A percentage expresses a number as a fraction of 100. This calculator covers three common percentage questions using the same simple formulas shown below.
How to use the percentage calculator
- Enter a percentage and a number in the first row, then click Calculate to find the percentage amount.
- Enter a part and a whole in the second row, then click Calculate to find what percentage the part represents.
- Enter the starting and ending values in the third row, then click Calculate to find the percentage increase or decrease.
Percentage formulas and examples
1. What is X% of Y?
Example: 25% of 200 = (25 ÷ 100) × 200 = 50.
2. X is what percent of Y?
Example: 30 is what percent of 200? (30 ÷ 200) × 100 = 15%. The whole value must not be zero.
3. Percentage increase or decrease
Example: A value rising from 80 to 100 changes by ((100 − 80) ÷ 80) × 100 = 25% increase. A value falling from 100 to 80 changes by −20%, or a 20% decrease. Percentage change is undefined when the original value is zero.
Where are percentages used?
Percentages are used to calculate sale discounts, tax, tips, school marks, salary changes, business growth, interest rates, and changes in prices or quantities. Always check which value is the reference or starting value before interpreting a percentage.
Frequently asked questions
What is a percentage?
A percentage is a way to express a number as a fraction of 100. For example, 25% means 25 out of every 100.
How do I calculate a percentage of a number?
Divide the percentage by 100 and multiply it by the number. For example, 20% of 150 is (20 ÷ 100) × 150 = 30.
How do I find what percent one number is of another?
Divide the part by the whole and multiply by 100. For example, 30 is 15% of 200.
How do I calculate percentage increase or decrease?
Subtract the original value from the new value, divide by the absolute original value, and multiply by 100. A positive result is an increase and a negative result is a decrease.
Why is percentage change undefined when the starting value is zero?
The formula divides by the original value. Division by zero is undefined, so report the absolute change instead when the starting value is zero.