Formula
% difference = |a − b| ÷ ((a + b) ÷ 2) × 100
- a, b — the two values
- (a + b) ÷ 2 — their average, used as the base
Divide the gap between the values by their average and multiply by 100.
Worked example
10 and 20
- First value
- 10
- Second value
- 20
Percentage difference
66.6667%
Absolute difference: 10
Average of the two values: 15
How it works
Percentage difference uses the average of the two values as the base, so swapping them changes nothing: 10 and 20 differ by 10, the average is 15, and 10 ÷ 15 × 100 = 66.67% either way round.
That is different from Percentage Change Calculator, where 10 → 20 is +100% but 20 → 10 is −50% because the starting point is different. Pick percentage difference when you are comparing two measurements, two quotes or two groups; pick percentage change when something moved over time.
Assumptions and limits
- If both values are zero (or they cancel to an average of zero) the percentage is undefined and the tool says so.
Related tools
Percentage Change CalculatorSigned percentage change from a starting value to a new value, up or down.Percentage Increase CalculatorFind the percentage increase between two values, or add a percentage to a number.Percentage Decrease CalculatorFind the percentage drop between two values, or take a percentage off a number.Percentage CalculatorFind X% of a number, what percent one number is of another, or the whole from a part.Average CalculatorMean, median, mode, range, sum and count for a list of numbers.Proportion CalculatorSolve for the missing value in direct or inverse proportion (A/B = C/D).