Use two numbers to solve common percent-of, percent-of-total, increase and decrease questions.
Percentage change, discounts, tax, tips and everyday percent-of-number questions.
Enter two values and the calculator returns several common percentage relationships at once: what percent the first number is of the second, the first number as a percentage applied to the second, and the second number after the first number is treated as a percentage increase or decrease.
| Question | Calculation | Answer |
|---|---|---|
| What is 20% of 150? | 0.20 × 150 | 30 |
| 30 is what percent of 120? | 30 ÷ 120 × 100 | 25% |
| Increase 80 by 15% | 80 × 1.15 | 92 |
| Decrease 200 by 25% | 200 × 0.75 | 150 |
If you know that a value is a certain percentage of an unknown total, divide the known value by the percentage written as a decimal. Example: if 45 is 30% of a number, the original number is 45 ÷ 0.30 = 150.
To find 18% of 250, calculate 18 ÷ 100 × 250 = 45. In the results, look for the line describing the first value as a percent of the second value. A separate line answers the different question “18 is what percent of 250?”: that is 7.2%.
Use the correct direction: “20% of 50” is 10, while “20 as a percent of 50” is 40%. Entering the same two values can answer multiple percentage questions; read each result label.
Multiply the number by 0.20. For example, 20% of 150 is 30.
Divide the part by the whole and multiply by 100.
Divide the known result by the percentage expressed as a decimal.
| Question | Formula |
|---|---|
| What is X% of Y? | (X ÷ 100) × Y |
| X is what percent of Y? | (X ÷ Y) × 100 |
| What is the percentage increase? | ((new − old) ÷ old) × 100 |
| What is the percentage decrease? | ((old − new) ÷ old) × 100 |
For discounts, sales tax and related percent problems, browse the Percentages, Discounts & Sales Tax topic hub.
See how formulas, sources and limitations are handled across ERICH Calculators.