Property and equipment is carried at cost less accumulated depreciation. When applicable, cost includes interest, real estate taxes and other costs incurred during construction. Also included in this category is internal-use software that is acquired, developed or modified solely to meet the Company's internal needs, with no plan to market externally. Costs directly related to acquiring, developing or modifying internal-use software are capitalized.
The Company calculates depreciation and amortization principally using the straight-line method generally based on the estimated useful life of each asset as follows: buildings and improvements, 10 to 40 years; purchased software, one to five years; internally developed software, three to seven years; and furniture and equipment (including computer equipment), three to 10 years. Improvements to leased facilities are depreciated over the remaining lease term or the estimated life of the improvement. The Company considers events and circumstances that would indicate the carrying value of property, equipment or capitalized software might not be recoverable. If the Company determines the carrying value of any of these assets is not recoverable, an impairment charge is recorded. See Note 8 for additional information.