General rule. (1) Interest at the annual rate referred to in the regulations under section 6621 shall be paid on any unpaid amount of tax from the last date prescribed for payment of the tax (determined without regard to any extension of time for payment) to the date on which payment is received.

For provisions requiring the payment of interest during the period occurring before July 1, 1975, see section 6601(a) prior to its amendment by section 7 of the Act of Jan. 3, 1975 (Pub. L. 93-625, 88 Stat. 2115).

Satisfaction by credits made after December 31, 1957—(1) In general. If any portion of a tax is satisfied by the credit of an overpayment after December 31, 1957, interest shall not be imposed under section 6601 on such portion of the tax for any period during which interest on the overpayment would have been allowable if the overpayment had been refunded.

Examples. The provisions of this paragraph may be illustrated by the following examples:

An examination of A's income tax returns for the calendar years 1955 and 1956 discloses an underpayment of $800 for 1955 and an overpayment of $500 for 1956. Interest under section 6601(a) ordinarily accrues on the underpayment of $800 from April 15, 1956, to the date of payment. However, the 1956 overpayment of $500 is credited after December 31, 1957, against the underpayment in accordance with the provisions of section 6402(a) and § 301.6402-1. Under such circumstances interest on the $800 underpayment runs from April 15, 1956, the last date prescribed for payment of the 1955 tax, to April 15, 1957, the date the overpayment of $500 was made. Since interest would have been allowed on the overpayment, if refunded, from April 15, 1957, to a date not more than 30 days prior to the date of the refund check, no interest is imposed after April 15, 1957, on $500, the portion of the underpayment satisfied by credit. Interest continues to run, however, on $300 (the $800 underpayment for 1955 less the $500 overpayment for 1956) to the date of payment.

An examination of A's income tax returns for the calendar years 1956 and 1957 discloses an overpayment, occurring on April 15, 1957, of $700 for 1956 and an underpayment of $400 for 1957. After April 15, 1958, the last date prescribed for payment of the 1957 tax, the district director credits $400 of the overpayment against the underpayment. In such a case, interest will accrue upon the overpayment of $700 from April 15, 1957, to April 15, 1958, the due date of the amount against which the credit is taken. Interest will also accrue under section 6611 upon $300 ($700 overpayment less $400 underpayment) from April 15, 1958, to a date not more than 30 days prior to the date of the refund check. Since a refund of the portion of the overpayment credited against the underpayment would have resulted in interest running upon such portion from April 15, 1958, to a date not more than 30 days prior to the date of the refund check, no interest is imposed upon the underpayment.

Last date prescribed for payment. (1) In determining the last date prescribed for payment, any extension of time granted for payment of tax (including any postponement elected under section 6163(a)) shall be disregarded. The granting of an extension of time for the payment of tax does not relieve the taxpayer from liability for the payment of interest thereon during the period of the extension. Thus, except as provided in paragraph (b) of this section, interest at the annual rate referred to in the regulations under section 6621 is payable on any unpaid portion of the tax for the period during which such portion remains unpaid by reason of an extension of time for the payment thereof.

If a tax or portion thereof is payable in installments in accordance with an election made under section 6152(a) or 6156(a), the last date prescribed for payment of any installment of such tax or portion thereof shall be determined under the provisions of section 6152(b) or 6156(b), as the case may be, and interest shall run on any unpaid installment from such last date to the date on which payment is received. However, in the event installment privileges are terminated for failure to pay an installment when due as provided by section 6152(d) and the time for the payment of any remaining installment is accelerated by the issuance of a notice and demand therefor, interest shall run on such unpaid installment from the date of the notice and demand to the date on which payment is received. But see section 6601(e)(4).

If the tax shown on a return is payable in installments, interest will run on any tax not shown on the return from the last date prescribed for payment of the first installment. If a deficiency is prorated to any unpaid installments, in accordance with section 6152(c), interest shall run on such prorated amounts from the date prescribed for the payment of the first installment to the date on which payment is received.

If, by reason of jeopardy, a notice and demand for payment of any tax is issued before the last date otherwise prescribed for payment, such last date shall nevertheless be used for the purpose of the interest computation, and no interest shall be imposed for the period commencing with the date of the issuance of the notice and demand and ending on such last date. If the tax is not paid on or before such last date, interest will automatically accrue from such last date to the date on which payment is received.

In the case of taxes payable by stamp and in all other cases where the last date for payment of the tax is not otherwise prescribed, such last date for the purpose of the interest computation shall be deemed to be the date on which the liability for the tax arose. However, such last date shall in no event be later than the date of issuance of a notice and demand for the tax.

Suspension of interest; waiver of restrictions on assessment. In the case of a deficiency determined by a district director (or an assistant regional commissioner, appellate) with respect to any income, estate, gift, or chapter 41, 42, 43, or 44 tax, if the taxpayer files with such internal revenue officer an agreement waiving the restrictions on assessment of such deficiency, and if notice and demand for payment of such deficiency is not made within 30 days after the filing of such waiver, no interest shall be imposed on the deficiency for the period beginning immediately after such 30th day and ending on the date notice and demand is made. In the case of an agreement with respect to a portion of the deficiency, the rules as set forth in this paragraph are applicable only to that portion of the deficiency to which the agreement relates.

Income tax reduced by carryback. (1) The carryback of a net operating loss, net capital loss, investment credit, or a work incentive program (WIN) credit shall not affect the computation of interest on any income tax for the period commencing with the last day prescribed for the payment of such tax and ending with the last day of the taxable year in which the loss or credit arises. For example, if the carryback of a net operating loss, a net capital loss, an investment credit, or a WIN credit to a prior taxable period eliminates or reduces a deficiency in income tax for that period, the full amount of the deficiency will nevertheless bear interest at the annual rate referred to in the regulations under section 6621 from the last date prescribed for payment of such tax until the last day of the taxable year in which the loss or credit arose. Interest will continue to run beyond such last day on any portion of the deficiency which is not eliminated by the carryback. With respect to any portion of an investment credit carryback or a WIN credit carryback from a taxable year attributable to a net operating loss carryback or a capital loss carryback from a subsequent taxable year, such investment credit carryback or WIN credit carryback shall not affect the computation of interest on any income tax for the period commencing with the last day prescribed for the payment of such tax and ending with the last day of such subsequent taxable year.

Where an extension of time for payment of income tax has been granted under section 6164 to a corporation expecting a net operating loss carryback or a net capital loss carryback, interest is payable at the annual rate established under section 6621 on the amount of such unpaid tax from the last date prescribed for payment thereof without regard to such extension.

Where there has been an allowance of an overpayment attributable to a net operating loss carryback, a capital loss carryback, an investment credit carryback, or a WIN credit carryback and all or part of such allowance is later determined to be excessive, interest shall be computed on the excessive amount from the last day of the year in which the net operating loss, net capital loss, investment credit, or WIN credit arose until the date on which the repayment of such excessive amount is received. Where there has been an allowance of an overpayment with respect to any portion of an investment credit carryback or a WIN credit carryback from a taxable year attributable to a net operating loss carryback or a capital loss carryback from a subsequent taxable year and all or part of such allowance is later determined to be excessive, interest shall be computed on the excessive amount from the last day of such subsequent taxable year until the date on which the repayment of such excessive amount is received.

Applicable rules. (1) Any interest prescribed by section 6601 shall be assessed and collected in the same manner as tax and shall be paid upon notice and demand by the district director or the director of the regional service center. Any reference in the Code (except in subchapter B, chapter 63, relating to deficiency procedures) to any tax imposed by the Code shall be deemed also to refer to the interest imposed by section 6601 on such tax. Interest on a tax may be assessed and collected at any time within the period of limitation on collection after assessment of the tax to which it relates. For rules relating to the period of limitation on collection after assessment, see section 6502.

No interest under section 6601 shall be payable on any interest provided by such section. This paragraph (f)(2) shall not apply after December 31, 1982, with respect to interest accruing after such date, or accrued but unpaid on such date. See § 301.6622-1.

Interest will not be imposed on any assessable penalty, addition to the tax (other than an addition to tax described in section 6601(e)(2)(B)), or additional amount if the amount is paid within 21 calendar days (10 business days if the amount assessed and shown on the notice and demand equals or exceeds $100,000) from the date of the notice and demand. If interest is imposed, it will be imposed only for the period from the date of the notice and demand to the date on which payment is received. This paragraph (f)(3) is applicable with respect to any notice and demand made after December 31, 1996.

If notice and demand is made after December 31, 1996, for any amount and the amount is paid within 21 calendar days (10 business days if the amount assessed and shown on the notice and demand equals or exceeds $100,000) from the date of the notice and demand, interest will not be imposed for the period after the date of the notice and demand.

For purposes of paragraphs (f)(3) and (4) of this section—

The term business day means any day other than a Saturday, Sunday, legal holiday in the District of Columbia, or a statewide legal holiday in the state where the taxpayer resides or where the taxpayer's principal place of business is located. With respect to the tenth business day (after taking into account the first sentence of this paragraph (f)(5)(i)), see section 7503 relating to time for performance of acts where the last day falls on a statewide legal holiday in the state where the act is required to be performed.

The term calendar day means any day. With respect to the twenty-first calendar day, see section 7503 relating to time for performance of acts where the last day falls on a Saturday, Sunday, or legal holiday.

No interest shall be imposed for failure to pay estimated tax as required by section 59 of the Internal Revenue Code of 1939 or section 6153 or 6154 of the Internal Revenue Code of 1954.