X% of Y, what percent one number is of another, percentage change, and adding a percent
Estimates only, not financial advice. What you type stays on your device. Updated on 24 Oct 2026.A percentage of a number is the percentage divided by 100, times the number, so 25% of 80 is 0.25 × 80 = 20. A percentage change is the difference divided by the starting value, times 100, so going from 80 to 100 is a 25% increase.
Pick the question under Work out: X% of Y, X is what % of Y, % change from X to Y, Add or take off X% of Y, or Y is X% of what.
Type the two numbers in the X and Y boxes; a minus sign before X takes the percentage off.
Read the answer as a sentence, with each step of the working shown below it.
Press Share result to copy a link that opens the same question and numbers.
Most percentage questions are one of five, and each has its own formula. This page puts all five behind one switch, shows the answer as a plain sentence, and writes out every step so you can check it or copy the method for an exam.
The five questions.
| Question | Formula | Example |
|---|---|---|
| X% of Y | X ÷ 100 × Y | 25% of 80 = 20 |
| X is what % of Y | X ÷ Y × 100 | 30 is 37.5% of 80 |
| % change from X to Y | (Y − X) ÷ X × 100 | 80 to 100 = +25% |
| Add or take off X% of Y | Y × (1 + X ÷ 100) | 1,200 + 18% = 1,416 |
| Y is X% of what | Y ÷ (X ÷ 100) | 45 is 15% of 300 |
Percent and percentage points. A rate moving from 10% to 12% has risen by 2 percentage points, but by 20 percent of itself. The change mode gives the second figure; subtract the two rates yourself for the first.
Increases and decreases are not symmetrical. A price that rises from 80 to 100 goes up 25%, but falling back from 100 to 80 is a 20% drop, because each change is measured against a different starting value. The same is true of discounts in a row: 10% off and then another 10% off is 19% off in total, not 20%.
What it does not do. The calculator rounds what it shows to six decimal places, while working at full precision. It does not handle compound growth over several periods; use the compound interest or CAGR calculators for that. A change from zero has no percentage, and the page says so instead of showing infinity. For exam marks there is a dedicated marks percentage calculator.
Everything runs in your browser; nothing you type is sent anywhere.
Divide the percentage by 100 and multiply by the number. For 25% of 80, 25 divided by 100 is 0.25, and 0.25 times 80 is 20. Choose X% of Y on the calculator, type 25 and 80, and the working is shown step by step.
Divide the part by the whole and multiply by 100. For 30 out of 80, 30 divided by 80 is 0.375, so the answer is 37.5%. Choose X is what % of Y and type the part first, then the whole.
Subtract the old value from the new one, divide by the old value and multiply by 100. From 80 to 100 the difference is 20, and 20 divided by 80 is 0.25, a 25% increase. A negative answer is a decrease, and the page names it as one.
Each percentage is measured against its own starting value. Rising 25% from 80 gives 100, and falling 20% from 100 returns to 80, because 20% of the larger number equals 25% of the smaller one. Two changes in a row multiply rather than add.
Multiply the price by 1 plus the percentage divided by 100. A 1,200 price plus 18% tax is 1,200 times 1.18, which is 1,416. Choose Add or take off X% of Y; a minus sign before the percentage takes it off instead.
Divide the known amount by the percentage written as a decimal. If 45 is 15% of a total, 45 divided by 0.15 gives 300. Choose Y is X% of what, type 15 as X and 45 as Y, and the original number is shown with the working.
Formula only: no rates or limits are read from an official source.
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