Percentage Calculator

You're in the middle of a sale, trying to figure out how much you'll save on that 20% off jacket. Or maybe you're looking at a stock's performance and need to know the percentage change from last month. Percentages are everywhere — in shopping, finance, statistics, and even when splitting a restaurant bill. Our free online Percentage Calculator handles all the common scenarios instantly, so you don't have to fumble with a calculator or second-guess your math. Just pick your mode, plug in your numbers, and get the answer in seconds.

How to Use the Percentage Calculator

Using this calculator is straightforward. Here's a step-by-step guide:

1. Select a calculation mode — Choose from the dropdown menu. You can find "What is X% of Y?", "Percentage change from X to Y", "Percentage difference between X and Y", or "X is Y% of what number?".
2. Enter your two values — The labels will change based on your selected mode. For example, if you choose "What is X% of Y?", you'll enter the percentage (X) and the total (Y).
3. Click "Calculate" — Your result appears instantly in the box below. For percentage change and difference modes, the result includes a % sign.
4. Use the Clear button to reset all fields and start a new calculation.
5. Open Advanced Options (the gear icon) to adjust decimal places (0–6) and choose your rounding mode: standard (half-up), ceiling (always up), or floor (always down).

Formula

The calculator uses four core formulas depending on the mode you select. Each one is built on basic arithmetic, but we'll break them down so you understand exactly what's happening.

What is X% of Y?
Formula: Result = (X ÷ 100) × Y
Example: What is 20% of 150? (20 ÷ 100) × 150 = 0.2 × 150 = 30.

Percentage change from X to Y
Formula: Change = ((Y - X) ÷ |X|) × 100
Example: If a stock was $50 (original) and is now $65 (new), the change is ((65 - 50) ÷ 50) × 100 = (15 ÷ 50) × 100 = 30%. A positive result means an increase.

Percentage difference between X and Y
Formula: Difference = (|X - Y| ÷ ((|X| + |Y|) ÷ 2)) × 100
Example: Value 1 is 80, Value 2 is 100. The average is (80 + 100) ÷ 2 = 90. The absolute difference is 20. So the difference is (20 ÷ 90) × 100 ≈ 22.22%.

X is Y% of what number?
Formula: Result = (X ÷ Y) × 100
Example: 30 is 20% of what number? (30 ÷ 20) × 100 = 1.5 × 100 = 150.

What is a Percentage Calculator?

A percentage calculator is a tool that automates common percentage math problems. Instead of manually applying formulas — which can be error-prone, especially when dealing with decimals or negative numbers — you simply choose the type of calculation you need and enter your values. The tool handles the rest, including rounding and formatting.

Percentages are a way of expressing a number as a fraction of 100. They're used everywhere: to calculate discounts, interest rates, probability, statistical differences, and growth rates. Anyone from students and teachers to business owners, investors, and shoppers can benefit from quick, accurate percentage calculations.

For instance, if you're comparing two products and want to know which one gives you a better percentage discount, or if you're tracking your monthly spending changes, this calculator saves time and mental effort. It's also great for checking your homework or verifying calculations at work.

Frequently Asked Questions

Why does the percentage difference formula use the average of the two values?

Using the average as the denominator makes the percentage difference symmetric — meaning the result is the same regardless of which value you label as first or second. This is different from percentage change, which is directional and depends on which value is the original. The average-based formula is standard for comparing two values without implying a "before" and "after."

Can I use negative numbers with this calculator?

Yes, the calculator accepts negative numbers for most modes. In the percentage change mode, the absolute value of the original number is used, which correctly handles decreases (resulting in a negative percentage). For percentage difference, absolute values are used, so the result is always positive. Just be aware that entering zero as an original value in percentage change mode will trigger an error, because division by zero isn't possible.

What rounding mode should I use for financial calculations?

For most everyday purposes, the standard "half-up" rounding is fine. But if you're dealing with financial transactions where rounding rules matter (like tax calculations or invoice totals), you may want to use "Ceiling" (always round up) or "Floor" (always round down) to match your accounting standards. The calculator's Advanced Options let you switch between them easily.