26 CFR § 1.167(a)-1 - Depreciation in general.
(a) Reasonable allowance. Section 167(a) provides that a reasonable allowance for the exhaustion, wear and tear, and obsolescence of property used in the trade or business or of property held by the taxpayer for the production of income shall be allowed as a depreciation deduction. The allowance is that amount which should be set aside for the taxable year in accordance with a reasonably consistent plan (not necessarily at a uniform rate), so that the aggregate of the amounts set aside, plus the salvage value, will, at the end of the estimated useful life of the depreciable property, equal the cost or other basis of the property as provided in section 167(g) and § 1.167(g)–1. An asset shall not be depreciated below a reasonable salvage value under any method of computing depreciation. However, see section 167(f) and § 1.167(f)–1 for rules which permit a reduction in the amount of salvage value to be taken into account for certain personal property acquired after October 16, 1962. See also paragraph (c) of this section for definition of salvage. The allowance shall not reflect amounts representing a mere reduction in market value. See section 179 and § 1.179–1 for a further description of the term “reasonable allowance.”
(b) Useful life. For the purpose of section 167 the estimated useful life of an asset is not necessarily the useful life inherent in the asset but is the period over which the asset may reasonably be expected to be useful to the taxpayer in his trade or business or in the production of his income. This period shall be determined by reference to his experience with similar property taking into account present conditions and probable future developments. Some of the factors to be considered in determining this period are (1) wear and tear and decay or decline from natural causes, (2) the normal progress of the art, economic changes, inventions, and current developments within the industry and the taxpayer's trade or business, (3) the climatic and other local conditions peculiar to the taxpayer's trade or business, and (4) the taxpayer's policy as to repairs, renewals, and replacements. Salvage value is not a factor for the purpose of determining useful life. If the taxpayer's experience is inadequate, the general experience in the industry may be used until such time as the taxpayer's own experience forms an adequate basis for making the determination. The estimated remaining useful life may be subject to modification by reason of conditions known to exist at the end of the taxable year and shall be redetermined when necessary regardless of the method of computing depreciation. However, estimated remaining useful life shall be redetermined only when the change in the useful life is significant and there is a clear and convincing basis for the redetermination. For rules covering agreements with respect to useful life, see section 167(d) and § 1.167(d)–1. If a taxpayer claims an investment credit with respect to an asset for a taxable year preceding the taxable year in which the asset is considered as placed in service under § 1.167(a)–10(b) or § 1.167(a)–11(e), the useful life of the asset under this paragraph shall be the same useful life assigned to the asset under § 1.46–3(e).
(1) Salvage value is the amount (determined at the time of acquisition) which is estimated will be realizable upon sale or other disposition of an asset when it is no longer useful in the taxpayer's trade or business or in the production of his income and is to be retired from service by the taxpayer. Salvage value shall not be changed at any time after the determination made at the time of acquisition merely because of changes in price levels. However, if there is a redetermination of useful life under the rules of paragraph (b) of this section, salvage value may be redetermined based upon facts known at the time of such redetermination of useful life. Salvage, when reduced by the cost of removal, is referred to as net salvage. The time at which an asset is retired from service may vary according to the policy of the taxpayer. If the taxpayer's policy is to dispose of assets which are still in good operating condition, the salvage value may represent a relatively large proportion of the original basis of the asset. However, if the taxpayer customarily uses an asset until its inherent useful life has been substantially exhausted, salvage value may represent no more than junk value. Salvage value must be taken into account in determining the depreciation deduction either by a reduction of the amount subject to depreciation or by a reduction in the rate of depreciation, but in no event shall an asset (or an account) be depreciated below a reasonable salvage value. See, however, paragraph (a) of § 1.167(b)–2 for the treatment of salvage under the declining balance method, and § 1.179–1 for the treatment of salvage in computing the additional first-year depreciation allowance. The taxpayer may use either salvage or net salvage in determining depreciation allowances but such practice must be consistently followed and the treatment of the costs of removal must be consistent with the practice adopted. For specific treatment of salvage value, see §§ 1.167(b)–1, 1.167(b)–2, and 1.167(b)–3. When an asset is retired or disposed of, appropriate adjustments shall be made in the asset and depreciation reserve accounts. For example, the amount of the salvage adjusted for the costs of removal may be credited to the depreciation reserve.
(2) For taxable years beginning after December 31, 1961, and ending after October 16, 1962, see section 167(f) and § 1.167(f)–1 for rules applicable to the reduction of salvage value taken into account for certain personal property acquired after October 16, 1962.