IRS Publication 946 at https://www.irs.gov/pub/irs-prior/p946--2019.pdf covers all the methods and conventions used to depreciate property. Typically, residential rental real estate that is located in the United States is depreciated over 27.5 years, using the mid-month convention, straight line depreciation method as shown in table A-6 on page 72 of that publication. The TurboTax program uses this automatically, by default for residential rental property located in the United States.