Percentage Calculator
Find a percentage of a number, work out what percent one value is of another, and calculate percentage change.
About the Percentage Calculator
The Percentage Calculator handles the three percentage questions that come up most often in everyday life, work, and study — all in one place. Pick a calculation from the dropdown and the answer updates the moment you finish typing. Whether you're splitting a bill, checking a discount, grading a test, or tracking how much a price went up, this tool does the arithmetic for you and spells out the result in a plain sentence so there's no second-guessing.
The three modes cover the questions people actually ask. "What is X% of Y?" finds a portion of a total — perfect for tips, sales tax, discounts, and commissions. "X is what percent of Y?" turns a raw comparison into a percentage — useful for test scores, survey results, or how much of a budget you've spent. "Percentage change from A to B" measures growth or shrinkage between two numbers and tells you whether it's an increase or a decrease, which is exactly what you need for price changes, weight loss, salary raises, or investment returns.
Everything runs entirely in your browser. Nothing you type is sent anywhere, there's no sign-up, and once the page has loaded the calculator keeps working even without an internet connection. Empty or invalid entries simply show a friendly prompt instead of a confusing "NaN", and divide-by-zero cases are caught and explained rather than crashing the result.
How to use
- Choose a calculation from the dropdown at the top: percent of a number, what-percent, or percentage change.
- Enter your two numbers in the labelled boxes. The labels change to match the mode, so you always know which value goes where.
- Read the result in the highlighted box below — it appears instantly and is written as a full sentence, for example "15% of 200 = 30".
- Switch modes anytime without losing your numbers; each mode remembers its own inputs, so you can jump back and forth freely.
You can type decimals and negative numbers too. The result keeps enough significant figures to stay accurate without cluttering the screen, and very large or very small answers are shown in scientific notation so they remain readable.
Frequently asked questions
How do I calculate a percentage of a number?
Use the "What is X% of Y?" mode. Enter the percentage as X and the total as Y, and the tool computes Y multiplied by X divided by 100. For example, 15% of 200 is (200 × 15) ÷ 100 = 30. This is the calculation you want for tips, discounts, and sales tax.
How do I find what percent one number is of another?
Choose the "X is what percent of Y?" mode. Enter the part as X and the whole as Y; the result is (X ÷ Y) × 100. For instance, 30 out of 200 is (30 ÷ 200) × 100 = 15%. It's ideal for test scores, progress bars, and figuring out how much of a total something represents.
How is percentage change calculated, and what does the direction mean?
The "Percentage change from A to B" mode uses (B − A) ÷ A × 100, where A is the original value and B is the new one. A positive result is an increase and a negative result is a decrease — the tool labels the direction for you and shows the size of the change as a positive number, so "200 to 230" reads as a 15% increase.
What happens if I leave a box empty or type something invalid?
Nothing breaks. Instead of showing "NaN" or a wrong number, the calculator displays a short prompt asking you to enter both values. Only complete, valid numbers produce a result, so you'll never see confusing output.
Why do some calculations say the value can't be zero?
For "X is what percent of Y?" the total Y can't be zero, because dividing by zero is undefined — you can't take a percentage of nothing. Likewise, percentage change needs a non-zero starting value A, since there's no meaningful percent change from zero. The tool detects these cases and explains them instead of erroring.
Is my data private, and does this work offline?
Yes on both counts. Every calculation happens locally in your browser — no numbers are uploaded, stored, or tracked. After the page loads once, the calculator continues to work with no internet connection at all.