How to use the percentage Calculator
- Choose the kind of percentage question you want to answer. The letters X and Y in the question match the two boxes.
- Enter X and Y. Decimals and negative numbers are fine.
- The result updates instantly as you type. There is no button to press.
- Use Copy result to copy the figures, or Copy link to share a link that reopens the percentage Calculator with the same inputs.
How it works
"Per cent" means "per hundred", so a percentage is just a fraction with 100 as the bottom number: 20% means 20 out of every 100, or 0.2. Almost every percentage question is a rearrangement of one relationship, part = percent × whole, and this calculator handles each version of it.
What is X% of Y? finds a part, such as a 15% tip on a bill or 20% of a class. X is what percent of Y? compares a part with the whole, such as a test score of 42 out of 50. X is Y% of what? works backwards from a part to the whole, which is handy when you know a deposit was 10% of a price and need the full price. The last two options increase or decrease a number by a percentage, as with a pay rise, a price increase or a discount.
A common mistake is assuming a percentage increase and the same percentage decrease cancel out. They don't: raise 100 by 10% to get 110, then cut 10% and you get 99, because the second 10% is taken from a larger number. For the percentage difference between two values, use the percentage change calculator.
Formula
To turn a percentage into a decimal, divide by 100 (35% = 0.35). To turn a decimal into a percentage, multiply by 100.
Example
What is 20% of 150? 20 ÷ 100 × 150 = 30. 30 is what percent of 150? 30 ÷ 150 × 100 = 20%. 30 is 20% of what? 30 ÷ 0.20 = 150. Increasing 150 by 20% gives 150 × 1.2 = 180, and decreasing it by 20% gives 150 × 0.8 = 120.
Frequently asked questions
How do I calculate a percentage in my head?
Find 10% by moving the decimal point one place left, then scale. For 15% of 80: 10% is 8, 5% is 4, so 15% is 12. For 1%, move the decimal two places.
Is X% of Y the same as Y% of X?
Yes. 8% of 50 equals 50% of 8, both 4. Swapping the numbers is a handy shortcut for mental maths.
Why doesn't +10% then −10% get me back to the start?
Because each percentage is taken from a different base. After a 10% rise the number is bigger, so 10% of it is more than the original increase.