26 C.F.R. § 301.6651-1 : Internal Revenue — INTERNAL REVENUE SERVICE, DEPARTMENT OF THE TREASURY — PROCEDURE AND ADMINISTRATION — PROCEDURE AND ADMINISTRATION —ADDITIONS TO THE TAX, ADDITIONAL AMOUNTS, AND ASSESSABLE PENALTIES —ADDITIONS TO THE TAX AND ADDITIONAL AMOUNTS —1 - Failure to file tax return or to pay tax

(a) Addition to the tax -
(1) Failure to file tax return. In case of failure to file a return required under authority of-
(i) Subchapter A, chapter 61 of the Code, relating to returns and records (other than sections 6015 and 6016, relating to declarations of estimated tax, and part III thereof, relating to information returns);
(ii) Subchapter A, chapter 51 of the Code, relating to distilled spirits, wines, and beer;
(iii) Subchapter A, chapter 52 of the Code, relating to cigars, cigarettes, and cigarette papers and tubes; or
(iv) Subchapter A, chapter 53 of the Code, relating to machine guns, destructive devices, and certain other firearms; and

The regulations thereunder, on or before the date prescribed for filing (determined with regard to any extension of time for such filing), there shall be added to the tax required to be shown on the return the amount specified below unless the failure to file the return within the prescribed time is shown to the satisfaction of the district director or the director of the service center to be due to reasonable cause and not to willful neglect. The amount to be added to the tax is 5 percent thereof if the failure is for not more than 1 month, with an additional 5 percent for each additional month or fraction thereof during which the failure continues, but not to exceed 25 percent in the aggregate. The amount of any addition under this subparagraph shall be reduced by the amount of the addition under subparagraph (2) of this paragraph for any month to which an addition to tax applies under both subparagraphs (1) and (2) of this paragraph (a).

(2) Failure to pay tax shown on return. In case of failure to pay the amount shown as tax on any return (required to be filed after December 31, 1969, without regard to any extension of time for filing thereof) specified in subparagraph (1) of this paragraph (a), on or before the date prescribed for payment of such tax (determined with regard to any extension of time for payment), there shall be added to the tax shown on the return the amount specified below unless the failure to pay the tax within the prescribed time is shown to the satisfaction of the district director, or, as provided in paragraph (a) of this section, the Assistant Regional Commissioner (Alcohol, Tobacco and Firearms), the director of the service center, to be due to reasonable cause and not to willful neglect. Except as provided in paragraph (a)(4) of this section, the amount to be added to the tax is 0.5 percent of the amount of tax shown on the return if the failure is for not more than 1 month, with an additional 0.5 percent for each additional month or fraction thereof during which the failure continues, but not to exceed 25 percent in the aggregate.
(3) Failure to pay tax not shown on return. In the case of failure to pay any amount of any tax required to be shown on a return specified in paragraph (a)(1) of this section that is not so shown (including an assessment made pursuant to section 6213(b)) within 21 calendar days from the date of the notice and demand (10 business days if the amount assessed and shown on the notice and demand equals or exceeds $100,000) with respect to any notice and demand made after December 31, 1996, there will be added to the amount stated in the notice and demand the amount specified below unless the failure to pay the tax within the prescribed time is shown to the satisfaction of the district director or the director of the service center to be due to reasonable cause and not to willful neglect. Except as provided in paragraph (a)(4) of this section, the amount to be added to the tax is 0.5 percent of the amount stated in the notice and demand if the failure is for not more than 1 month, with an additional 0.5 percent for each additional month or fraction thereof during which the failure continues, but not to exceed 25 percent in the aggregate. For purposes of this paragraph (a)(3), see §301.6601-1(f)(5) for the definition of calendar day and business day.
(4) Reduction of failure to pay penalty during the period an installment agreement is in effect -
(i) In general. In the case of a return filed by an individual on or before the due date for the return (including extensions)-
(A) The amount added to tax for a month or fraction thereof is determined by using 0.25 percent instead of 0.5 percent under paragraph (a)(2) of this section if at any time during the month an installment agreement under section 6159 is in effect for the payment of such tax; and
(B) The amount added to tax for a month or fraction thereof is determined by using 0.25 percent instead of 0.5 percent under paragraph (a)(3) of this section if at any time during the month an installment agreement under section 6159 is in effect for the payment of such tax.
(ii) Effective date. This paragraph (a)(4) applies for purposes of determining additions to tax for months beginning after December 31, 1999.
(b) Month defined.
(1) If the date prescribed for filing the return or paying tax is the last day of a calendar month, each succeeding calendar month or fraction thereof during which the failure to file or pay tax continues shall constitute a month for purposes of section 6651.
(2) If the date prescribed for filing the return or paying tax is a date other than the last day of a calendar month, the period which terminates with the date numerically corresponding thereto in the succeeding calendar month and each such successive period shall constitute a month for purposes of section 6651. If, in the month of February, there is no date corresponding to the date prescribed for filing the return or paying tax, the period from such date in January through the last day of February shall constitute a month for purposes of section 6651. Thus, if a return is due on January 30, the first month shall end on February 28 (or 29 if a leap year), and the succeeding months shall end on March 30, April 30, etc.
(3) If a return is not timely filed or tax is not timely paid, the fact that the date prescribed for filing the return or paying tax, or the corresponding date in any succeeding calendar month, falls on a Saturday, Sunday, or a legal holiday is immaterial in determining the number of months for which the addition to the tax under section 6651 applies.
(c) Showing of reasonable cause.
(1) Except as provided in subparagraphs (3) and (4) of this paragraph (b), a taxpayer who wishes to avoid the addition to the tax for failure to file a tax return or pay tax must make an affirmative showing of all facts alleged as a reasonable cause for his failure to file such return or pay such tax on time in the form of a written statement containing a declaration that it is made under penalties of perjury. Such statement should be filed with the district director or the director of the service center with whom the return is required to be filed; Provided, That where special tax returns of liquor dealers are delivered to an alcohol, tobacco and firearms officer working under the supervision of the Regional Director, Bureau of Alcohol, Tobacco and Firearms, such statement may be delivered with the return. If the district director, the director of the service center, or, where applicable, the Regional Director, Bureau of Alcohol, Tobacco and Firearms, determines that the delinquency was due to a reasonable cause and not to willful neglect, the addition to the tax will not be assessed. If the taxpayer exercised ordinary business care and prudence and was nevertheless unable to file the return within the prescribed time, then the delay is due to a reasonable cause. A failure to pay will be considered to be due to reasonable cause to the extent that the taxpayer has made a satisfactory showing that he exercised ordinary business care and prudence in providing for payment of his tax liability and was nevertheless either unable to pay the tax or would suffer an undue hardship (as described in §1.6161-1(b) of this chapter) if he paid on the due date. In determining whether the taxpayer was unable to pay the tax in spite of the exercise of ordinary business care and prudence in providing for payment of his tax liability, consideration will be given to all the facts and circumstances of the taxpayer's financial situation, including the amount and nature of the taxpayer's expenditures in light of the income (or other amounts) he could, at the time of such expenditures, reasonably expect to receive prior to the date prescribed for the payment of the tax. Thus, for example, a taxpayer who incurs lavish or extravagant living expenses in an amount such that the remainder of his assets and anticipated income will be insufficient to pay his tax, has not exercised ordinary business care and prudence in providing for the payment of his tax liability. Further, a taxpayer who invests funds in speculative or illiquid assets has not exercised ordinary business care and prudence in providing for the payment of his tax liability unless, at the time of the investment, the remainder of the taxpayer's assets and estimated income will be sufficient to pay his tax or it can be reasonably foreseen that the speculative or illiquid investment made by the taxpayer can be utilized (by sale or as security for a loan) to realize sufficient funds to satisfy the tax liability. A taxpayer will be considered to have exercised ordinary business care and prudence if he made reasonable efforts to conserve sufficient assets in marketable form to satisfy his tax liability and nevertheless was unable to pay all or a portion of the tax when it became due.
(2) In determining if the taxpayer exercised ordinary business care and prudence in providing for the payment of his tax liability, consideration will be given to the nature of the tax which the taxpayer has failed to pay. Thus, for example, facts and circumstances which, because of the taxpayer's efforts to conserve assets in marketable form, may constitute reasonable cause for nonpayment of income taxes may not constitute reasonable cause for failure to pay over taxes described in section 7501 that are collected or withheld from any other person.
(3) If, for a taxable year ending on or after December 31, 1995, an individual taxpayer satisfies the requirement of § 1.6081-4(a) of this chapter (relating to automatic extension of time for filing an individual income tax return), reasonable cause will be presumed, for the period of the extension of time to file, with respect to any underpayment of tax if-
(i) The excess of the amount of tax shown on the individual income tax return over the amount of tax paid on or before the regular due date of the return (by virtue of tax withheld by the employer, estimated tax payments, and any payment with an application for extension of time to file pursuant to §1.6081-4 of this chapter) is no greater than 10 percent of the amount of tax shown on the individual income tax return; and
(ii) Any balance due shown on the individual income tax return is remitted with the return.
(4) If, for a taxable year ending on or after December 31, 1972, a corporate taxpayer satisfies the requirements of §1.6081-3 (a) (relating to an automatic extension of time for filing a corporation income tax return), reasonable cause shall be presumed, for the period of the extension of time to file, with respect to any underpayment of tax if-
(i) The amount of tax (determined without regard to any prepayment thereof) shown on Form 7004, or the amount of tax paid on or before the regular due date of the return, is at least 90 percent of the amount of tax shown on the taxpayer's Form 1120, and
(ii) Any balance due shown on the Form 1120 is paid on, or before the due date of the return, including any extensions of time for filing.
(d) Penalty imposed on net amount due -
(1) Credits against the tax. The amount of tax required to be shown on the return for purposes of section 6651(a)(1) and the amount shown as tax on the return for purposes of section 6651(a)(2) shall be reduced by the amount of any part of the tax which is paid on or before the date prescribed for payment of the tax and by the amount of any credit against the tax which may be claimed on the return.
(2) Partial payments.
(i) The amount of tax required to be shown on the return for purposes of section 6651(a)(2) shall, for the purpose of computing the addition for any month, be reduced by the amount of any part of the tax which is paid after the date prescribed for payment and on or before the first day of such month.
(ii) The amount of tax stated in the notice and demand for purposes of section 6651(a)(3) shall, for the purpose of computing the addition for any month, be reduced by the amount of any part of the tax which is paid before the first day of such month.
(e) No addition to tax if fraud penalty assessed. No addition to the tax under section 6651 shall be assessed with respect to an underpayment of tax if a 50-percent addition to the tax for fraud is assessed with respect to the same underpayment under section 6653(b). See section 6653(d).
(f) Examples. The provisions of this section may be illustrated by the following examples:
Example 1.
(a) Under section 6072(a), income tax returns of individuals on a calendar year basis must be filed on or before the 15th day of April following the close of the calendar year. Assume an individual filed his income tax return for the calendar year 1969 on July 20, 1970, and the failure to file on or before the prescribed date is not due to reasonable cause. The tax shown on the return is $800 and a deficiency of $200 is subsequently assessed, making the tax required to be shown on the return, $1,000. Of this amount, $300 has been paid by withholding from wages and $400 has been paid as estimated tax. The balance due as shown on the return of $100 ($800 shown as tax on the return less $700 previously paid) is paid on August 21, 1970. The failure to pay on or before the prescribed date is not due to reasonable cause. There will be imposed, in addition to interest, an additional amount under section 6651(a)(2) of $2.50, which is 2.5 percent (2% for the 4 months from April 16 through August 15, and 0.5% for the fractional part of the month from August 16 through August 21) of the net amount due as shown on the return of $100 ($800 shown on the return less $700 paid on or before April 15). There will also be imposed an additional amount under section 6651(a)(1) of $58, determined as follows:

20 percent (5% per month for the 3 months from April 16 through July 15 and 5% for the fractional part of the month from July 16 through July 20) of the net amount due of $300 ($1,000 required to be shown on the return less $700 paid on or before April 15) $60
Reduced by the amount of the addition imposed under section 6651(a)(2) for those months 2
Addition to tax under section 6651(a)(1) $50

(b) A notice and demand for the $200 deficiency is issued on January 8, 1971, but the taxpayer does not pay the deficiency until December 23, 1971. In addition to interest there will be imposed an additional amount under section 6651(a)(3) of $10, determined as follows:

Addition computed without regard to limitation:
6 percent (5 1/2% for the 11 months from January 19, 1971, through December 18, 1971, and 0.5% for the fractional part of the month from December 19 through December 23) of the amount stated in the notice and demand ($200) $12
Limitation on addition:
25 percent of the amount stated in the notice and demand ($200) $50
Reduced by the part of the addition under section 6651(a)(1) for failure to file attributable to the $200 deficiency (20% of $200) $40
Maximum amount of the addition under section 6651(a)(3) $10

Example 2. An individual files his income tax return for the calendar year 1969 on December 2, 1970, and such delinquency is not due to reasonable cause. The balance due, as shown on the return, of $500 is paid when the return is filed on December 2, 1970. In addition to interest and the addition for failure to pay under section 6651(a)(2) of $20 (8 months at 0.5% per month, 4%), there will also be imposed an additional amount under section 6651(a)(1) of $112.50, determined as follows:

Penalty at 5 percent for maximum of 5 months, 25 percent of $500 $125.00
Less reduction for the amount of the addition under section 6651(a)(2):
Amount imposed under section 6651(a)(2) for the months in which there is also an addition for failure to file-2 1/2 percent for the 5 months April 16 through September 15 of the net amount due ($500) 12.50
Addition to tax under section 6651(a)(1) $112.50

(g) Treatment of returns prepared by the Secretary -
(1) In general. A return prepared by the Secretary under section 6020(b) will be disregarded for purposes of determining the amount of the addition to tax for failure to file any return pursuant to paragraph (a)(1) of this section. However, the return prepared by the Secretary will be treated as a return filed by the taxpayer for purposes of determining the amount of the addition to tax for failure to pay the tax shown on any return and for failure to pay the tax required to be shown on a return that is not so shown pursuant to paragraphs (a)(2) and (3) of this section, respectively.
(2) Effective date. This paragraph (g) applies to returns the due date for which (determined without regard to extensions) is after July 30, 1996.

26 C.F.R. §301.6651-1

T.D. 7133, 36 FR 13594, 7/22/1971, as amended by T.D. 7160, 37 FR 2507, 2/2/1972; T.D. 7260, 38 FR 4259, 2/12/1973; T.D. 8651, 61 FR 262, 1/4/1996; T.D. 8703, 61 FR 69031, 12/31/1996; T.D. 8725, 62 FR 39117, 7/22/1997; T.D. 8895, 65 FR 50408, 8/18/2000; T.D. 9163, 69 FR 70550, 12/7/2004