The three percentage formulas you actually need
| Question | Formula | Example |
|---|---|---|
| What is X% of Y? | Y × X ÷ 100 | 20% of 150 = 30 |
| X is what % of Y? | X ÷ Y × 100 | 45 of 60 = 75% |
| Percent change from A to B | (B − A) ÷ A × 100 | 80 → 100 = +25% |
| Y increased by X% | Y × (1 + X ÷ 100) | 250 + 15% = 287.50 |
Percent increase vs. percentage points
If a savings rate goes from 4% to 5%, it rose by 1 percentage point, but that is a 25% increase in the rate itself. News stories and loan offers mix these up often, so check which one is meant.
Why a 50% drop needs a 100% gain to recover
Percent change is always measured from the starting value. A $100 item that falls 50% is $50. To get back to $100 from $50 it must rise by $50, which is 100% of the new, smaller starting value. The same logic explains why two discounts of 20% do not add up to 40% — see the discount calculator.
Want step-by-step examples for grades, tips, raises, and price changes? Read how to calculate percentages.
Percentage Calculator FAQs
How do I calculate a percentage of a number?
Multiply the number by the percentage and divide by 100. For example, 15% of 80 is 80 × 15 ÷ 100 = 12.
How do I find the percentage between two numbers?
Divide the part by the whole and multiply by 100. If you scored 42 out of 50, that is 42 ÷ 50 × 100 = 84%.
How do I calculate percent increase?
Subtract the old value from the new value, divide by the old value, and multiply by 100. From 80 to 100 is (100 − 80) ÷ 80 × 100 = 25%.
How do I take a percentage off a price?
Multiply the price by (1 − percent ÷ 100). 30% off $60 is 60 × 0.70 = $42.