The cost recovery periods for most real property are 39 years for nonresidential real property and 27.5 years for residential rental property. The straight line depreciation method and mid-month convention are required for such real property.

Under pre-Act law, qualified leasehold improvement property was an interior building improvement to nonresidential real property, by a landlord, tenant or subtenant, that was placed in service more than three years after the building is and that meets other requirements. Qualified restaurant property was either (a) a building improvement in a building in which more than 50% of the building's square footage was devoted to the preparation of, and seating for, on-premises consumption of prepared meals (the more-than-50% test), or (b) a building that passed the more-than-50% test. Qualified retail improvement property was an interior improvement to retail space that was placed in service more than three years after the date the building was first placed in service and that meets other requirements.

Qualified improvement property is any improvement to an interior portion of a building that is nonresidential real property if such improvement is placed in service after the date such building was first placed in service. Qualified improvement property does not include any improvement for which the expenditure is attributable to the enlargement of the building, any elevator or escalator, or the internal structural framework of the building.

If a taxpayer elected the ADS, residential rental property had a recovery period of 40 years. ADS is principally a straight-line depreciation system under which one depreciation period (generally longer than any other) is prescribed for each class of recovery property.

New law. For property placed in service after Dec. 31, 2017, the separate definitions of qualified leasehold improvement, qualified restaurant, and qualified retail improvement property are eliminated, a general 15-year recovery period and straight-line depreciation are provided for qualified improvement property, and a 20-year ADS recovery period is provided for such property.

Thus, qualified improvement property placed in service after Dec. 31, 2017, is generally depreciable over 15 years using the straight-line method and half-year convention, without regard to whether the improvements are property subject to a lease, placed in service more than three years after the date the building was first placed in service, or made to a restaurant building. Restaurant building property placed in service after Dec. 31, 2017, that does not meet the definition of qualified improvement property, is depreciable as nonresidential real property, using the straight-line method and the mid-month convention.

For property placed in service after Dec. 31, 2017, the ADS recovery period for residential rental property is shortened from 40 years to 30 years.

For tax years beginning after Dec. 31, 2017, an electing farming business—i.e., a farming business electing out of the limitation on the deduction for interest—must use ADS to depreciate any property with a recovery period of 10 years or more (e.g., a single purpose agricultural or horticultural structures, trees or vines bearing fruit or nuts, farm buildings, and certain land improvements).