Percentage Calculator
Calculate X% of Y, what percent X is of Y, or percentage change — instantly.
What is Percentage Calculator?
A percentage calculator is a tool that solves the three most common percentage calculations in everyday and business math: finding a percentage of a number, finding what percentage one number is of another, and calculating the percentage change between two values. Percentage change is computed as the difference between the new and original values divided by the original value, then multiplied by one hundred, where a positive result indicates growth and a negative result indicates decline. These calculations come up when working out discounts, taxes, tips, markups, interest, and comparing figures over time, and they are easy to get wrong by hand because the formula differs for each case. The calculator applies the correct formula behind the scenes and shows the result instantly as you type, while flagging undefined cases such as a divide-by-zero base. It also handles values above one hundred percent and negative numbers, which are valid in real-world change calculations.
How to Use Percentage Calculator
- Pick the calculation you need: "X% of Y", "X is what % of Y", or "% change from X to Y".
- Type the two numbers — the result updates instantly as you type.
- For percentage change, a positive result means an increase and a negative result means a decrease.
- Switch tabs any time without losing what you've typed in each one.
Examples
X% of Y
Input: 25% of 200
Output: 50
X is what % of Y
Input: 50 is what % of 200
Output: 25%
% change
Input: from 50 to 75
Output: +50%
Common Mistakes
- Confusing "X% of Y" with "X is what % of Y" — the first answers "what's 25% of 200?" (50), the second answers "50 is what percent of 200?" (25%). They're inverses of each other, easy to mix up.
- Reading a percentage-change result without checking the sign — a −20% result is a decrease, not an increase of 20%.
- Assuming percentage change is symmetric — going up 50% then down 50% does NOT return you to the original value (100 → 150 → 75, not back to 100).
Why Use This Tool
- Three common percentage calculations in one tool, each on its own tab so your numbers don't get mixed up.
- Instant results as you type, no "Calculate" button to click.
- Clear error messages instead of showing Infinity or NaN for divide-by-zero cases.
- Works with negative numbers and percentages over 100%.