What is X% of Y?
Divide the percentage by 100 and multiply. 15% of 80 = 0.15 × 80 = 12. A quick way to find 10% is to move the decimal point one place left; 5% is half of that.
X is what percent of Y?
Divide X by Y and multiply by 100. 18 out of 24 = 18 ÷ 24 × 100 = 75%.
Percentage change
Subtract the old value from the new one, divide by the old value and multiply by 100. A price going from 40 to 50 is (50 − 40) ÷ 40 × 100 = 25% more. From 50 back to 40 is a 20% decrease, because the starting point is now larger.
Adding or removing a percentage
- Add 20%: multiply by 1.2. 50 × 1.2 = 60.
- Take 20% off: multiply by 0.8. 50 × 0.8 = 40.
- Find the price before 20% tax was added: divide by 1.2. 60 ÷ 1.2 = 50.
Percent vs percentage points
If an interest rate rises from 4% to 5%, it has gone up by 1 percentage point, but by 25% in relative terms. News reports often mix the two up.
Skip the maths
The Percentage Calculator does all three calculations as you type.