Percentage Calculator
Work out what X% of a number is, and what one number is as a percent of another.
Results update as you type.
About this calculator
A percentage calculator handles the three everyday percentage questions in one place: what is X percent of a value, what percent one number is of another, and the percentage change between two numbers. Pick the question from the dropdown and fill in the two boxes — the tool applies the matching formula automatically.
The maths behind each is simple. "X% of Y" multiplies Y by X and divides by 100, so 15% of 200 is 200 × 15 ÷ 100 = 30. "X is what % of Y" divides X by Y and multiplies by 100, so 30 out of 200 is 15%. "% change from X to Y" takes the difference over the original, so 200 rising to 260 is (260 − 200) ÷ 200 × 100 = 30%.
Use it for discounts and tips, tax, test scores, tip splitting, commission, growth rates and any of the countless moments daily life throws a percentage at you. Because it accepts decimals and negative numbers, it also works for shrinkage, losses and before-and-after comparisons.
Frequently asked questions
How do I find a percentage of a number?
Multiply the number by the percent and divide by 100. For example 15% of 200 is 200 × 15 ÷ 100 = 30.
How does the percentage change mode work?
Choose "% change from X to Y", enter the starting number as X and the ending number as Y, and the calculator returns the percent difference between them. Going from 50 to 80 gives (80−50)/50 × 100 = a 60% increase.
How do I turn a percentage into a decimal?
Divide the percentage by 100, or move the decimal point two places to the left. 15% becomes 0.15 and 7.5% becomes 0.075. To go the other way, multiply the decimal by 100.
What percent is one number of another?
Divide the part by the whole and multiply by 100. If 30 of 200 questions are correct, that is 30 ÷ 200 × 100 = 15%. Choose the "X is what % of Y?" mode to do this directly.
How do I add or subtract a percentage from a number?
To add, multiply by (1 + percent ÷ 100); to subtract, multiply by (1 − percent ÷ 100). Adding 15% to 200 gives 200 × 1.15 = 230, and taking 15% off gives 200 × 0.85 = 170.
What does a negative percentage change mean?
It means the value fell. If the new value is smaller than the original, the change formula returns a negative percent — for instance 260 down to 200 is about −23%.
API — use this calculator from code
Call this calculator as a free JSON endpoint — no key required. Send the field values below as query parameters or JSON. Read the full API docs →
Endpoint
GET https://calculator.free/api/v1/percentage/curl
curl "https://calculator.free/api/v1/percentage/?mode=of&a=15&b=200"JavaScript fetch()
const r = await fetch(
"https://calculator.free/api/v1/percentage/?" + new URLSearchParams({
"mode": "of",
"a": "15",
"b": "200"
}));
const data = await r.json();
console.log(data.results);Results are estimates for general guidance only, not financial, medical or tax advice.