1. What does this tool do
This free online percentage calculator answers three common questions in one place: what is X% of a number, what percent is X of Y, and what is the percent change between two values. Use it for discount calculator, tip calculator, or percent change in grades, growth, or sales. Free, instant, and private—everything runs in your browser with no sign-up. Ideal for shopping discounts, tips, grades, or before/after comparisons.
2. How to use it
Quick start: Choose your calculation type (X% of Y, X is what % of Y, or percent change), enter the two values, and read the result. Copy or use it for your next step.
- Choose the calculation type — Select “X% of Y”, “X is what % of Y”, or “Percent change (X to Y)”.
- Enter values — Fill in the two fields according to the labels (e.g. percentage and number, or first and second value for change).
- Read the result — The answer appears as you type. Copy or use it for your next step.
3. How it works
Standard percent formulas: (1) X% of Y = (X/100) × Y; (2) X is what % of Y = (X/Y) × 100; (3) Percent change from X to Y = ((Y − X) / X) × 100. All calculations run client-side in your browser; no data is sent to any server.
4. Use cases & examples
- Discount calculator — Find 20% of $45, or the final price after a percent off.
- Tip calculator — Calculate 15% or 18% of a bill.
- Grades or scores — See what percent you got (e.g. 42 out of 50).
- Growth or decline — Percent change from last month to this month.
Example
- 25% of 80 → 20
- 15 is what % of 60 → 25%
- Percent change from 50 to 75 → 50%
5. Limitations & known constraints
- Numbers only — Enter numeric values; currency symbols or text are not parsed.
- Precision — Results use normal floating-point precision; very long decimals may be rounded for display.
- Division by zero — If the second value is 0 where it would divide, the tool will show an error or invalid result.