That's the estimated range that depends on the current temperature, how the car was driven the past 18 miles, what driving mode is selected, your driving efficiency, and probably other dependencies that aren't so clear. However, the Idaho National Laboratory measured the battery pack capacity of 4 new 2014 i3's over as long as 15 months and 12k miles
. On all of the i3's, the battery pack capacity decreased at the rate of ~7.5% over 15 months and 12k miles.
The actual range of our 2014 i3 has decreased by ~15% after 5.5 years and 10k miles. Others have reported more or less actual, not estimated, range loss. It's difficult to measure actual range loss with any accuracy because of so many variables.
It's impossible to assess whether your estimated range is typical without knowing much more. In general, your estimated range has certainly been reported by other i3 owners, so this isn't an outlier.