How to use the percentage calculator
- Find the box that matches your question.
- Type your numbers. Results update immediately, so there’s nothing to click.
- Read the answer and the formula underneath it to see how it was worked out.
The four percentage formulas
X% of Y: multiply Y by X and divide by 100. For example, 15% of 200 is 200 × 15 ÷ 100 = 30. This is how you work out tips, discounts, tax and commission.
X is what % of Y: divide X by Y and multiply by 100. If you scored 30 out of 120, that’s 30 ÷ 120 × 100 = 25%. The calculator warns you if Y is zero, because dividing by zero is undefined.
Percentage change: subtract the old value from the new one, divide by the absolute old value and multiply by 100. Going from 80 to 100 is a 25% increase, while going from 100 to 80 is a 20% decrease. Using the absolute value keeps the direction correct even for negative numbers, such as a loss shrinking from −50 to −25.
Increase or decrease by %: multiply the number by (1 + percent ÷ 100). Use a negative percentage to decrease: 250 reduced by 20% is 200.
Everyday examples
- Working out a 25% sale price or a 10% tip.
- Turning test scores into percentages.
- Comparing this month’s sales or traffic with last month’s.
- Adding tax or VAT to a price.
Percentage calculator FAQ
Why isn’t a 20% increase undone by a 20% decrease?
Because the second percentage is taken from a different base. 100 + 20% = 120, but 120 − 20% = 96. To return to 100 you need a 16.67% decrease.
What’s the difference between percent and percentage points?
Going from 10% to 12% is a rise of 2 percentage points, but a 20% increase in the rate itself.
How precise are the results?
Results show up to six decimal places, rounded for display.