The alternate depreciation system (ADS) is used to calculate the allowable depreciation for alternative minimum tax purposes.  The ADS generally uses straight-line depreciation over longer tax lives than that for MACRS.  However, tangible personal property with a class life of 3, 5, 7, or 10 years that uses regular MACRS depreciation must use 150% declining balance depreciation with optimal switch to straight-line over the MACRS class life for alternative minimum tax purposes.  A straight-line election can be made under MACRS to depreciate property over either the class life of the property or the ADS life.  Thus, taxpayers can elect to use ADS to calculate depreciation for regular tax purposes