when can i use the half year convention 
the half year convention can be used if the mid quarter convention does not apply the mid quarter convention applies if the aggregate basis of property placed in service during the last three months of your tax year exceeds 40 of the aggregate basis of all property placed in service during the tax year 2for example assume you bought a machine for 2 000 and placed it in service in january a desk for 500 in april and a computer for 2 000 in november the computer placed in service during the last three months of the year exceeds 40 of the total basis of all property acquired during the year 2 000 2 000 500 2 000 44 4 therefore all three assets must use the mid quarter convention 3