Percentage Calculator
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Five percentage questions in one place, each answered the moment you type. What a percentage of a number is, what percent one number is of another, what number a percentage came from, the percent change between two numbers, and increasing or decreasing a number by a percentage.
The four percentage formulas
What is X% of Y: Result = X ÷ 100 × Y
X is what percent of Y: Result = X ÷ Y × 100
Percent change from X to Y: Result = (Y − X) ÷ |X| × 100
Increase or decrease Y by X%: Result = Y × (1 ± X ÷ 100)
A positive percent change is an increase, a negative one is a decrease. The starting value (X) in the percent change formula must not be zero, since a change from zero is not expressible as a percentage.
Worked examples
| Question | Numbers | Result |
|---|---|---|
| What is 15% of 200? | 15 ÷ 100 × 200 | 30 |
| 30 is what percent of 200? | 30 ÷ 200 × 100 | 15% |
| Percent change from 200 to 230 | (230 − 200) ÷ 200 × 100 | +15% |
| Increase 200 by 15% | 200 × 1.15 | 230 |
A common mistake: reversing percent change
A price that rises 20% and then falls 20% does not return to the start. $100 up 20% is $120. $120 down 20% is $96, not $100, because the second 20% is taken from a larger base. The percent change mode always measures against the value you enter as Value 1, so check which number is the starting point before reading the result.
For a fixed-price GST or sales tax calculation rather than a general percentage, use the GST calculator, which handles adding and removing tax at a set rate.
Frequently asked questions
How do I calculate a percentage of a number?
Divide the percentage by 100 and multiply by the number. 15% of 200 is 15 ÷ 100 × 200 = 30. Choose the first mode above and enter 15 and 200 to get the same result with the working shown.
How do I find what percent one number is of another?
Divide the first number by the second and multiply by 100. 30 out of 200 is 30 ÷ 200 × 100 = 15%. This is the calculation behind test scores, discounts and completion rates.
What is the formula for percentage change?
(New value − Old value) ÷ Old value × 100. A result above zero is an increase, below zero is a decrease. Using the absolute value of the old value in the denominator keeps the sign meaningful even when the old value is negative.
Why doesn't a 20% increase followed by a 20% decrease cancel out?
Because each percentage is taken from a different base. The increase is calculated on the original number, and the decrease is calculated on the larger, already-increased number, so the second change removes more than the first one added.
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This calculator is for general information and education only. It is not professional advice. Confirm important decisions with a qualified adviser.