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Fair market value (FMV) is an estimate of the market value of a property, based on what a knowledgeable, willing, and unpressured buyer would probably pay to a knowledgeable, willing, and unpressured seller in the market. An estimate of fair market value may be founded either on precedent or extrapolation. Fair market value differs from the intrinsic value that an individual may place on the same asset based on their own preferences and circumstances.
Since market transactions are often not observable for assets such as privately held businesses and most personal and real property, FMV must be estimated. An estimate of fair market value is usually subjective due to the circumstances of place, time, the existence of comparable precedents, and the evaluation principles of each involved person. Opinions on value are always based upon subjective interpretation of available information at the time of assessment. This is in contrast to an imposed value, in which a legal authority (law, tax regulation, court, etc.) sets an absolute value upon a product or a service.
An eminent domain taking, in lieu of a property sale, would not be considered a fair market transaction since one of the parties (in this case, the seller) was under undue pressure to enter into the transaction. Other examples of sales that would not meet the test of fair market value include a liquidation sale, deed in lieu of foreclosure, distressed sale, and similar types of transactions.
- The fair market value is the price at which the property would change hands between a willing buyer and a willing seller, neither being under any compulsion to buy or to sell and both having reasonable knowledge of relevant facts. United States v. Cartwright, 411 U. S. 546, 93 S. Ct. 1713, 1716-17, 36 L. Ed. 2d 528, 73-1 U.S. Tax Cas. ( CCH) ¶ 12,926 (1973) (quoting from U.S. Treasury regulations relating to Federal estate taxes, at 26 C.F.R. sec. 20.2031-1(b)). 
The term fair market value is used throughout the Internal Revenue Code among other federal statutory laws in the USA including Bankruptcy, many state laws, and several regulatory bodies.  In litigation in many jurisdictions in the United States, the fair market value is determined at a hearing. In certain jurisdictions, the courts are required to hold fair market hearings, even if the borrowers or the loans guarantors waived their rights to such a hearing in the loan documents. 
Fair market value is not explicitly defined in the Income Tax Act. That said, Mr. Justice Cattanach in Henderson Estate, Bank of New York v. M.N.R., (1973) C.T.C. 636 at p. 644 articulates the concept as follows:
The statute does not define the expression "fair market value", but the expression has been defined in many different ways depending generally on the subject matter which the person seeking to define it had in mind. I do not think it necessary to attempt an exact definition of the expression as used in the statute other than to say that the words must be construed in accordance with the common understanding of them. That common understanding I take to mean the highest price an asset might reasonably be expected to bring if sold by the owner in the normal method applicable to the asset in question in the ordinary course of business in a market not exposed to any undue stresses and composed of willing buyers and sellers dealing at arm's length and under no compulsion to buy or sell. I would add that the foregoing understanding as I have expressed it in a general way includes what I conceive to be the essential element which is an open and unrestricted market in which the price is hammered out between willing and informed buyers and sellers on the anvil of supply and demand. These definitions are equally applicable to "fair market value" and "market value" and it is doubtful if the word "fair" adds anything to the words "market value."
In concert with this decision, the Canada Revenue Agency (CRA) lists the following working definition in its on-line dictionary:
Fair market value generally means the highest price, expressed in dollars, that a property would bring in an open and unrestricted market between a willing buyer and a willing seller who are both knowledgeable, informed, and prudent, and who are acting independently of each other. 
As the definition indicates, the Canadian and American concepts of fair market value are very similar. One obvious difference is that the Canadian working definition refers to "the highest price" whereas the American definition merely mentions "the price." It is debatable whether or not the presence of the word "highest" distinguishes the Canadian from the American definition.
- United States v. Cartwright, 411 U.S. 546, 551 (1973) ("The fair market value is the price at which the property would change hands between a willing buyer and a willing seller, neither being under any compulsion to buy or to sell and both having reasonable knowledge of relevant facts.").
- to wit, Internal Revenue Service Notice 2005-43
- Jenkins Jr., W. Scott; Alissa A. Brice; Ryley Carlock & Applewhite, PC (20 April 2014). "The Arizona Court of Appeals Holds the Right to a Fair Market Value Hearing Cannot be Waived in a Deficiency Action". The National Law Review. Retrieved 5 May 2014.
- "Fair Market Value" Archived 2014-08-06 at the Wayback Machine. Canada Revenue Agency Dictionary. Retrieved 20 May 2014.