Percentage Difference Calculator

Use percentage difference when neither value is the “original” — for example comparing two shops, two measurements or two products.

Compare two values

Percentage difference40%
Percentage change from 40 to 60
50%
Percentage change from 60 to 40
−33.3333%

Working

  1. Absolute difference: |40 − 60| = 20
  2. Average of the two values: (40 + 60) ÷ 2 = 50
  3. Divide and multiply by 100: 20 ÷ 50 × 100 = 40%

Formula

Percentage difference divides the gap between two values by their average, so the answer is the same whichever value you put first.

difference % = |A − B| ÷ ((A + B) ÷ 2) × 100

|A − B|
the absolute difference (always positive)
(A + B) ÷ 2
the average of the two values

Worked example

Compare 40 and 60

  1. Absolute difference: |40 − 60| = 20
  2. Average: (40 + 60) ÷ 2 = 50
  3. 20 ÷ 50 × 100 = 40%

The percentage difference is 40%.

Notice how this differs from percentage change: 40 → 60 is a 50% increase, while 60 → 40 is a 33.33% decrease. The percentage difference of 40% sits between them and does not depend on direction.

Which measure should I use?

SituationUse
A value changed over time (old → new)Percentage change
Two measurements of equal statusPercentage difference
A measurement against a known or accepted valuePercentage error: |measured − true| ÷ true × 100

Limitations

If A and B have opposite signs or their average is zero, the percentage difference is not meaningful (and is undefined when the average is zero). For data that can be negative, compare the absolute difference instead.