NumberUtils

Percentage Difference Calculator

Enter two values to find the symmetric percentage difference between them — how far apart they are, as a percentage of their average.

Result

40%

Percentage difference = |a − b| ÷ ((a + b) ÷ 2) × 100

How it works

The absolute difference between the two values is divided by their average, then multiplied by 100. Neither value is treated as the "original", so entering them in the opposite order gives the same result.

For example, to compare 50 and 25: the difference is 25, the average is (50 + 25) ÷ 2 = 37.5, so the percentage difference is (25 ÷ 37.5) × 100 = 66.67%, rounded to 2 decimal places.

This symmetric calculation is different from the directional one used by the Percentage Change Calculator. Going from 25 to 50 is a 100% increase and going from 50 to 25 is a 50% decrease, but the percentage difference between 25 and 50 is 66.67% whichever way round they are entered. Use the difference when neither value is the starting point, such as two quotes or two measurements, and the change when one value came before the other.

Formula: Percentage difference = |a − b| ÷ ((a + b) ÷ 2) × 100

Examples

Two measurements

8 and 12 differ by 4, which is 40% of their average of 10.

One value much smaller than the other

50 and 25 differ by 25, which is 66.67% of their average of 37.5, rounded to 2 decimal places.

Values close together with decimals

5.50 and 6.00 differ by 0.50, which is 8.70% of their average of 5.75, rounded to 2 decimal places.

Common uses

  • Comparing two product prices to see how much they differ relative to their average.
  • Checking the variation between two repeated measurements in a test or experiment.
  • Assessing the gap between two quoted figures before making a decision.
  • Comparing two performance results to see the relative spread between them.

Things to keep in mind

  • Percentage difference is symmetric and always zero or positive — unlike percentage change, it does not say which value increased or decreased relative to the other. See the Percentage Change Calculator when direction matters.
  • Both values must be zero or more. Percentage difference compares the size of two quantities, which is not a meaningful comparison for a negative quantity, so negative input is rejected rather than producing a sign-dependent result.
  • The two values cannot both be zero, since their average would be zero and there would be nothing to express the difference as a percentage of.

Frequently asked questions

How is percentage difference different from percentage change?

Percentage difference is symmetric: it compares two values without treating either as the starting point, so swapping them gives the same answer. Percentage change is directional and depends on which value you call the original.

Why can I not enter a negative value?

Percentage difference compares the size of two quantities, such as two measurements or two prices. That comparison is not meaningful for a negative quantity, so the calculator asks for values of zero or more.

Background and method

  • Percentages The five everyday percentage calculations, percentage points versus percent, successive changes, and why reversing a percentage is not the same as applying it backwards.
  • Methodology: Percentages The exact rules, input limits and rounding this calculator follows.
Percentage Change Calculator Find the percentage change between an original value and a new value. Percentage Calculator Find a percentage of a number, work out percentage change, or reverse a percentage back to its original value.