# Percentage calculator

> To find a percentage of a number, multiply the number by the rate and divide by 100. For example, 20% of 150 is 150 × 20 ÷ 100 = 30. The percentage calculator handles four jobs: X% of a value, what percent one number is of another, percent change between two values, and the final price after a discount or markup.

Source: https://www.calterix.com/en-us/calculator/percentage/ · Updated 11/06/2026 · en-US

## How to calculate a percentage

A percent is a fraction with a denominator of 100. Saying 20% means 20/100, or 0.20. Every percentage problem comes down to multiplying or dividing by 100.

```
X% of Y = Y × X ÷ 100
X is what percent of Y = X ÷ Y × 100
Percent change = (new − old) ÷ old × 100
```
Example: 20% of 150 = 150 × 20 ÷ 100 = 30.

### Discounts and markups

To take 15% off a $200 jacket, work out 200 × 15 ÷ 100 = $30 and subtract it: $170. To add a 10% markup to $1,000, add $100 and land on $1,100. The shortcut is to multiply by 0.85 for the discount and by 1.10 for the markup.

## Worked examples

| Question | Math | Answer |
| --- | --- | --- |
| 10% of 250 | 250 × 10 ÷ 100 | 25 |
| 15% of $80 | 80 × 15 ÷ 100 | $12 |
| 7.5% of 1,200 | 1,200 × 7.5 ÷ 100 | 90 |
| 30 is what percent of 150 | 30 ÷ 150 × 100 | 20% |
| From 80 to 100 | (100 − 80) ÷ 80 × 100 | +25% |
| From 100 to 80 | (80 − 100) ÷ 100 × 100 | -20% |

A 25% rise and a 20% drop are mirror images, but the base changes, so they are not the same percent.

Tipping 18% on a $64 dinner works the same way: 64 × 18 ÷ 100 = $11.52. For a ready-made version with bill splitting, use the [tip calculator](https://www.calterix.com/en-us/calculator/tip/). To add sales tax to a price, try the [sales tax calculator](https://www.calterix.com/en-us/calculator/sales-tax/).

## Common mistakes

- **Adding percentages in a row.** A 10% raise followed by a 10% cut does not bring you back to the start: 100 becomes 110, then 99.
- **Using the wrong base.** Percent change always divides by the starting value.
- **Mixing up percentage points and percent.** Going from 10% to 12% is a 2 percentage point jump, which is a 20% relative increase.

For other proportions, use the [proportion calculator](https://www.calterix.com/en-us/calculator/proportion/). To see how money grows over time, try the [compound interest calculator](https://www.calterix.com/en-us/calculator/compound-interest/).

## Frequently asked questions

### How do I calculate a percentage of a number?

Multiply the number by the percentage and divide by 100. For example, 20% of 150 is 150 × 20 ÷ 100 = 30.

### How do I find what percent one number is of another?

Divide the part by the total and multiply by 100. For 30 out of 150, that is 30 ÷ 150 × 100 = 20%.

### How do I calculate a discount?

Find the percentage of the price and subtract it. With 15% off a $200 item, the discount is $30 and the sale price is $170.

### How do I calculate percent increase?

Subtract the old value from the new one, divide by the old value, and multiply by 100. From 80 to 100, the increase is (100 − 80) ÷ 80 × 100 = 25%.

### How do I calculate percent decrease?

Use the same formula, and a negative answer means a drop. From 100 to 80, (80 − 100) ÷ 100 × 100 = -20%.

### How do I use the percent key on a regular calculator?

Type the amount, the operator, and the percentage. On the [scientific calculator](https://www.calterix.com/en-us/calculator/scientific/), 1000 + 10% gives 1,100.