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Percentage calculator
Four everyday percentage questions, answered as you type, each with the formula behind the result.
What is X% of Y?
Result
12
15% of 80 is 12
Multiply the number by the percentage, then divide by 100.
80 × 15 ÷ 100 = 12
X is what percent of Y?
Result
15%
12 is 15% of 80
Divide the part by the whole, then multiply by 100.
12 ÷ 80 × 100 = 15%
Percentage change from X to Y
Result
+15%
An increase of 15%
Subtract the old value from the new one, divide by the old value, then multiply by 100.
(92 − 80) ÷ 80 × 100 = 15%
Add or subtract a percentage
Result
92
80 plus 15% = 92
68
80 minus 15% = 68
To add, multiply by (1 + X ÷ 100). To subtract, multiply by (1 − X ÷ 100).
80 × (1 + 15 ÷ 100) = 92
80 × (1 − 15 ÷ 100) = 68
Everything is calculated on your device. Your entries are saved in this browser only, so they are here when you come back.
How percentages are calculated
“Percent” means “out of 100”, so 15% is 15 ÷ 100 = 0.15. Every percentage question is one of a few small formulas built on that.
- X% of Y: Y × X ÷ 100. Example: 15% of 80 = 80 × 15 ÷ 100 = 12.
- X is what percent of Y: X ÷ Y × 100. Example: 12 is 12 ÷ 80 × 100 = 15% of 80.
- Change from X to Y: (Y − X) ÷ X × 100. Example: from 80 to 92 is (92 − 80) ÷ 80 × 100 = a 15% increase.
- Add or subtract X%: Y × (1 + X ÷ 100) or Y × (1 − X ÷ 100). Example: 80 plus 15% is 92, and 80 minus 15% is 68.
Things that often trip people up
- Rises and falls are not symmetric. Going from 100 to 80 is a 20% decrease, but going back from 80 to 100 is a 25% increase, because the starting value changed.
- A change from 0 has no percentage. Any rise from zero would be infinitely large, so the calculator says so instead of showing a number.
- Percent and percentage points differ. If a rate moves from 10% to 12%, it rose by 2 percentage points, which is a 20% increase.
- Taking a discount off and then adding the same percent back does not return the original price: 100 minus 20% is 80, and 80 plus 20% is 96.
Tips
- Negative numbers and decimals work. You can type a comma or a point as the decimal mark.
- To find the price before tax or a markup, divide instead: a price of 115 including 15% is 115 ÷ 1.15 = 100.
- Use “Copy result” to paste the answer, with its numbers, into a message or a spreadsheet note.
FAQ
How do I calculate a percentage of a number?
Multiply the number by the percentage and divide by 100. For example, 15% of 80 is 80 × 15 ÷ 100 = 12.
How do I work out what percent one number is of another?
Divide the part by the whole and multiply by 100. For example, 12 out of 80 is 12 ÷ 80 × 100 = 15%.
How is percentage change calculated?
Subtract the old value from the new value, divide by the old value, then multiply by 100. A positive result is an increase and a negative one is a decrease.
Why can’t I get the percentage change from 0?
Because the formula divides by the starting value. Dividing by zero has no answer, so any rise from 0 cannot be written as a percentage.
How do I add 15% to a price?
Multiply the price by 1.15. For example, 80 plus 15% is 80 × 1.15 = 92. To take 15% off, multiply by 0.85 instead.
What is the difference between percent and percentage points?
Percentage points are the plain difference between two percentages. Going from 10% to 12% is a rise of 2 percentage points, but a 20% increase relative to the starting 10%.
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