How to Calculate the Percentage of a Number
Almost every everyday percentage question is one of two shapes. Both come from the same idea: a percent is a number out of 100.
1. What is X% of Y?
Turn the percent into a decimal and multiply. 15% of 80 = 0.15 × 80 = 12. A tip, a tax, or a commission all work this way.
2. X is what percent of Y?
Divide, then multiply by 100. On a test, 16 out of 20 = 16 ÷ 20 = 0.8 = 80%. 24 out of 30 is also 80%, and 11 out of 15 is about 73.33%.
A handy symmetry
X% of Y always equals Y% of X. So 8% of 50 is the same as 50% of 8, which is 4. Flip the question when one side is easier.
When the number changes
If you are comparing an old and a new value, you want a percent change instead: (new − old) ÷ old × 100. The percent change calculator labels the result as an increase or decrease.
Try it with your own numbers.
Open the percentage calculator