Percentage Difference Calculator
Compare two values symmetrically as a percentage of their average.
Result
How we calculated this
Formula
|First − Second| ÷ ((First + Second) ÷ 2) × 100
Using your values
Worked example
80 and 100 are 22.22% apart: |100 − 80| ÷ ((100 + 80) ÷ 2) × 100 = 20 ÷ 90 × 100 ≈ 22.22.
How it works
This tool compares two values symmetrically: neither is treated as a starting point or an original figure, so swapping the two values gives exactly the same result. It divides the absolute difference between them by their average, then expresses that as a percentage. If you actually have a before-and-after pair and want to know how much a value moved from its original figure, use the Percentage Change Calculator instead. Its result depends on which value is the original, and this one's does not. This tool accepts zero and positive values only: two values that sum to zero, including both being zero, have no defined average to compare against, and a negative value has no standard percentage-difference meaning, so both are shown as an error rather than an infinite or unreliable result.
A result written as a plain number is exact. A result starting with “≈” has been rounded to 10 significant figures, because its exact decimal never ends or is too long to read comfortably. When an exact value is long, its full digits are shown underneath. The calculation itself is never rounded: only the display is.
What this result means
The result is how far apart the two values are, as a percentage of their average, not as a percentage of either value on its own.
Method
|A − B| ÷ ((A + B) ÷ 2) × 100
Neither value is treated as a starting point or baseline; both are compared symmetrically against their shared average.
Common mistakes
- Confusing this with Percentage Change: that tool answers "how much did a value move from its original figure?" and needs a genuine before/after pair. This one answers "how far apart are these two figures?" and treats them as equals.
Assumptions and limitations
- Accepts zero and positive values only: a negative value has no standard percentage-difference meaning and is rejected, matching the established calculator sites this tool was checked against.
- Two values that sum to zero (including both being zero) have no defined average to compare against and are rejected rather than shown as infinite.