Work out a percentage of a number, what percent one number is of another, the percentage change between two values, a value increased or decreased by a percentage, the whole from a part, and the percentage difference between two numbers.
How to calculate a percentage
- Find the line that matches your question, for example “What is 15% of 200?”.
- Type your numbers into that line.
- Read the answer on the right. Each line works independently.
Percentage formulas
| Question | Formula | Example |
|---|---|---|
| X% of Y | Y × X ÷ 100 | 15% of 200 = 30 |
| X is what % of Y | X ÷ Y × 100 | 30 of 200 = 15% |
| % change | (new − old) ÷ old × 100 | 200 → 250 = +25% |
| Increase by X% | Y × (1 + X ÷ 100) | 1000 + 18% = 1180 |
| Decrease by X% | Y × (1 − X ÷ 100) | 1000 − 25% = 750 |
Percentage change vs percentage difference
Percentage change compares a new value with an original one, so direction matters: 200 to 250 is +25%, but 250 to 200 is −20%. Percentage difference compares two values without a “before” and “after”, dividing by their average, so the order does not matter.
Percentage points
When a rate moves from 10% to 12%, it rose by 2 percentage points, which is a 20% increase. News reports often mix these up.
Frequently asked questions
How do I calculate 20% of a number?
Multiply the number by 0.2. For example, 20% of 450 is 450 × 0.2 = 90.
How do I add 18% GST or sales tax to a price?
Use the “Increase by” line: increase by 18% of the price. Or use the Sales Tax Calculator, which also removes tax from a total.
Why is a 50% drop followed by a 50% rise not back to the start?
The rise is calculated on a smaller number: 100 → 50 → 75. Percentages compound.
Updated October 2026 · Built and tested by Sharjeel Tahir · How our tools are tested