Percentage Calculator
Three calculations in one ยท By Stuart Mathieson · Updated October 2026
Results
Result
How the percentage calculator works
"Percent" means "per hundred", so every percentage calculation moves between a part, a whole and a number out of 100. The calculator handles the three questions that come up most:
What is X% of Y?
Example: 15% of 240 = 0.15 × 240 = 36.
X is what percent of Y?
Example: 45 out of 180 = 45 ÷ 180 × 100 = 25%.
Percent change from X to Y
Example: going from 80 to 92 = (92 − 80) ÷ 80 × 100 = +15%. A negative result is a decrease.
Common percentage mistakes
- Increases and decreases aren't symmetric. Going from 80 to 92 is a 15% increase, but going back from 92 to 80 is a 13.04% decrease, because the starting value is different. A 50% rise followed by a 50% fall leaves you at 75% of where you started.
- Percent vs percentage points. If an interest rate rises from 4% to 5%, it has gone up by 1 percentage point - but that is a 25% increase in the rate.
- Working backwards. To find a price before a 20% increase such as sales tax, divide by 1.2 rather than taking 20% off: $120 ÷ 1.2 = $100, whereas $120 minus 20% is $96.
- Adding percentages. Two discounts of 10% don't make 20% off. The second applies to the already-reduced price, so the total is 1 − 0.9 × 0.9 = 19% off.
Fractions, decimals and percentages
| Fraction | Decimal | Percent |
|---|---|---|
| 1/2 | 0.5 | 50% |
| 1/3 | 0.333... | 33.3% |
| 1/4 | 0.25 | 25% |
| 1/5 | 0.2 | 20% |
| 1/8 | 0.125 | 12.5% |
| 1/10 | 0.1 | 10% |
| 3/4 | 0.75 | 75% |
Frequently asked questions
How do I find what percent one number is of another?
Divide the first number by the second and multiply by 100. Choose "X is what % of Y" mode, enter the two values, and the calculator does this for you.
How is percent change calculated?
Percent change is (new value - original value) divided by the absolute value of the original value, times 100. A positive result is an increase, a negative result is a decrease.
Why does percent change use the absolute value of the original number?
Using the absolute value keeps the sign of the result meaningful (increase vs. decrease) even when the original value is negative, which is the standard convention for percent change.
What's the difference between percent and percentage points?
Percentage points measure the simple difference between two percentages, while percent measures the relative change. A rate going from 4% to 5% has risen by 1 percentage point, which is a 25% increase.