Percentage calculator
Math & numbersHow much is that in per cent?
Percent of a number, what percent one number is of another, percentage change and difference, and the number before a discount.
What you enter stays on your device while you use this tool. Opening a shared link sends the settings in its address to HowToolbox to prepare the page.
Answer
20
10% of 200 is 20.
How it was worked out
- Formula
- 20 ÷ 100 × 150 = 30
- 150 plus 20%
- 180
- 150 minus 20%
- 120
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Percent of a number, what percent one number is of another, percentage change and difference, and the number before a discount.
How to use
- Choose what to calculate: a percent of a number, what percent one number is of another, a change, a difference, the whole from a part, or the value before a change.
- Enter the numbers. The answer and its formula update as you type.
- Copy the answer, or copy the link to share the same calculation.
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How it works
Per cent means “out of a hundred”: 20% is 20/100, or 0.2. So 20% of 150 is 20 ÷ 100 × 150 = 30, and 30 is 30 ÷ 150 × 100 = 20% of 150. Working backwards, if 30 is 20% of a number, the number is 30 ÷ 20 × 100 = 150.
A percentage change compares a new value B with an old value A: (B − A) ÷ |A| × 100. From 3 to 4 is an increase of 33⅓%, but from 4 back to 3 is a decrease of 25%, because each change is measured against its own starting point. A change from zero has no percentage.
When neither value is the starting point, the percentage difference measures the gap against their average: |A − B| ÷ ((|A| + |B|) ÷ 2) × 100. 100 and 120 differ by 20 ÷ 110 × 100 ≈ 18.18%, whichever way round you enter them. Other definitions exist (some divide by the larger value), so say which one you used.
A price after a 20% discount is 80% of the original, so the original is the price ÷ 80 × 100. Adding back 20% of the reduced price does not get you there. A change in a rate, such as 3% to 4%, is 1 percentage point but a 33⅓% increase. Formulas follow Wikipedia’s “Relative change” article.
Frequently asked questions
How do I find a percentage of a number?
Divide the percentage by 100 and multiply by the number. 15% of 80 is 0.15 × 80 = 12.
Why isn’t a 20% rise undone by a 20% fall?
Each percentage is taken of a different number. 100 plus 20% is 120, and 20% of 120 is 24, so a 20% fall leaves 96.
How do I find the price before a discount?
Divide the sale price by what remains after the discount. €80 after 20% off was €80 ÷ 0.8 = €100.
What is the difference between percentage change and percentage difference?
A change has a direction, from an old value to a new one, and is measured against the old value. A difference has no direction and is measured against the average of the two.
What is a percentage point?
The plain difference between two percentages. An interest rate going from 3% to 4% rises by 1 percentage point, which is a 33⅓% increase in the rate.
What percent is one number of another?
Divide the part by the whole and multiply by 100: 30 out of 250 is 30 ÷ 250 × 100 = 12%.
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