A document published by the Internal Revenue Service (IRS) that outlines how to determine the cost basis for investments, real estate and business assets. The basis is used to determine what gain or loss is realized from a sale, and represents the cost of the investment or property. It is also used to determine depreciation and amortization for a piece of property.

The basis for a piece of property is typically the purchase cost, however the basis may increase over time if the owner makes improvements to the property. For investments, such as stocks and bonds, the cost basis also includes trading fees. More information on establishing the cost basis for investments can be found in IRS Publication 550.