Percentage Calculator
Solve any percentage question in one place. Find what X% of a number is, what percent one number is of another, the change from an old value to a new one, or the difference between two peer 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 four 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 either directional change or the symmetric difference 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", "% change", or "% difference".
- Type your numbers into the two boxes — there is no order to memorize, each box is labeled for the mode you picked.
- For a change between rates, select "These inputs are percentages" to see the percentage-point movement as well as the relative change.
- 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. Copy the complete calculation when you need an auditable record.
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. The old value is the baseline; using its magnitude keeps direction meaningful even when it is negative.
- Percent difference: result = |A − B| ÷ ((|A| + |B|) ÷ 2) × 100. Neither value is the baseline, so swapping A and B does not change the answer.
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.
Change, difference, and percentage points
Use percent change when the values are ordered: an old baseline followed by a new value. Use percent difference when A and B are peers and neither is the reference; its average-based denominator makes the comparison symmetric. When both inputs are rates, there is one more useful reading. A move from 20% to 25% is a 25% relative increase, but the direct gap is 5 percentage points. The rate option shows both without treating them as interchangeable.
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.
- Peer comparison: values of 80 and 100 differ by |80 − 100| ÷ ((80 + 100) ÷ 2) × 100 = 22.2222%.
- Rates: moving from 20% to 25% is a 25% relative increase and a 5 percentage-point 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 four modes on a single screen, makes the baseline explicit, 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 compare a new value with an old baseline. Subtract old from new, divide by the magnitude of the old value, and multiply by 100. 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 directional change is not symmetric.
When should I use percent difference instead of percent change?
Use percent change when one value is the old baseline and the other is the new value. Use percent difference when the two values are peers and neither is the baseline. Percent difference divides the absolute gap by the average magnitude, so swapping Value A and Value B does not change the answer.
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.