Percent Difference: worked example
| First value | 80 |
|---|---|
| Second value | 100 |
| Percent difference | 22.2% |
| Absolute difference | 20 |
Percent Difference: formula
Enter the two values you want to compare. The percent difference divides the absolute difference by the average of the two, so neither value is treated as the reference. Use it when the numbers are equal in status, such as two measurements or two prices from different stores, not when one is the starting point of a change.
The values should be in the same units and both positive.
Percent Difference: changing First value
| First value | Percent difference | Absolute difference |
|---|---|---|
| 64 | 43.9% | 36 |
| 72 | 32.6% | 28 |
| 80 (example) | 22.2% | 20 |
| 88 | 12.8% | 12 |
| 96 | 4.1% | 4 |
Percent Difference: compare input ranges
| Input | Tested from | To | Percent difference: low input | Percent difference: high input | Swing |
|---|---|---|---|---|---|
| Second value | 90 | 110 | 11.8% | 31.6% | 19.8% (89%) |
| First value | 72 | 88 | 32.6% | 12.8% | 19.8% (89%) |
Percent Difference: individual input comparisons
| Input | Value | Percent difference | Absolute difference |
|---|---|---|---|
| First value | 64 | 43.9% | 36 |
| 72 | 32.6% | 28 | |
| 80 | 22.2% | 20 | |
| 88 | 12.8% | 12 | |
| 96 | 4.1% | 4 | |
| Second value | 80 | 0.000% | 0 |
| 90 | 11.8% | 10 | |
| 100 | 22.2% | 20 | |
| 110 | 31.6% | 30 | |
| 120 | 40.0% | 40 |
Percent Difference: combined input changes
| First value / Second value | 80 | 100 | 120 |
|---|---|---|---|
| 64 | 22.2% | 43.9% | 60.9% |
| 72 | 10.5% | 32.6% | 50.0% |
| 80 | 0.000% | 22.2% | 40.0% |
| 88 | 9.5% | 12.8% | 30.8% |
| 96 | 18.2% | 4.1% | 22.2% |
Percent Difference: which assumptions move the result?
Percent Difference: values and definitions
| Quantity and definition | Value used |
|---|---|
| First value | 80 |
| Second value | 100 |
| Percent difference | 22.2% |
| Absolute difference | 20 |
Percent Difference: half and double Second value
| Second value | Percent difference |
|---|---|
| 50 | 46.2% |
| 100 | 22.2% |
| 200 | 85.7% |
Common error: Using percent difference for a before-and-after change. It treats both values as equals, so it understates a rise and overstates a fall.
It is unsuitable when there is a clear before and after, where percentage change is more informative. If one value is zero, the percent difference is 200%, which is not very meaningful. Different fields use slightly different definitions.
It does not indicate which value is larger.
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Percent difference compares two values when neither one is the starting point. The gap is divided by the average of the two, so 80 against 100 is a difference of 20, or about 22.2 percent of their midpoint of 90. Percent change would say 25 percent, dividing by 80.
The two measures answer different questions, and swapping them gives different numbers.
Percentage change uses an earlier value as its base; percentage difference treats the two values symmetrically. If it did, you want percent change from that starting value, not percent difference.
Measure a change from a start on the percentage change calculator, and against an accepted value on the percent error page. The percentage and proportion calculators help with related comparisons. The mean and median page gives the average used in the denominator.
How is percent difference calculated?
Divide the absolute difference between two values by their average and multiply by 100, so 80 and 100 differ by 22.2% of their midpoint.
When should I use percent difference instead of percentage change?
When neither number is the starting point, such as comparing two measurements or two products, so the comparison should not favor one.
Why is percent difference symmetric?
Because it divides by the average of the two values, so swapping them does not change the result.