Percentage Calculator
Solve any percentage question in one place. Find what X% of a number is, what percent one number is of another, or the percent increase or decrease between two values. Pick the question you need, type your numbers, and the answer appears instantly. Everything runs in your browser, so your numbers never leave the page.
What is the Percentage Calculator?
The Percentage Calculator is a free, browser-based tool that answers the three percentage questions people run into every day. It works out what X% of a number is, tells you what percent one number is of another, and measures the percent increase or decrease between two values. Instead of remembering which formula to use, you pick the question you actually have and read off the answer.
How to use it
- Choose the mode that matches your question: "% of a number", "X is what % of Y", or "% change".
- Type your numbers into the two boxes — there is no order to memorize, each box is labeled for the mode you picked.
- Read the result below the inputs. There is no Calculate button and no page reload, so you can tweak a value and watch the answer update right away. Get your number and get on with your day.
The formula behind it
Each mode uses one plain formula:
- Percent of a number: result = (percent ÷ 100) × number. So 15% of 200 is 0.15 × 200 = 30.
- X is what percent of Y: result = (X ÷ Y) × 100. So 45 of 60 is (45 ÷ 60) × 100 = 75%.
- Percent change (increase or decrease): result = ((new − old) ÷ old) × 100. A positive answer is an increase, a negative answer is a decrease.
The tool shows the worked formula next to each result, so you can see exactly how the number was reached rather than trusting a black box.
Examples
- Tip on a bill: 18% of a $54 dinner → 0.18 × 54 = $9.72.
- Test score: scored 38 out of 50 → (38 ÷ 50) × 100 = 76%.
- Price change: a stock moves from $120 to $138 → ((138 − 120) ÷ 120) × 100 = 15% increase.
Common use cases
Shoppers use it to confirm a sale price or sales tax. Students and teachers use it to turn raw marks into grade percentages. Anyone splitting a bill checks a tip or a service charge. Investors and analysts measure how much a price, revenue, or metric grew or fell. It is also handy for quick everyday math — figuring out commission, interest, or how far you are toward a goal.
Why use this one
Most percentage pages only do one thing, so you bounce between tabs. This one puts all three modes on a single screen, updates live as you type, runs entirely in your browser (your numbers never leave your device), and needs no sign-up. You also see the formula behind every answer, which makes it useful for learning, not just for getting a number. When your question is more specific, try our Discount Calculator, Tip Calculator, or Loan Calculator.
Frequently asked questions
How do I calculate what percent one number is of another?
Divide the part by the whole and multiply by 100. For example, 45 out of 60 is (45 / 60) x 100 = 75%. In this tool, choose the 'X is what percent of Y' mode, enter 45 and 60, and the answer appears instantly.
How do I find a percentage of a number, like 15% of 200?
Convert the percentage to a decimal by dividing by 100, then multiply by the number: 15% becomes 0.15, and 0.15 x 200 = 30. In the 'percent of a number' mode you simply type 15 and 200 and read off 30.
What is the difference between percentage increase and percentage decrease?
Both measure how much a value changed relative to where it started. The formula is the same — (new value minus old value) divided by the old value, times 100 — but a positive result is an increase and a negative result is a decrease. Going from 80 to 100 is a 25% increase; going from 100 to 80 is a 20% decrease, which is why the two are not symmetric.
Is my data sent anywhere when I use this percentage calculator?
No. Every calculation runs locally in your browser with JavaScript. Nothing you type is uploaded to or stored on any server, so the numbers you enter stay private on your device.
Why does the result update without a Calculate button?
The tool recalculates on every keystroke, so the answer is always in sync with what you have typed. This makes it faster for quick checks — you can adjust a number and immediately see the new result without clicking or reloading the page.