liminfoPercentage Calculator
Free web tool: Percentage Calculator
About Percentage Calculator
The Percentage Calculator is a free online tool that handles the three most common percentage calculations: finding a percentage of a number (Y% of X), calculating the percentage change between two values (from old to new), and determining what percentage one number is of another (X is what % of Y). Switch between modes with tab buttons and enter your values — results update instantly in real time with up to 4 decimal places for precision.
Percentage calculations appear constantly in everyday life and professional work. Students solve percentage problems in math and science courses. Marketers calculate conversion rates, click-through rates, and year-over-year growth. Financial analysts compute profit margins, tax rates, and investment returns. Shoppers figure out discount amounts and tips. Data analysts determine proportions and distributions. This calculator eliminates manual formula setup by providing dedicated modes for each common scenario.
All calculations run entirely in your browser using standard JavaScript arithmetic. No data is sent to any server. The results display includes both the calculated value and a description label showing the formula context (e.g., "15% of 200" or "Change rate from 100 to 150"), so you can verify the calculation at a glance.
Key Features
- Three calculation modes: "Y% of X", "Percentage Change", and "X is what % of Y"
- Real-time results — values update instantly as you type, no submit button needed
- Up to 4 decimal places of precision for accurate financial and scientific calculations
- Clear formula description label showing the calculation context alongside the result
- Large, prominent result display for easy reading
- Mode switching resets inputs for clean calculations without leftover values
- 100% client-side processing — no data transmitted to any server
- Works with decimals and negative numbers for comprehensive percentage scenarios
Frequently Asked Questions
How do I calculate a percentage of a number?
Use the "Y% of X" mode (the default). Enter the number in the first field (X) and the percentage in the second field (Y%). The tool multiplies X by Y/100 and displays the result. For example, 15% of 200 = 200 × 15/100 = 30.
How do I calculate percentage change?
Switch to the "Change Rate" mode. Enter the previous (old) value and the new value. The tool calculates ((new - old) / |old|) × 100. A positive result means an increase, negative means a decrease. For example, changing from 200 to 250 gives +25%, while 200 to 150 gives -25%.
How do I find what percentage one number is of another?
Use the "X is what % of Y" mode. Enter the partial value (X) and the total value (Y). The tool calculates (X / Y) × 100. For example, 25 is 12.5% of 200, because 25/200 × 100 = 12.5%.
Can I use decimal numbers?
Yes. All three modes accept decimal numbers in both input fields. The result is displayed with up to 4 decimal places for precision. For example, you can calculate 7.5% of 133.33 or the percentage change from 99.9 to 100.1.
What happens if I divide by zero?
The tool handles division by zero gracefully. In Change Rate mode, if the previous value is 0, the result shows 0 rather than infinity. In "X is what % of Y" mode, if Y is 0, the result is also 0. This prevents confusing error displays while indicating that the calculation is not meaningful with a zero denominator.
Can I use negative numbers?
Yes. Negative numbers are supported in all modes. For percentage change, the tool uses the absolute value of the old number as the denominator, which correctly handles scenarios like changes from negative to positive values. The sign of the result correctly indicates the direction of change.
How precise are the results?
Results are rounded to 4 decimal places, which is sufficient for virtually all percentage calculations including financial analysis, scientific data, and statistical work. The tool uses JavaScript's native floating-point arithmetic (IEEE 754 double precision), providing approximately 15-17 significant digits of internal precision before rounding for display.
Is my data safe?
Yes. All calculations are performed in your browser using basic JavaScript arithmetic operations. No input values or results are transmitted to any server, stored in cookies, or logged anywhere. The tool is safe for calculations involving sensitive financial data, performance metrics, or business figures.