How do you calculate a percentage of a number?

Divide the percentage by 100 and multiply by the number: 15% of 200 is (15 / 100) × 200 = 30. The calculator also finds what percent one number is of another and the percentage change between two values, and shows the formula under every result.

Is my data sent to a server?

All calculations run entirely in your browser using JavaScript. Our servers are not involved at any point.

Can I calculate VAT or sales tax?

Yes. Use the percentage of a number calculator, enter the pre-tax amount and the tax rate to get the tax amount, then add it to the original for the total.

How do I calculate a percentage decrease?

Use the percentage change calculator. If the new value is less than the original, the result will be negative, showing the percentage decrease.

Percentage calculator

Percentage calculator is a calculator tool that solves the three most common percentage problems. It computes X% of Y, finds what percent X is of Y, and measures percentage change between two values, showing the formula alongside the result. The tool runs in your browser.

Percentage (%)Of number

Enter both numbers to see the result

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Calculation modes

Direct links for each type of percentage calculation.

What is X% of Y?

Calculate what X percent of a number is, such as 15% of 200 = 30. The formula is shown under the result so you can check it. Runs in your browser.

X is what % of Y?

Find what percentage one number is of another, such as 30 is 15% of 200. The formula is shown under the result, which you can copy. Runs in your browser.

Percentage change calculator

Calculate percentage increase or decrease between two values. Shows the exact change and direction. Free, in-browser.

How to calculate a percentage

Choose the calculation type, percentage of a number, percentage change, or what percentage one number is of another.
Enter the values into the appropriate fields.
The result updates instantly as you type.
Click “Copy result” to copy the result to your clipboard.

Common uses

Calculating discounts and sale prices when shopping, or stacking a coupon on top of a sale
Working out percentage change between two values for reports or data analysis, after you count the days between the two measurements
Finding what percentage a part is of a whole for statistics or grades

Technical specification

Algorithm or formula: Three modes of pure arithmetic. X% of Y: (X/100) * Y. X is what % of Y: (X/Y) * 100. Percentage change from A to B: ((B - A)/|A|) * 100, shown with the absolute change B - A.
Browser API or library: Pure JavaScript Number arithmetic; no external library.
Input limits: Any IEEE 754 double-precision float; effective range roughly ±1.8e308 with ~15 significant digits of precision.
Output: Numeric result displayed alongside the calculation formula, rounded to 4 decimal places and at most 15 significant digits (values below 0.0001 keep 4 significant figures, values of 10^15 or more use exponential notation). Copyable to clipboard.
Known limitations: When the divisor is zero (“X is what % of Y” with Y = 0, or “% change” from 0), the tool shows “Cannot divide by zero” and no percentage. Standard floating-point rounding applies to repeating decimals.

Frequently asked questions

How do you calculate a percentage of a number?: Divide the percentage by 100 and multiply by the number: 15% of 200 is (15 / 100) × 200 = 30. The calculator also finds what percent one number is of another and the percentage change between two values, and shows the formula under every result.
Is my data sent to a server?: All calculations run entirely in your browser using JavaScript. Our servers are not involved at any point.
Can I calculate VAT or sales tax?: Yes. Use the percentage of a number calculator, enter the pre-tax amount and the tax rate to get the tax amount, then add it to the original for the total.
How do I calculate a percentage decrease?: Use the percentage change calculator. If the new value is less than the original, the result will be negative, showing the percentage decrease.

Related tools

Background reading: Complete guide to calculator tools

Reviewed and tested September 30, 2026.