Percentage Calculator — free, instant, in your browser
Three quick percentage calculations, with answers as you type.
This tool runs entirely in your browser. Your files are never uploaded — they stay on your device.
Percentages come up everywhere — discounts, tips, tax, grades, interest and growth rates. This calculator covers the three questions you actually ask: what is X% of a number, what percent one number is of another, and how much something changed from one value to the next.
Everything runs right here in your browser, so there is nothing to install and nothing to send anywhere. Type your numbers and the answer updates instantly.
How it works
Each mode is a single arithmetic formula, evaluated by JavaScript the moment you change a field. "X percent of Y" computes (X ÷ 100) × Y, so 15% of 80 returns 12. "X is what percent of Y" computes (X ÷ Y) × 100, so 24 out of 80 returns 30%. The increase-or-decrease mode computes ((new − old) ÷ old) × 100, so a change from 80 to 100 returns +25% and 100 down to 80 returns −20% — note that the two are not the same size, because the starting value is different in each direction.
There is no server, no API call and no round trip. The code is downloaded once with the page and then runs locally on your device, which is why results appear with no perceptible delay and why the numbers you enter never leave your browser. You can disconnect from the internet and the calculator keeps working.
When to use it
The three modes map onto the everyday questions people actually ask. Use "X percent of Y" for a sale price (how much is 30% off this?), a restaurant tip, sales tax or VAT, a commission, or a portion of a budget. Use "X is what percent of Y" to turn a raw score into a grade, to express one figure as a share of a total, or to work out what fraction of a goal you have reached. Use percentage increase or decrease for price changes, salary raises, year-over-year growth, weight or measurement changes, and before-and-after comparisons.
Because everything stays on your device, it is also a safe choice for sensitive figures — salary negotiations, medical measurements, private finances — that you would not want to type into a site that quietly uploads what you enter.
Tips
Direction matters with change: always put the earlier value as the original and the later value as the new one, or the sign of the answer will flip. Remember that a percentage rise and the fall that undoes it are different sizes; a 50% increase is reversed by a 33.3% decrease, not another 50%. To reverse a discount and find an original price, divide by the remaining fraction rather than multiplying — an item at 60 after 25% off was 60 ÷ 0.75 = 80, not 60 × 1.25. Finally, watch the difference between percent and percentage points: going from 10% to 12% is a two-percentage-point move but a 20% relative increase.
How to use Percentage Calculator
- Pick the calculation you need using the tabs above.
- Type your numbers into the two fields — the answer updates as you type.
- Read the result, including the plain-English explanation below it.
- Switch tabs any time to run a different kind of percentage calculation.
Frequently asked questions
How do I calculate X% of a number?
Divide the percentage by 100 and multiply by the number. For example, 20% of 150 is (20 ÷ 100) × 150 = 30. The first tab does this for you instantly.
How do I find what percent one number is of another?
Divide the first number by the second and multiply by 100. For example, 30 is (30 ÷ 150) × 100 = 20% of 150. Use the second tab for this.
How is percentage increase or decrease calculated?
Subtract the original value from the new value, divide by the original value, then multiply by 100. A move from 80 to 100 is a 25% increase; from 100 to 80 is a 20% decrease.
Are my numbers sent to a server?
No. This calculator is pure JavaScript that runs entirely in your browser. Nothing you type is uploaded, stored or seen by anyone else.