Quick example
What is 15% of 200?
Convert 15% to its decimal form by dividing by 100, then multiply by 200. The calculation is (15 ÷ 100) × 200 = 30, so 15% of 200 is 30.
Three formulas
How to calculate percentages
Find X% of Y
Divide the percentage by 100 and multiply by the value: (X ÷ 100) × Y.
Find what percent X is of Y
Divide the part by the whole and multiply by 100: (X ÷ Y) × 100.
Find percentage change
Subtract the start from the end, divide by the start, and multiply by 100: ((end − start) ÷ start) × 100.
Read the sign
A positive percentage change is an increase. A negative result is a decrease, and zero means the value did not change.
Increase and decrease
How percentage change differs from the numeric difference
Moving from 80 to 100 is a numeric increase of 20. Relative to the starting value, that difference is 20 ÷ 80 = 0.25, or a 25% increase. Reversing the values—from 100 to 80—is a 20% decrease because the starting value is now 100.
Zero and rounding
When a percentage is undefined
“What percent?” and percentage-change calculations divide by a whole or starting value. That denominator cannot be zero. The calculator keeps useful precision for decimal answers, but displayed results may be rounded; calculations use the full JavaScript number before formatting.
Common questions
Percentage calculator FAQ
How do I calculate a percentage of a number?
Divide the percentage by 100, then multiply by the number. For example, 15% of 200 is 0.15 × 200, or 30.
How do I find what percentage one number is of another?
Divide the part by the whole and multiply by 100. For example, 30 ÷ 200 × 100 equals 15%.
How do I calculate percentage increase or decrease?
Subtract the starting value from the ending value, divide by the starting value, and multiply by 100. The sign shows whether it increased or decreased.
Why can the starting or whole value not be zero?
The formulas require division by that value. Division by zero is undefined, so no finite percentage result exists.