The percent difference formula
Percent difference = |A − B| ÷ ((A + B) ÷ 2) × 100
Because it divides by the average of the two numbers, the result does not depend on which value you call A or B.
Worked example
Two stores sell the same headphones for $48 and $60.
- Difference: |48 − 60| = 12
- Average: (48 + 60) ÷ 2 = 54
- Percent difference: 12 ÷ 54 × 100 ≈ 22.22%
Compare that with percent change: going from $48 to $60 is a 25% increase, but going from $60 to $48 is a 20% decrease. Percent difference sits between the two and is the same in both directions.
Which percentage should I use?
| Situation | Use |
|---|
| Two measurements, prices or results of equal standing | Percent difference |
| A value that grew or shrank over time | Percent change |
| A measurement compared with an accepted true value | Percent error |
| A part of a whole | Percentage |
Last reviewed October 2026.
Frequently asked questions
What is percent difference?
Percent difference compares two values when neither one is the "original" or "correct" value. It divides the absolute difference by the average of the two values and multiplies by 100.
Is percent difference the same as percent change?
No. Percent change measures growth from an old value to a new value, so the order matters and the answer can be negative. Percent difference treats both values equally, so swapping them gives the same answer and it is always positive.
Can percent difference be more than 100%?
Yes, up to a maximum of 200%, which happens when one value is zero. For example, 0 and 10 have a difference of 10 and an average of 5, so the percent difference is 200%.
When should I use percent error instead?
Use percent error when one value is known to be correct, such as an accepted constant in a science lab. Use percent difference when comparing two measurements or two prices of equal standing.
What if the two values have opposite signs?
Percent difference is not meaningful when one value is negative and the other positive, because their average can be zero or tiny. Compare the absolute difference instead.