(a) Early return or advance payment of tax. For purposes of section 6511, a return filed before the last day prescribed by law or regulations for the filing thereof shall be considered as filed on such last day. For purposes of section 6511 (b)(2) and (c) and section 6512, payment of any portion of the tax made before the last day prescribed for payment shall be considered made on such last day. An extension of time for filing a return or for paying any tax, or an election to pay any tax in installments, shall not be given any effect in determining under this section the last day prescribed for filing a return or paying any tax.

(b) Prepaid income tax. For purposes of section 6511 (relating to limitations on credit or refund) or section 6512 (relating to limitations in case of petition to Tax Court)—

(1) Any tax actually deducted and withheld at the source during any calendar year under chapter 24 of the Code (relating to collection of income tax at source on wages) shall, in respect of the recipient of the income, be deemed to have been paid by him on the 15th day of the fourth month following the close of his taxable year with respect to which such tax is allowable as a credit under section 31 (relating to tax withheld on wages),

(2) Any amount paid as estimated income tax for any taxable year shall be deemed to have been paid on the last day prescribed for filing the income tax return under section 6012 for such taxable year (determined without regard to any extension of time for filing such return), and

(3) Any tax withheld at the source on or after November 13, 1966, under chapter 3 of the Code (relating to tax withheld on nonresident aliens and foreign corporations and tax-free covenant bonds) shall, in respect of the recipient of the income, be deemed to have been paid by such recipient on the last day prescribed for filing his income tax return under section 6012 for the taxable year (determined without regard to any extension of time for filing such return) with respect to which such tax is allowable as a credit under section 1462 (relating to withheld tax as credit to recipient of income).

(c) Return and payment of social security taxes and income tax withholding. Notwithstanding paragraph (a) of this section, if a return (or payment) on or after November 13, 1966, of tax imposed by chapter 3 of the Code (relating to withholding of tax on nonresident aliens and foreign corporations and tax-free covenant bonds), or if a return (or payment) of tax imposed by chapter 21 of the Code (relating to the Federal Insurance Contributions Act) or by chapter 24 of the Code (relating to the collection of income tax at source on wages), for any period ending with or within a calendar year is filed or paid before April 15 of the succeeding calendar year, for purposes of section 6511 (relating to limitations on credit or refund) the return shall be considered filed, or the tax considered paid, on April 15 of such succeeding calendar year.

(d) Overpayment of income tax credited to estimated tax. If a taxpayer elects under the provisions of section 6402(b) to credit an overpayment of income tax for a taxable year against estimated tax for the succeeding taxable year, the amount so credited shall be considered a payment of income tax for such succeeding taxable year (whether or not claimed as a credit on the estimated tax return for such succeeding taxable year). If the treatment of such amount as a payment of income tax for the succeeding taxable year results in an overpayment for such succeeding taxable year, the period of limitations applicable to such overpayment is determined by reference to that taxable year. An election so to credit an overpayment of income tax precludes the allowance of a claim for credit or refund of such overpayment for the taxable year in which the overpayment arises.