Cost basis

Basis (or cost basis), as used in United States tax law, is the original cost of property, adjusted for factors such as depreciation. When property is sold, the taxpayer pays/(saves) taxes on a capital gain/(loss) that equals the amount realized on the sale minus the sold property's basis.

Cost basis is needed because tax is due based on the gain in value of an asset. For example, if a person buys a rock for $20, and sells the same rock for $20, there is no tax, since there is no profit. If, however, that person buys a rock for $20 and then sells the same rock for $25, then there is a capital gain on the rock of $5, which is thus taxable. The purchase price of $20 is analogous to cost of sales.

Typically, capital gains tax is due only when an asset is sold. However the rules for this are very complicated. If tax is paid because the value has increased, the new value will be the cost basis for any future tax.

Internal Revenue Service (IRS) Publication 551 contains the IRS's definition of basis: "Basis is the amount of your investment in property for tax purposes. Use the basis of property to figure depreciation, amortization, depletion, and casualty losses. Also use it to figure gain or loss on the sale or other disposition of property."

For federal income taxation purposes, determining basis depends on how the asset in question was acquired.

Assets acquired by purchase or contract: For assets purchased or acquired contractually, the basis equals the purchase price. See IRC (Internal Revenue Code) § 1012.

Assets acquired by gift or trust: The general rule is that assets acquired by gift or trust receive transferred basis (also called carryover basis). See IRC § 1015. Put simply, gifted assets retain the donor's basis. This means that the value of the asset at the time of transfer is irrelevant to computing the donee's new basis. The general rule does not apply, however, if at the time of transfer the donor's adjusted basis in the property exceeds its fair market value and the recipient disposes of the property at a loss. In this situation the asset's basis is its fair market value at the time of transfer. See Treas. Reg. § 1.1015-1(a)(1).

Assets acquired by inheritance: Assets acquired by inheritance are eligible to receive stepped-up basis, meaning the fair market value of the asset at the time of the decedent's death. See IRC § 1014. This provision shields the appreciation in value of the asset during the life of the decedent from any income taxation whatsoever.

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