In general, business property is depreciated under a midyear rule that allows half a year’s depreciation for the first year, whether you buy property in January or December. However, if you buy more than 40 percent of the business property you put into service for the year during the fourth quarter, the midquarter convention takes over. With it, you depreciate each piece of property as though it were placed into service in the middle of the calendar quarter in which it was purchased. You claim just six weeks’ worth of depreciation for property put in service during the final quarter, for example.