Percent of a Number Calculator
The percent of a number calculator answers the question "What is X% of Y?" Enter a percentage and a number, and the calculator returns the result. For example, 20% of 100 is 20. This is one of the most common percentage calculations in everyday life. The formula is straightforward: result = number * percentage / 100. The calculator also includes a reverse mode: given a result and a percentage, find the original number. For example, if 20% of a number is 30, the number is 150. Percent of a number calculations are essential for computing discounts, sales tax, tips, interest payments, and many other practical applications.
Percent of a number formula
Result = number * percentage / 100
Or: result = number * (percentage / 100)
Common examples
| Percentage | Number | Result | Real-world context |
|---|---|---|---|
| 20% | 100 | 20 | Discount on 100 dollar item |
| 15% | 50 | 7.50 | Tip on 50 dollar bill |
| 8.5% | 200 | 17.00 | Sales tax on 200 dollar purchase |
| 3% | 1,000 | 30.00 | Annual interest on 1,000 dollars |
| 50% | 80 | 40 | Half of 80 |
Percent of a number calculator: frequently asked questions
What does 'percent of a number' mean?
When you ask 'What is 20% of 100?', you are calculating a portion of a number. The answer is 20, because 20% (or 0.20) of 100 is 100 * 0.20 = 20. This calculation is useful for finding discounts, tips, sales tax, interest, and many other real-world applications.
How do I calculate a percent of a number?
The formula is: result = number * percentage / 100. For example, to find 15% of 80, calculate 80 * 15 / 100 = 12. Alternatively, convert the percentage to a decimal (15% = 0.15) and multiply: 80 * 0.15 = 12.
Can I reverse the calculation?
Yes. If you know the result and the percentage, you can find the original number: original = result / (percentage / 100). For example, if 20% of a number is 30, the original number is 30 / 0.20 = 150. This calculator can work in reverse mode.
What is the difference between 'percent of a number' and 'what percent'?
'Percent of a number' answers 'What is 20% of 100?' (answer: 20). 'What percent' answers 'What percent of 100 is 20?' (answer: 20%). They are reciprocal questions that use different formulas.
When would I use this calculation?
Common uses include calculating sales discounts (What is 25% off a 100 dollar item?), tips (What is 18% of a 50 dollar bill?), taxes (What is 8.5% sales tax on 200 dollars?), and interest (What is 3% of 1,000 dollars in annual interest?).
Official sources
- Standard mathematical formula for percent of a number.
- NIST Special Publication 330: The International System of Units.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.