26 CFR § 1.31-1 - Credit for tax withheld on wages.
(a) The tax deducted and withheld at the source upon wages under chapter 24 of the Internal Revenue Code of 1954 (or in the case of amounts withheld in 1954, under subchapter D, chapter 9 of the Internal Revenue Code of 1939) is allowable as a credit against the tax imposed by Subtitle A of the Internal Revenue Code of 1954, upon the recipient of the income. If the tax has actually been withheld at the source, credit or refund shall be made to the recipient of the income even though such tax has not been paid over to the Government by the employer. For the purpose of the credit, the recipient of the income is the person subject to tax imposed under Subtitle A upon the wages from which the tax was withheld. For instance, if a husband and wife domiciled in a State recognized as a community property State for Federal tax purposes make separate returns, each reporting for income tax purposes one- half of the wages received by the husband, each spouse is entitled to one-half of the credit allowable for the tax withheld at source with respect to such wages.
(b) The tax withheld during any calendar year shall be allowed as a credit against the tax imposed by Subtitle A for the taxable year of the recipient of the income which begins in that calendar year. If such recipient has more than one taxable year beginning in that calendar year, the credit shall be allowed against the tax for the last taxable year so beginning.