Compare two values fairly, when neither one is the "original."
Percentage Difference
10.53%
A symmetric comparison — it doesn't matter which value you enter first.
Percentage difference is easy to confuse with percentage change, but they answer different questions. Percentage change assumes one value is the "before" and one is the "after" — like an old price and a new price. Percentage difference is for comparing two values that are simply different, with neither one being the starting point — like comparing two competitors' prices, or two lab measurements of the same thing.
Because there is no "original" value to divide by, percentage difference uses the average of the two numbers as the base instead, which keeps the comparison fair regardless of which number you list first.
Formula
Percentage Difference = (|A − B| ÷ ((A + B) ÷ 2)) × 100
The result is always positive, because it does not matter which value is "first."
Worked Example
Worked example
Why not just use percentage change here?
If you used percentage change and picked Product A as the "old" value, you would get a different number than if you picked Product B as the "old" value — that inconsistency is exactly what percentage difference avoids, since it treats both values symmetrically.
Common uses
Comparing prices across two stores, comparing two experimental measurements in a science lab, comparing two candidates' scores on the same test, or any comparison where "which one came first" genuinely does not apply.
Frequently Asked Questions
How is percentage difference different from percentage change?
Percentage change needs a defined "old" and "new" value and can be positive or negative. Percentage difference compares two values with no defined order and always gives a positive result.
Why does this formula use the average of the two numbers?
Using the average as the base keeps the result the same no matter which value you enter first, which is what makes it a fair, symmetric comparison.
When should I use this instead of percentage change?
Use percentage difference when comparing two independent values (like two prices or two measurements). Use percentage change when one value is clearly the "before" and the other is the "after."
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