Three different questions
| Question | Formula | Example |
|---|---|---|
| What percent is A of B? | A ÷ B × 100 | 30 of 120: 30 ÷ 120 × 100 = 25% |
| What is the percent change from A to B? | (B − A) ÷ A × 100 | 50 to 65: 15 ÷ 50 × 100 = 30% increase |
| What is the percent difference between A and B? | |A − B| ÷ ((A + B) ÷ 2) × 100 | 50 and 65: 15 ÷ 57.5 × 100 = 26.1% |
What percent is one number of another?
Put the part on top and the whole on the bottom, divide, then multiply by 100. On a test, 42 right out of 50 is 42 ÷ 50 = 0.84, so 84%.
Percent change: which number goes on the bottom?
Always divide by the starting number. A price that goes from $80 to $100 rose 20 ÷ 80 = 25%. Going back from $100 to $80 is a 20 ÷ 100 = 20% fall, not 25%, because the starting number changed.
Finding the whole from a percentage
If 15 is 20% of a number, the number is 15 ÷ 0.20 = 75.
Do it with a calculator
The percentage calculator handles all of these, and the percentage increase calculator shows the change between two numbers. For test scores, use the test grade calculator.
Every worked example on this page was checked with Calcist's own engine and an independent reference.