How it works
Percent difference compares two values when neither one is the obvious starting point, such as two measurements of the same thing or the prices at two stores.
Instead of dividing by one value, it divides the absolute difference by the average of the two, so the answer is the same whichever order you enter them. Use percent change instead when there is a clear before and after.
Formula
percent difference = |A − B| ÷ ((A + B) ÷ 2) × 100
Questions people ask
Is percent difference the same as percent change?
No. Percent change divides by the original value and has a direction. Percent difference divides by the average and is always positive. For 10 and 20, percent change is 100% (10 to 20) but percent difference is 66.67%.
Can percent difference exceed 100%?
Yes, up to 200% for positive values. It reaches 200% when one value is zero and the other is not.
When is percent error used instead?
Percent error compares a measured value to a known true value: |measured − true| ÷ |true| × 100. Use it when one value is the accepted reference.