How to use the percentage calculator
- Find the sentence that matches your question, for example What is 15% of 200?
- Replace the numbers with your own. The answer updates as you type.
- Choose how many decimals you want in the Decimals box, or leave it on Auto.
Type numbers with a point for decimals. Commas and spaces in large numbers, such as 1,250, are accepted.
Percentage formulas
| Question | Formula | Example |
|---|---|---|
| What is X% of Y? | X / 100 x Y | 15% of 200 = 30 |
| X is what percent of Y? | X / Y x 100 | 30 of 200 = 15% |
| X is Y% of what number? | X / (Y / 100) | 30 is 15% of 200 |
| Percentage change from X to Y | (Y - X) / X x 100 | 50 to 75 = +50% |
| Increase X by Y% | X x (1 + Y / 100) | 200 + 15% = 230 |
| Decrease X by Y% | X x (1 - Y / 100) | 200 - 15% = 170 |
| Percentage difference | |X - Y| / ((X + Y) / 2) x 100 | 80 and 120 = 40% |
Percentage change, percentage difference and percentage points
- Percentage change compares a new value with an old one. The old value is the base, so the order matters: going from 50 to 75 is +50%, and going from 75 to 50 is -33.3%.
- Percentage difference compares two values that have no order, such as two prices or two measurements. It divides by their average, so the answer is the same both ways.
- Percentage points are the plain difference between two percentages. If a rate goes from 10% to 12%, it rises by 2 percentage points, which is a 20% increase.
For a starting value that is negative, the change is worked out against its absolute value. If the starting value is zero, a percentage change cannot be calculated.
Common mistakes
- Using the wrong base. Percentages are always a share of something. Check which number is the whole.
- Undoing a percentage with the same percentage. 100 increased by 20% is 120, but 120 decreased by 20% is 96, not 100. To get back, decrease by 16.67%.
- Adding percentages of different bases. A 10% rise followed by a 10% rise is 21% in total, not 20%.
Quick ways to work out a percentage
- 10% of a number: move the decimal point one place to the left.
- 5% is half of 10%, and 1% is the number divided by 100.
- 15% is 10% plus 5%. 20% is double 10%.
- 25% is a quarter, 50% is half and 75% is three quarters.
Discounts, tax and prices
To find a sale price, the percentage off, the original price before a discount or the price with tax, use the percent off calculator. It also handles stacked discounts.
More percentage calculators
For one calculation with more detail, open percentage of a number, percentage increase, percentage decrease, percentage change or percentage difference. The guide to percentage change has worked examples, spreadsheet formulas and code. To count the days between two dates, use days between dates.