How to use the percentage calculator
Each card answers one question. Type your numbers into the boxes; the answer and the formula update as you type. Decimals work with a point, for example 12.5.
- Percentage of a number: 15 % of 200 is 30. Useful for tips, discounts and commission.
- What percent is it: 30 out of 200 is 15 %. Useful for test scores and shares of a budget.
- Find the whole: if 30 is 15 %, the whole is 200. Useful when you know a discount but not the original price.
- Percentage change: from 80 to 100 is an increase of 25 %.
- Add or subtract: 200 plus 20 % is 240, minus 20 % is 160. Useful for sales tax and markdowns.
The formulas
| Question | Formula | Example |
|---|---|---|
| p % of W | W × p ÷ 100 | 200 × 15 ÷ 100 = 30 |
| A is what % of W | A ÷ W × 100 | 30 ÷ 200 × 100 = 15 % |
| A is p % of what | A × 100 ÷ p | 30 × 100 ÷ 15 = 200 |
| Change from A to B | (B − A) ÷ A × 100 | (100 − 80) ÷ 80 × 100 = 25 % |
| W plus / minus p % | W × (1 ± p ÷ 100) | 200 × 1.2 = 240 |
Two common mistakes
Up and down are not symmetric. A price that rises 25 % from 80 to 100 only has to fall 20 % to get back to 80, because the second change starts from the larger number.
Percent versus percentage points. If an interest rate goes from 4 % to 5 %, it rose by one percentage point, but by 25 percent. The calculator's change card gives you the second figure.
Frequently asked questions
How do I remove sales tax from a price?
Use the “Find the whole” card with the total price and 100 plus the tax rate. For $108 with 8 % tax, enter 108 is 108 % of what: the price before tax is $100.
Can I enter negative numbers?
Yes. The change card also works for negative starting values and measures the change relative to the size of the starting value.
Why does a 50 % discount followed by a 50 % increase not bring me back to the start?
100 minus 50 % is 50, and 50 plus 50 % is only 75. Each percentage is taken of a different base.
Is the calculator free?
Yes, free and without sign-up. Everything is calculated in your browser.