Percentage Difference Calculator
Percentage difference = |first − second| ÷ ((first + second) ÷ 2) × 100. It measures the gap between two numbers as a percentage of their average.
Last updated 2026-08-14
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quizExample
How this calculator works, with real numbers (no JavaScript needed):
Inputs
- First value
- 80
- Second value
- 100
Results
- Percentage difference
- 22.2%
- Absolute difference
- 20
functionsThe formula
Percentage difference measures how far apart two numbers are, as a percentage of their average. Unlike percentage change, it treats both numbers symmetrically — the answer is the same whichever value you call first.
The formula
Percentage difference = |A − B| ÷ ((A + B) ÷ 2) × 100
The denominator is the average of the two numbers, so the result is a "relative to the middle" measure rather than relative to a fixed starting point.
Worked example
Compare 80 and 100:
Average = (80 + 100) ÷ 2 = 90
Difference = |80 − 100| = 20
Percentage difference = 20 ÷ 90 × 100 ≈ 22.2%
So 80 and 100 differ by about 22.2%. Reverse the order (100 vs 80) and you get the same answer — that's what makes it "difference" rather than "change".
Percentage difference vs percentage change
- Percentage change (80 → 100) is +25% — it's relative to the starting value, so it depends on direction.
- Percentage difference (80 vs 100) is 22.2% — symmetric, and it uses the average as the base.
Use change when one value is clearly the "before" and the other the "after". Use difference when comparing two independent values with no direction — two quotes, two prices, two measurements, two estimates.
Everyday uses
- Price comparison — is quote A really that different from quote B?
- Estimates vs actuals — how far off was the prediction?
- Survey and polling comparisons — two groups' agreement levels
- Laboratory and engineering measurements — tolerance between readings
helpFrequently asked questions
question_markHow do I calculate percentage difference?
Divide the absolute difference between the two numbers by their average, then multiply by 100: |A − B| ÷ ((A + B) ÷ 2) × 100.
question_markWhat is the percentage difference between 80 and 100?
|80 − 100| ÷ 90 × 100 ≈ 22.2%. The average of 80 and 100 is 90, and the difference of 20 is 22.2% of that average.
question_markWhat is the difference between percentage difference and percentage change?
Percentage change is relative to the starting value and has a direction (+25% from 80 to 100). Percentage difference is symmetric and relative to the average of the two values (22.2%).