Rates are set by fiscal year, effective October 1 each year. Find current rates in the continental United States ("CONUS Rates").
There are also depreciation tables associated with each of these conventions. Which one you use depends on when the property was placed in service and the type of property placed in service.
If you place property in service between January and September (the first nine months), you must use the half-year convention. This convention assumes you placed property in service in the middle of the year even if it was placed in service the beginning of the year. It also assumes that when you dispose of the property, you disposed of it in the middle of the year even if you dispose of it on January 1.
Consequently, in the year the property is placed in service you may only deduct one-half of the annual depreciation and in the year the property is disposed of you may only deduct one-half of the annual depreciation.
This convention considers the cost of business equipment (excluding realty) acquired in the last quarter of the year (October, November, and December). If the total cost of business equipment acquired in the last quarter of the year exceeds 40% of the total cost of equipment acquired for the entire year, the mid-quarter convention must be used for all property placed in service in that tax year.
For example, if total annual acquisitions equal $50,000, which includes last quarter acquisitions of $30,000, the mid-quarter convention must be used ($30,000/$60,000 = 60%).
The mid-month convention applies to realty. Only the straight-line method may be used for realty. For example, residential rental property.