Percentage calculator online
Work out percentages instantly: a percentage of an amount, what percentage one number is of another, and the change between two values.
A slide rule with two parallel scales of the same length, one behind the other, and a cursor that crosses both. In front, a box with a window showing the result. Enter, Space or the arrow keys move from one step to the next.
How to use it
- Choose the calculation you need.
- Type the two values, with a point for decimals; thousands separators such as 1,500 are fine.
- The result appears right away, with no button to press.
Frequently asked questions
How do you calculate a percentage of an amount?
Multiply the amount by the percentage and divide by 100. For example, 21% of 50 is 50 × 21 ÷ 100 = 10.5.
How do I work out a discount?
Calculate the percentage of the price and subtract it. A 30% discount on 80 is 24, so the final price is 56.
How is percentage change calculated?
Subtract the starting value from the final one, divide by the starting value and multiply by 100. From 40 to 50 the change is (50 − 40) ÷ 40 × 100 = 25%.
The percentage formulas
A percentage is a fraction of 100: 25% is 25 out of every 100, that is, a quarter. Almost every percentage problem comes down to three questions, and the calculator has a mode for each: how much a percentage of an amount is, what percentage one amount is of another, and how much a value has changed.
| What you want to know | Formula | Example |
|---|---|---|
| A percentage of an amount | amount × percentage ÷ 100 | 15% of 80 is 12 |
| One number as a percentage of another | part ÷ total × 100 | 30 out of 120 is 25% |
| The change between two values | (final − initial) ÷ initial × 100 | From 80 to 100 is a 25% rise |
| A price after a discount | price × (1 − discount ÷ 100) | 60 with 20% off is 48 |
| A price after an increase | price × (1 + increase ÷ 100) | 60 plus 20% is 72 |
Discounts, increases and common mistakes
To apply a discount you work out the percentage of the price and subtract it; for an increase, you add it. A shortcut: multiplying by 0.80 is the same as taking 20% off, and multiplying by 1.20, the same as adding it.
Going up 20% and then down 20% does not take you back to where you started: 100 becomes 120 and then 96, because the second percentage is calculated on a larger amount. For the same reason, two successive discounts of 20% and 10% do not add up to 30%, but to 28%.
Do not confuse percentages with percentage points either. If an interest rate goes from 2% to 3%, it has risen by one percentage point, but by 50% in relative terms.
