Percentage Difference Calculator
Calculate the symmetric percent difference between any two values compared against their average.
Percentage difference
Percentage difference formula
When comparing two experimental readings, prices from two vendors, or independent measurements, use the symmetric percentage difference:
The denominator is the average of both numbers, ensuring the calculation produces identical results in either direction.
Worked examples with real numbers
Values 80 and 100
Difference: |80 − 100| = 20
Average: (80 + 100) ÷ 2 = 90
Ratio: 20 ÷ 90 = 0.2222...
22.22% difference
Values 10 and 20
Difference: |10 − 20| = 10
Average: (10 + 20) ÷ 2 = 15
Ratio: 10 ÷ 15 = 0.6666...
66.67% difference
Frequently asked questions
What is percentage difference?
Percentage difference is a symmetric comparison between two numbers relative to their arithmetic mean (average). Because neither number is an 'initial' or 'baseline' value, the result is identical regardless of which number is entered first.
What is the difference between percentage difference and percentage change?
Percentage change compares a final number against an earlier starting baseline: ((New − Old) ÷ |Old|) × 100. Percentage difference compares two values without direction or chronological order, dividing by their average: (|A − B| ÷ ((A + B) ÷ 2)) × 100.
Can percentage difference be negative?
No. Percentage difference is defined using absolute value |A − B|, so the result is always zero or positive.
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