The Doctrine of Constructive Receipt is a taxation principle that taxes income before that income is actually received. It says that that gross income under a taxpayer's control before it is actually received must be included by the taxpayer in gross income, unless the actual receipt is subject to significant constraints. Therefore according to this doctrine, even if the income is not actually received, the fact that the person could have had it if s/he had simply requested it, means that for all intents and tax purposes, that the person did have it.
Internal Revenue Code Section 1.451-2(a) outlines the constructive receipt doctrine. It states that income although not actually in a taxpayer’s possession, is constructively received in the taxable year during which it is credited to the taxpayer’s account, set apart for the taxpayer, or otherwise made available so that the taxpayer may draw upon it during the taxable year if notice of intention to withdraw had been given. Income is not constructively received if the taxpayer’s control of its receipt is subject to substantial limitations or restrictions.