Percentage Difference (and How It Differs From Change)
What percentage difference means, its formula, and how it differs from percentage change — with worked examples.
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Frequently asked questions
What is the percentage difference formula?
Percentage difference = |a − b| ÷ ((a + b) ÷ 2) × 100. The gap between the values is divided by their average.
How is percentage difference different from percentage change?
Percentage change measures a move from an old value to a new one and divides by the old value. Percentage difference compares two values with no baseline and divides by their average, so it is symmetric.
When should I use percentage difference?
Use it when neither value is a starting point — for example comparing two independent measurements or two prices — rather than tracking growth over time.
Percentage Difference (and How It Differs From Change)
Percentage difference compares two values when neither one is the obvious “starting” point — for example two measurements, two prices in different shops, or two lab readings.
The percentage difference formula
Percentage difference = |a − b| ÷ ((a + b) ÷ 2) × 100. You divide the size of the gap by the average of the two values, so the order of a and b does not matter.
| Values | Calculation | Result |
|---|---|---|
| 40 and 60 | |40 − 60| ÷ 50 × 100 | 40% |
| 90 and 100 | |90 − 100| ÷ 95 × 100 | 10.5% |
Difference vs change
Use percentage change when one value comes before the other in time (old → new). Use percentage difference when the two values are simply being compared and neither is a baseline. Change divides by the starting value; difference divides by the average.
Why it is symmetric
Because the base is the average of the two numbers, comparing 40 to 60 gives the same percentage difference as comparing 60 to 40 — unlike percentage change, which depends on which value you start from.
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