Percentage calculator
Three common percentage questions, each with its formula.
Values
Enter plain numbers. A denominator cannot be zero.
Result
No result yet. Enter both values and select Calculate percentage.
Formulas
- Percent of a value: result = value × percentage ÷ 100. Example: 15% of 200 = 30.
- X as a percentage of Y: result = X ÷ Y × 100. Example: 30 of 200 = 15%. Y = 0 is rejected because the ratio is undefined.
- Percentage change: result = (new − old) ÷ old × 100. Example: 80 to 100 = +25%; 100 to 80 = −20%. A starting value of 0 is rejected because change from zero has no finite percentage.
Zero and negative values
Zero is a legitimate value when it is not the denominator: 15% of 0 is 0, and 0 is 0% of 200. Negative percentages and negative changes are allowed where the formula permits them. The tool does not apply tax, interest, discounts or financial advice.
Precision
Inputs accept plain decimal or exponent notation with up to 15 significant digits and a magnitude of at most 1,000,000,000,000,000. Results are shown with at most 12 decimal places (or exponential notation for very small or large values), so a repeating value is rounded for display. The result also carries its raw numeric value for automated checks.
Example
Example
At 15% of 200 the result is 30. If 30 is compared with 200 instead, the answer is 15%. Moving from 80 to 100 is a +25% change.