How to use this calculator
Use this when neither measurement is the baseline. Enter two nonnegative values, take their absolute difference, and divide by their average. This makes the comparison symmetric. If one number is an earlier baseline and the other a later result, use percentage change instead.
Formula
|First value − Second value| ÷ ((First value + Second value) ÷ 2) × 100
Worked example
For 80 and 100, the gap is 20 and the average is 90. Percentage difference = 20 ÷ 90 × 100 = 22.222222…%. Swapping the two values leaves the answer unchanged.
Assumptions and limitations
Both values must be nonnegative. Two zeros have an average of zero, so the percentage difference is undefined. One zero and one positive value gives 200%. Different fields may use another definition, such as percent error relative to a known reference.
Frequently asked questions
Why is this different from percentage change?
Difference uses the average of the two values as the denominator. Change uses the starting value. For 80 and 100 these are 22.222222…% difference and 25% change.
How precise are these results?
Calculations use ordinary floating-point arithmetic. Results show up to six decimal places; very small nonzero values use scientific notation. They are estimates for everyday arithmetic, not arbitrary-precision accounting.
Can I use decimals and negative numbers?
Yes where the input allows them. Percentage change requires a nonnegative starting value; difference uses nonnegative values; discount requires a nonnegative price and a rate between 0% and 100%.
Keep the same units for both values. Amounts have no assumed currency.