Updated June 17, 2026
Try the Percentage Calculator
Instant answers for any percentage problem: find the percent, the part, or the whole in one click.
A percentage is a part of 100. To find what percent one number is of another, divide the part by the whole and multiply by 100: (Part / Whole) x 100 = Percentage. So 15 out of 60 is (15/60) x 100 = 25%.
The three percentage problem types
| What you want | Formula | Example |
|---|---|---|
| Percent of a number | Whole x (% / 100) | 20% of 80 = 80 x 0.20 = 16 |
| What percent is A of B | (A / B) x 100 | 18 is what % of 72? = (18/72) x 100 = 25% |
| Find the whole | Part / (% / 100) | 30 is 40% of what? = 30 / 0.40 = 75 |
Quick mental tricks
10%: move the decimal one place left (10% of 340 is 34). 20%: find 10% and double it (68). 15%: find 10%, add half of that (34 + 17 = 51). Those cover most tips, discounts and quick tax checks without paper.
Worked examples
Example 1: 20% of 70. Multiply 70 by 0.20 = 14. Example 2: 15% of 50. Find 10% of 50 (5), add half (2.50) = 7.50. Example 3: 20% of a total where you only know a subtotal. If $18 is 20% of the total, the total is 18 / 0.20 = $90.
Percentage change
To find how much something changed as a percent: ((New - Old) / Old) x 100. If a price rises from $50 to $60, the change is ((60 - 50) / 50) x 100 = 20% increase. If it drops from $60 to $50, it is a 16.7% decrease.
Common uses
Percentages appear in discounts, tips, tax rates, grades and data comparisons. The formula is the same in all cases. Only which piece you are solving for changes. Use the Discount Calculator for sale prices or the calculator above to solve any of the three types in seconds. See also how to calculate a discount for a practical walkthrough.
Try the Percentage Calculator
Instant answers for any percentage problem: find the percent, the part, or the whole in one click.