04
Percentage difference
Compare two values when neither one is the starting point or baseline.
Formula: absolute difference ÷ average of the two absolute values × 100.
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Percentage Difference Calculator
When neither number is the "starting point" — two competing prices, two test scores, two cities' rents — percentage difference compares them fairly. It uses the average of both values as the reference, so the answer is the same whichever you enter first.
How the percentage difference calculator works
When neither number is the "starting point" — two competing prices, two test scores, two cities' rents — percentage difference compares them fairly. It uses the average of both values as the reference, so the answer is the same whichever you enter first.
The formula
|a − b| ÷ ((|a| + |b|) ÷ 2) × 100
Worked example
Two laptops cost $800 and $950. The absolute difference is $150. Their average is $875. Divide 150 by 875 and multiply by 100: about 17.14% difference.
Where this comes in handy
- Shopping: compare two similar products' prices without favoring either.
- Experiments: quantify how far apart two measurement runs are.
- Sports: compare two athletes' times or scores symmetrically.
- Quotes: see how much two contractor bids really differ.
Percentage Difference Calculator — frequently asked questions
When should I use percentage difference instead of percentage change?
Use percentage difference when there is no "before" and "after" — just two values to compare. Use percentage change when one value is clearly the starting point.
Why does the order of the numbers not matter here?
The formula divides by the average of both values, making it symmetric. Swapping a and b gives the identical answer, unlike percentage change.
What does a 0% difference mean?
The two values are equal. The larger the percentage, the further apart the values are relative to their size.
Can percentage difference exceed 100%?
Yes, when one value is much larger than the other. If a is tiny and b is huge, the difference approaches 200% as a approaches zero.
Is this the same as percent error?
They are related but not identical. Percent error compares a measured value against a known true value; percentage difference treats both values equally with no "correct" one.