What is X% of a number
Commission, tip, tax, or any share of a total.
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.
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% |
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. To add sales tax to a price, try the sales tax calculator.
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. To see how money grows over time, try the compound interest calculator.
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, 1000 + 10% gives 1,100.
Sources and method
Standard public-domain formulas. Every calculation is checked against independent numeric tests before it goes live.