orbitHow to use the percentage calculator
Choose the question you want to answer, type two numbers and read the result. It updates as you type and you can copy it with one click. Decimal numbers and negative values are supported.
The three calculations and their formulas
1. What is X% of Y?
Multiply the number by the percentage and divide by 100: X × Y ÷ 100. Example: 20% of 150 = 20 × 150 ÷ 100 = 30. Use it for tips, taxes, commissions and discounts.
2. X is what percent of Y?
Divide the part by the whole and multiply by 100: X ÷ Y × 100. Example: 30 out of 150 = 30 ÷ 150 × 100 = 20%. Use it for test scores, budget shares and completion rates.
3. Percentage change from X to Y
Subtract the old value from the new one, divide by the old value and multiply by 100: (Y − X) ÷ |X| × 100. Example: a price that rises from 80 to 100 has increased by (100 − 80) ÷ 80 × 100 = 25%. Falling from 100 to 80 is a decrease of 20% — not 25%, because the starting value is different.
Common mistakes with percentages
- Adding percentage changes. A 10% rise followed by a 10% fall does not bring you back to the start: 100 → 110 → 99.
- Percent versus percentage points. An interest rate going from 2% to 3% rose by one percentage point, but by 50% in relative terms.
- Using the wrong base. Always divide by the original value when calculating change.
Frequently asked questions
How do I add a percentage to a number?
Calculate the percentage with the first mode and add it, or multiply directly: to add 19% VAT to 50, compute 50 × 1.19 = 59.50.
How do I find the price before a discount?
Divide the sale price by (1 − discount ÷ 100). A jacket that costs 60 after 25% off originally cost 60 ÷ 0.75 = 80. For discounts, also try the Discount calculator.