Percentage Difference Calculator
Calculate the percentage difference between two numbers when neither is the obvious reference value.
What is the Percentage Difference Calculator?
Percentage difference compares two values symmetrically, dividing their absolute difference by their average. Use percentage change instead when one value is clearly the “before”.
How does it work?
The absolute difference is divided by the mean of the two values and multiplied by 100.
Formula
% difference = |A − B| ÷ ((A + B) ÷ 2) × 100
Example
Between 120 and 150, the difference is 30 and the average is 135, so the percentage difference is 22.22%.
Percentage difference vs percentage change
Percentage change measures movement from a starting value: from 80 to 100 is a 25% increase, and from 100 to 80 is a 20% decrease. The answer depends on which value comes first.
Percentage difference compares two values as equals. It divides the gap by the average of the two, so the answer is the same in either order. Between 80 and 100 the difference is 20, the average is 90, and the percentage difference is 22.22%.
| Values | Percentage difference | Change from first to second |
|---|
| 80 and 100 | 22.22% | +25% |
| 100 and 80 | 22.22% | −20% |
| 120 and 150 | 22.22% | +25% |
| 45 and 54 | 18.18% | +20% |
| ₹25,000 and ₹32,000 | 24.56% | +28% |
When to use which
- Percentage difference: comparing two shops’ prices, two lab measurements, two survey results or two quotes, where neither is the reference.
- Percentage change: comparing before and after, such as last year’s salary and this year’s, or yesterday’s price and today’s.
- Percentage error: comparing a measured value with a known correct value, dividing by the correct value.
Step by step
For 187 and 272: the difference is 85, the average is 229.5, and 85 ÷ 229.5 × 100 = 37.04%.
- Subtract one value from the other and ignore the sign.
- Add the two values and divide by 2 to get their average.
- Divide the difference by the average and multiply by 100.
Example: comparing two quotes
Two contractors quote ₹1,80,000 and ₹2,10,000 for the same work. The gap is ₹30,000 and the average quote is ₹1,95,000, so the quotes differ by 15.38%. Saying the second is “16.7% more expensive” or the first is “14.3% cheaper” is also correct, but each of those picks one quote as the reference; percentage difference avoids taking sides.
Things to keep in mind
The result can never exceed 200%, because the difference between two positive numbers can be at most twice their average. Very large percentage differences usually mean you should report the actual values or a ratio instead.
The formula is not meaningful when the values have opposite signs or when their average is zero. In those cases, report the absolute difference.
Frequently asked questions
Why does the order of values not matter?
Because the formula uses the average of both values as the reference, the result is the same either way.
Why does my answer differ from another website?
Many sites calculate percentage change and call it percentage difference. If the result changes when you swap the values, it is a percentage change, not a percentage difference.
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