Percentage difference compares two values without treating either one as the original. Take the absolute difference, divide it by the average of the two values and multiply by 100. The difference between 150 and 180 is 30 ÷ 165 × 100 ≈ 18.18%, whichever value comes first.
Formula
% difference = |a − b| ÷ ((a + b) ÷ 2) × 100 Examples
- Two shops sell the same item for 45 and 55: 10 ÷ 50 × 100 = 20%.
- Two measurements, 9.6 and 10.0: 0.4 ÷ 9.8 × 100 ≈ 4.08%.
Common mistakes
- Using it when there is a clear before and after. Then use percentage change: 150 → 180 is +20%, not 18.18%.
- Using it with values of opposite sign: the average can be near 0 and the result explodes.
In Excel and Google Sheets
- Values in A2 and B2 (format as %)
=ABS(A2-B2)/AVERAGE(A2,B2)
FAQ
What is the difference between percentage difference and percentage change?
Percentage change has a direction (old to new) and divides by the old value. Percentage difference has no direction and divides by the average of the two.
Can the percentage difference be over 100%?
Yes, when one value is more than three times the other. For 10 and 50 it is about 133%.
Which one should I use to compare a measurement with a known value?
Percent error. Use percentage difference when both values are measurements of equal standing.
How we calculate: exact decimal math (no rounding errors), you choose the decimal places, and your numbers never leave your browser. Methodology →
Updated October 2026