Net property includes land, buildings and land improvements, machinery and equipment, tooling, and other assets that we use in our normal operations. These assets are recorded at cost, net of accumulated depreciation and impairments. We capitalize new assets when we expect to use the asset for more than one year. Routine maintenance and repair costs are expensed when incurred.
Property and equipment are depreciated primarily using the straight-line method over the estimated useful life of the asset. Useful lives range from 3 years to 36 years. The estimated useful lives generally are 14.5 years for machinery and equipment, 3 years for software (8 years for mainframe and client based software), 30 years for land improvements, and 36 years for buildings. Tooling generally is amortized over the expected life of a product program using a straight-line method. If the expected production volumes for major product programs associated with tooling decline significantly, we accelerate the amortization reflecting the rate of decline.
