Percentage Difference Calculator

Compare two values with no clear “before” or “after”, as a percentage of their average.

Value A	40
Value B	60

Value A

Value B

Percentage difference

40%

40 and 60 differ by 20, which is 40% of their average, 50.

Change from A to B: 50%
Change from B to A: -33.3333%

The two values and their average

A40
Average50
B60

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

About the Percentage Difference Calculator

Percentage difference is symmetrical: it gives the same answer whichever value comes first, because it divides by the average of the two. Use it to compare two prices, two measurements or two products. When one value is the starting point, use percentage change instead.

The formula

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

Worked example

40 and 60

Difference = 20, average = 50
20 ÷ 50 × 100 = 40%

Questions people ask

Why isn't it 50%?

50% is the change from 40 to 60. Percentage difference uses the average, 50, as the base.

When should I use percentage difference?

When neither value is the reference, for example comparing two shops' prices or two lab measurements.