Percentage Difference Calculator

Percentage difference compares two peer values

Use percentage difference when neither value is a designated starting value or reference. The absolute difference is divided by the average of the two values, making the result symmetric: swapping the first and second values does not change it.

Example

For 80 and 100, the absolute difference is 20 and the average is 90. The percentage difference is 20 ÷ 90 × 100 = 22.22%.

Difference versus percentage change

Percentage change measures movement from an old value to a new one and divides by the old value. Percentage difference instead compares two measurements without choosing a baseline. If both values are zero, the percentage form is undefined because their average is zero.

Percentage difference is symmetric

Percentage difference compares two values without treating either one as the original baseline. It divides the absolute difference by the average of the two magnitudes, then multiplies by 100. Swapping the two inputs therefore produces the same result. This differs from percentage change, where the starting value is the denominator and direction matters.

If both values are zero, the percentage difference is undefined because the average denominator is zero, even though the absolute difference is zero. When values can be negative, explain whether the comparison uses magnitudes or signed business rules. For measurements, also report units and relevant uncertainty so a small numerical difference is not presented as meaningful without context.