How this calculator works
Percentage difference is symmetric: swapping A and B leaves the answer unchanged. It is useful for comparing two measurements on the same scale. It is not directional growth, percentage error against a known true value, or a change over time. Two zeros have no nonzero average, so that case is undefined.
The formula
Percentage difference = |A − B| / ((A + B) / 2) × 100.A quick example
Values of 100 and 120 differ by 20. Their average is 110, so percentage difference is approximately 18.18%. Percentage change from 100 to 120 would instead be 20%.
How to use this calculator
- Enter two non-negative values measured in the same units.
- Ensure at least one value is positive.
- Calculate the absolute difference and the percentage relative to their average.
A few common questions
Does swapping the inputs change the answer?
No. The absolute gap and average are unchanged.
Can one value be zero?
Yes. If exactly one value is zero, the percentage difference is 200%.
Why exclude negative values?
Opposing signs can make the average zero or misleading. This tool intentionally uses non-negative comparisons.