How do I calculate a percentage discount?
Use the "X % of Y" tab. Enter the discount percentage and the original price — the result shows how much you save. Subtract this from the original price to find the new price.
Can I calculate a negative percentage change?
Yes. Use the "% change" tab. If the number decreases, the calculator shows a negative percentage, meaning a decline.
What's the difference between percentage points and percent?
Percentage points are the direct difference between two percentage shares (e.g. from 20 % to 25 % is 5 percentage points), while percent change calculates how large the relative change is (5 ÷ 20 × 100 = 25 % increase).
I know 170 is 20 % of a number — how do I find the number?
Use the "Reverse %" tab. Enter 170 as the part and 20 as the percentage — the calculator works out that the whole is 850. This is useful when you know a discount amount and the discount percentage, for example, and want to find the original price.