Percentage Calculator
Find X% of a number, what percent one number is of another, percentage change, percentage difference and percent increase.
Percentage formulas
"Percent" means "per hundred", so 15% is 15/100 or 0.15. Almost every percentage problem is one of the five types this calculator handles.
| Question | Formula | Example |
|---|---|---|
| What is A% of B? | A ÷ 100 × B | 15% of 240 = 36 |
| A is what % of B? | A ÷ B × 100 | 36 is 15% of 240 |
| % change from A to B | (B − A) ÷ |A| × 100 | 80 → 100 is +25% |
| % difference | |A − B| ÷ ((A + B) ÷ 2) × 100 | 80 vs 100 is 22.2% |
| Increase B by A% | B × (1 + A ÷ 100) | 240 + 15% = 276 |
Percentage change vs percentage difference
Use percentage change when there is a clear before and after, such as a price going from $80 to $100 (+25%). Going back from $100 to $80 is −20%, not −25%, because the starting point changed. Use percentage difference to compare two values with no natural order, like the prices at two stores. It divides by their average, so the answer is the same whichever way round you enter them.
Percentage points
When a rate itself changes, be careful with wording. If a mortgage rate goes from 4% to 5%, it has risen by one percentage point but by 25 percent. News reports often mix these up.
Quick mental tricks
- 10% of a number: move the decimal point one place left (10% of 240 = 24).
- 5% is half of 10%; 20% is double 10%; 1% moves the decimal two places.
- Percentages are reversible: 8% of 50 equals 50% of 8, which is 4.
Frequently asked questions
How do I calculate a percentage of a number?
Divide the percentage by 100 and multiply by the number. For example, 15% of 240 is 0.15 × 240 = 36.
How do I calculate percentage increase?
Subtract the old value from the new value, divide by the old value and multiply by 100. From 80 to 100: (100 − 80) ÷ 80 × 100 = 25%.
What is the difference between percent and percentage points?
Percentage points measure the simple difference between two percentages. A move from 10% to 12% is 2 percentage points, which is a 20% relative increase.
Last reviewed Oct 20, 2026. Results are estimates; check important decisions with a qualified professional.