Compares two numbers relative to their average — a different, symmetric measure from percentage change, which is relative to a starting point. See both side by side to tell them apart.
Quick answers to the questions people ask most about percentage difference.
Percentage difference measures the gap between two numbers relative to their average, not relative to either number specifically. It's calculated as the absolute difference divided by the average of the two numbers, times 100.
Percentage change is directional and relative to a starting value — going from 80 to 100 is a +25% change, but going from 100 to 80 is a -20% change. Percentage difference is symmetric and relative to the average of both numbers, so it gives the same result either way: about 22.2% for 80 and 100, regardless of which one came first.
Because it divides by the average of the two numbers rather than by either number individually, swapping which number is "first" and which is "second" doesn't change the average, so the result stays the same. This makes it useful for comparing two values where neither one is naturally the "before" or "starting" figure.
Use percentage change when one number is clearly a starting point and the other is a result over time, like a price before and after a sale. Use percentage difference when you're comparing two independent measurements or estimates where neither one is the "original," like two lab results or two competing price quotes.