Percentage Difference Calculator
The percentage difference between 40 and 60 is 40%, because the 20-point gap is measured against their average of 50. This percentage difference calculator compares two values of equal standing, like two prices, two test scores, or two lab measurements. Unlike percentage change, the order you enter the numbers makes no difference to the result.
Quick answer
Percentage difference compares two values against their average, not against one of them.
Percentage difference
40%
Absolute difference
20
Average
50
What this tells you
- •Percentage difference compares two values against their average, not against one of them.
- •The formula is |a - b| / ((a + b) / 2) x 100.
- •It is symmetric. Comparing 40 to 60 gives the same answer as 60 to 40.
- •Use it when neither value is the natural starting point. When one clearly comes first, use percentage change instead.
How to Use
- 1Enter the first value.
- 2Enter the second value.
- 3Read the percentage difference, with the raw gap and the average shown below.
- 4Both values must be positive numbers of the same kind, like two prices in the same currency.
How It Works
Formula
percentage difference = |a - b| / ((a + b) / 2) x 100Take the absolute gap between the two values, divide by their average, and multiply by 100. For 40 and 60 the gap is 20 and the average is 50, so the difference is 40%. Dividing by the average rather than one of the values is what makes the measure symmetric and fair to both numbers.
Calculation note: values are processed in the order shown above, using the current input units.
Worked Examples
Two quotes for the same job
The $20 gap divided by the $50 average gives 0.40.
Two stores price an item at $95 and $105
The $10 gap against the $100 average is exactly 10%.
Lab measurements of 4.8 and 5.2
The 0.4 gap divided by the 5.0 average gives 8%, a common check in physics labs.
Percentage Difference Examples
Pairs of values and their percentage difference, always measured against the average.
| Value A | Value B | Difference |
|---|---|---|
| 40 | 60 | 40% |
| 95 | 105 | 10% |
| 50 | 100 | 66.67% |
| 20 | 25 | 22.22% |
| 80 | 80 | 0% |
| 10 | 30 | 100% |
Common mistakes
- Using percentage difference when you mean percentage change. If one value is the before and the other the after, divide by the before value, not the average.
- Dividing by one of the two values. The denominator is the average of both, which is why 50 vs 100 is a 66.67% difference and not 50% or 100%.
- Comparing values in different units. Both numbers must measure the same thing on the same scale for the result to mean anything.