Because the LAW says you must use the mid-month convention, which means a placed in service date of 1/1/18 gets a 1/2 month of depreciation.
As I said before, do it right and you will get 1/2 month of depreciation for January. There is nothing wrong with that. Don't be concerned that it is not a 'full' year, as the LAW says that is how it NEEDS to be. Just let the program do the correct calculation.
