Percentage Difference Calculator
Compare two values fairly: the percentage difference treats both values equally, using their average as the base.
About this tool
Percentage difference answers a different question from percent change. Percent change needs a “before” and an “after”; percentage difference is for comparing two values where neither is the original — two measurements, two quotes, two experimental results. It divides the absolute difference by the average of the two values, so swapping A and B gives the same answer.
Scientists and engineers use it to report agreement between measurements (and its cousin, percent error, when one value is the accepted truth). If one of your values is genuinely the starting point, use the percent change calculator instead — the results differ, and picking the right one is most of the battle.
How to use it
- Enter the first value in A.
- Enter the second value in B — order does not matter.
- Read the percentage difference: 0% means the values are identical.
Frequently asked questions
What is the formula for percentage difference?
|A − B| ÷ ((|A| + |B|) ÷ 2) × 100 — the absolute difference divided by the average of the two values' magnitudes, times 100.
Percentage difference vs percent change — which should I use?
Use percent change when one value came first (price then, price now). Use percentage difference when comparing two peers (two measurements, two offers) with no natural starting point.
Why can the difference reach 200%?
Because the base is the average of the two magnitudes, 200% is the largest result possible — it is reached when one value is zero, or when the two values are equal in size but opposite in sign (like −10 and 10).
What does a 0% difference mean?
The two values are exactly equal.