Percentage Difference Calculator
Enter two values to get the percentage difference between them, the same in either order, plus the percent change each way for comparison.
Free, no sign-upRuns in your browserHow we calculate
- Absolute difference
- 20
- Average of the two
- 90
- % change 80 → 100
- +25%
- % change 100 → 80
- −20%
How this was calculated
- Difference: |80 − 100| = 20
- Average: (80 + 100) ÷ 2 = 90
- Percentage difference: 20 ÷ 90 × 100 = 22.2222%
How percentage difference is calculated
Percentage difference compares two numbers when neither one is the "original". Take the absolute difference |A − B|, divide it by the average of the two values, (A + B) ÷ 2, and multiply by 100. Because the average does not depend on the order, the answer is the same whichever number you enter first. This percentage difference calculator shows each step, plus the two percent changes for comparison.
Worked example: 80 and 100
The difference is |80 − 100| = 20. The average is (80 + 100) ÷ 2 = 90. So the percentage difference is 20 ÷ 90 × 100 = 22.22%. Now compare with percent change: going from 80 to 100 is +25% (20 ÷ 80), but going from 100 to 80 is −20% (20 ÷ 100). Neither equals 22.22%, because they measure against a starting value instead of the average.
Percentage difference vs percentage change
Use percentage change when there is a before and an after: a price that rose, a score that fell. Use percentage difference when the two values are peers: two stores' prices for the same item, a measured value and a lab reference, the heights of two people. If you are unsure, ask whether swapping the numbers should change the answer. If it should not, use percentage difference.
Common mistakes
- Dividing by one of the numbers. That gives percent change, not percentage difference.
- Forgetting to average. The denominator is the mean of the two values, not their sum.
- Using it with a zero reference. Comparing 0 with 10 gives 200%, the maximum, which is technically right but rarely useful.
When the result is misleading
If the two numbers have opposite signs, the average of their absolute values is used and the percentage says little; compare the values directly. Percentages also hide scale: a 50% difference between 2 and 3 is tiny in absolute terms. For other percent questions, such as a percent of a number or a percent increase, use the percentage calculator.
Frequently asked questions
What is the percentage difference formula?
|A − B| ÷ ((|A| + |B|) ÷ 2) × 100. Divide the absolute difference by the average of the two values, then multiply by 100.
What is the percentage difference between 80 and 100?
22.22%. The difference is 20, the average is 90, and 20 ÷ 90 × 100 = 22.22%.
What is the difference between percentage difference and percentage change?
Percentage change measures from a starting value: 80 to 100 is +25%. Percentage difference compares two values with no starting point, using their average, so 80 and 100 differ by 22.22% in either order.
Can a percentage difference be over 100%?
Yes. 10 and 100 differ by 90 against an average of 55, which is 163.6%. The maximum for two positive numbers is 200%.
When should I use percentage difference?
When neither number is the original: comparing two prices, two measurements or two groups. If one value is clearly the before and the other the after, use percentage change.