How this percentage calculator works
This tool covers the three most common percentage problems in one place: finding a percent of a number, finding what percent one number is of another, and finding the percentage increase or decrease between two numbers.
percent of a number = (percent ÷ 100) × numberX is what percent of Y = (X ÷ Y) × 100percentage change = ((new − old) ÷ old) × 100
For the percentage change calculator, a positive result is an increase and a negative result is a decrease — the calculator labels the result accordingly.
A note on rounding
Results are rounded to two decimal places for readability. The underlying calculation uses the exact values you enter, so very small rounding differences compared with other tools are expected and not an error.
Frequently asked questions
How do I calculate a percentage of a number?
Divide the percentage by 100, then multiply by the number. For example, 20% of 50 is (20 ÷ 100) × 50 = 10. Use the first calculator above and enter the percent and the number.
How do I find what percent one number is of another?
Divide the first number by the second, then multiply by 100. For example, 10 is what percent of 50 is (10 ÷ 50) × 100 = 20%. Use the second calculator above for this.
How is percentage increase or decrease calculated?
Subtract the old value from the new value, divide by the old value, then multiply by 100. For example, going from 50 to 60 is ((60 − 50) ÷ 50) × 100 = 20% increase. If the result is negative, it's a percentage decrease.
Why can't the starting number or the "whole" be 0?
Both formulas divide by that number, and division by zero is undefined. Enter a non-zero value for the second number in the "what percent of" calculator, and for the starting value in the percentage change calculator.
What's changed
- Launched.
References
- Common Core State Standards — Ratios & Proportional Relationships (Grade 6)
a percent of a quantity is a rate per 100, so 30% of a quantity means 30/100 times that quantity