Treasury Regulations · 26 CFR
§ 1.6664-2. Underpayment.
Regulation text, no changes From the eCFR, current as of October 15, 2026. The eCFR is an authoritative but unofficial editorial compilation of the Code of Federal Regulations; the official text is the annual CFR on govinfo. Compare it with this section on ecfr.gov (external site) or the official annual CFR on govinfo (external site).
Regulation under 26 U.S.C. § 6664
Cite as 26 CFR § 1.6664-2
At a glance
Read from the text and its source citation. Not part of the regulation.
- Status
- In the current eCFR
- Issued
- December 31, 1991 by T.D. 8381
- Last amended
- January 9, 2007 by T.D. 9309
- Issued under
- 26 U.S.C. § 6664
- Length
- 2,965 words · about 13 min to read
- Defines
- 1 term
- Cross-references
- cites 14 Code sections and 4 regulations; cited by 13
The definition of underpayment also may be expressed as—
Underpayment = W − (X + Y − Z),
where W = the amount of income tax imposed; X = the amount shown as the tax by the taxpayer on his return; Y = amounts not so shown previously assessed (or collected without assessment); and Z = the amount of rebates made.
T, an individual taxpayer, claimed tax benefits on its 2002 Federal income tax return from a transaction that is substantially similar to the transaction identified as a listed transaction in Notice 2002-65, 2002-2 C.B. 690 (Partnership Entity Straddle Tax Shelter). T did not disclose his participation in this transaction on a Form 8886, “Reportable Transaction Disclosure Statement,” as required by § 1.6011-4. On June 30, 2004, the IRS requested from P, T's material advisor, an investor list required to be maintained under section 6112. The section 6112 request, however, related to the type of transaction described in Notice 2003-81, 2003-2 C.B. 1223 (Tax Avoidance Using Offsetting Foreign Currency Option Contracts). T did not participate in (within the meaning of § 1.6011-4(c)) a transaction described in Notice 2003-81. T may file a qualified amended return relating to the transaction described in Notice 2002-65 because T did not claim a tax benefit with respect to the listed transaction described in Notice 2003-81, which is the subject of the section 6112 request.
The facts are the same as in Example 1, except that T's 2002 Federal income tax return reflected T's participation in the transaction described in Notice 2003-81. As of June 30, 2004, T may not file a qualified amended return for the 2002 tax year.
(i) Corporation X claimed tax benefits from a transaction on its 2002 Federal income tax return. In October 2004, the IRS and Treasury Department identified the transaction as a listed transaction. In December 2004, the IRS contacted P concerning an examination of P's liability under section 6707(a) (as in effect prior to the amendment to section 6707 by section 816 of the American Jobs Creation Act of 2004 (the Jobs Act), Public Law 108-357 (118 Stat. 1418)). P is the organizer of a section 6111 tax shelter (as in effect prior to the amendment to section 6111 by section 815 of the Jobs Act) who provided representations to X regarding tax benefits from the transaction, and the IRS has contacted P about the failure to register that transaction. Three days later, X filed an amended return.
(ii) X's amended return is not a qualified amended return, because X did not disclose the transaction before the IRS contacted P. X's amended return would have been a qualified amended return if it was submitted prior to the date on which the IRS contacted P.
The facts are the same as in Example 3 except that, instead of contacting P concerning an examination under section 6707(a), in December 2004, the IRS served P with a John Doe summons described in section 7609(f) relating to the tax liability of participants in the type of transaction for which X claimed tax benefits on its return. X cannot file a qualified amended return after the John Doe summons has been served regardless of when, or whether, the transaction becomes a listed transaction.
On November 30, 2003, the IRS served a John Doe summons described in section 7609(f) on Corporation Y, a credit card company. The summons requested the identity of, and information concerning, United States taxpayers who, during the taxable years 2001 and 2002, had signature authority over Corporation Y's credit cards issued by, through, or on behalf of certain offshore financial institutions. Corporation Y complied with the summons, and identified, among others, Taxpayer B. On May 31, 2004, before the IRS first contacted Taxpayer B concerning an examination of Taxpayer B's Federal income tax return for the taxable year 2002, Taxpayer B filed an amended return for that taxable year, that showed an increase in Taxpayer B's Federal income tax liability. Under paragraph (c)(3)(i)(D) of this section, the amended return is not a qualified amended return because it was not filed before the John Doe summons was served on Corporation Y.
The facts are the same as in Example 5. Taxpayer B continued to maintain the offshore credit card account through 2003 and filed an original tax return for the 2003 taxable year claiming tax benefits attributable to the existence of the account. On March 21, 2005, Taxpayer B filed an amended return for the taxable year 2003, that showed an increase in Taxpayer B's Federal income tax liability. Under paragraph (c)(3)(i)(D) of this section, the amended return is not a qualified amended return because it was not filed before the John Doe summons for 2001 and 2002 was served on Corporation Y, and the return reflects benefits from the type of activity that is the subject of the John Doe summons.
(i) On November 30, 2003, the IRS served a John Doe summons described in section 7609(f) on Corporation Y, a credit card company. The summons requested the identity of, and information concerning, United States taxpayers who, during the taxable years 2001 and 2002, had signature authority over Corporation Y's credit cards issued by, through, or on behalf of certain offshore financial institutions. Taxpayer C did not have signature authority over any of Corporation Y's credit cards during either 2001 or 2002 and, therefore, was not a person described in the John Doe summons.
(ii) In 2003, Taxpayer C first acquired signature authority over a Corporation Y credit card issued by an offshore financial institution. Because Taxpayer C did not have signature authority during 2001 or 2002 over a Corporation Y credit card issued by an offshore financial institution, and was therefore not covered by the John Doe summons served on November 30, 2003, Taxpayer C's ability to file a qualified amended return for the 2003 taxable year is not limited by paragraph (c)(3)(i)(D) of this section.
Taxpayer's 1990 return showed a tax liability of $18,000. Taxpayer had no amounts previously assessed (or collected without assessment) and received no rebates of tax. Taxpayer claimed a credit in the amount of $23,000 for income tax withheld under section 3402, which resulted in a refund received of $5,000. It is later determined that the taxpayer should have reported additional income and that the correct tax for the taxable year is $25,500. There is an underpayment of $7,500, determined as follows:
| Tax imposed under subtitle A | $25,500 | |
| Tax shown on return | $18,000 | |
| Tax previously assessed (or collected without assessment) | None | |
| Amount of rebates made | None | |
| Balance | $18,000 | |
| Underpayment | $7,500 |
The facts are the same as in Example 1 except that the taxpayer failed to claim on the return a credit of $1,500 for income tax withheld. This $1,500 constitutes an amount collected without assessment as defined in paragraph (d) of this section. The underpayment is $6,000, determined as follows:
| Tax imposed under subtitle A | $25,500 | |
| Tax shown on return | $18,000 | |
| Tax previously assessed (or collected without assessment) | 1,500 | |
| Amount of rebates made | None | |
| Balance | $19,500 | |
| Underpayment | $6,000 |
On Form 1040 filed for tax year 1990, taxpayer reported a tax liability of $10,000, estimated tax payments of $15,000, and received a refund of $5,000. Estimated tax payments actually made with respect to tax year 1990 were only $7,000. For purposes of determining the amount of underpayment subject to a penalty under section 6662 or section 6663, the tax shown on the return is $2,000 (reported tax liability of $10,000 reduced by the overstated estimated tax of $8,000 ($15,000-$7,000)). The underpayment is $8,000, determined as follows:
| Tax imposed under subtitle A | $10,000 | |
| Tax shown on return | $2,000 | |
| Tax previously assessed (or collected without assessment) | None | |
| Amount of rebates made | None | |
| Balance | $2,000 | |
| Underpayment | $8,000 |
[T.D. 8381, 56 FR 67506, Dec. 31, 1991; T.D. 8381, 57 FR 6165, Feb. 20, 1992, as amended by T.D. 9186, 70 FR 10039, Mar. 2, 2005; T.D. 9309, 72 FR 903, Jan. 9, 2007]
Terms defined here
Where the text says “the term … means”. Select a term to jump to its definition.
Cross-references
Computed from the citations in the text of 26 CFR.
Code sections it cites
- § 6662 Imposition of accuracy-related penalty on underpayments
- § 6663 Imposition of fraud penalty
- § 31 Tax withheld on wages
- § 6851 Termination assessments of income tax
- § 6861 Jeopardy assessments of income, estate, gift, and certain excise taxes
- § 531 Imposition of accumulated earnings tax
- § 33 Tax withheld at source on nonresident aliens and foreign corporations
- § 6227 Administrative adjustment request by partnership
- § 6700 Promoting abusive tax shelters, etc.
- § 7609 Special procedures for third-party summonses
- § 6707 Failure to furnish information regarding reportable transactions
- § 6111 Disclosure of reportable transactions
- § 6112 Material advisors of reportable transactions must keep lists of advisees, etc.
- § 3402 Income tax collected at source
Regulations it cites
- § 1.6662-4 Substantial understatement of income tax.
- § 1.6011-4 Requirement of statement disclosing participation in certain transactions by taxpayers.
- § 1.6662-3 Negligence or disregard of rules or regulations.
- § 1.6664-4 Reasonable cause and good faith exception to section 6662 penalties.
Cited by 13 other regulations
- § 1.108-2 Acquisition of indebtedness by a person related to the debtor.
- § 1.482-1 Allocation of income and deductions among taxpayers.
- § 1.6011-10 Micro-captive listed transaction.
- § 1.6418-2 Rules for making transfer elections.
- § 1.6662-2 Accuracy-related penalty.
- § 1.6662-3 Negligence or disregard of rules or regulations.
- § 1.6662-4 Substantial understatement of income tax.
- § 1.6662-5 Substantial and gross valuation misstatements under chapter 1.
- § 1.6662-6 Transactions between persons described in section 482 and net section 482 transfer price adjustments.
- § 1.6664-0 Table of contents.
- § 1.6664-1 Accuracy-related and fraud penalties; definitions, effective date and special rules.
- § 301.6226-3 Adjustments taken into account by partners.
- § 301.9100-3 Other extensions.
Amendment history
From the source citation at the end of the section, newest first. T.D. is a Treasury decision; FR is the Federal Register.
- Amended by T.D. 9309 (72 FR 903)
- Amended by T.D. 9186 (70 FR 10039)
- Amended by T.D. 8381 (57 FR 6165)
- Issued by T.D. 8381 (56 FR 67506)
Where it sits in 26 CFR
- Subchapter A Income tax
- Part 1 Income taxes
- Additions to the tax, additional amounts, and assessable penalties
Nearby sections
- § 1.6662-7 Omnibus Budget Reconciliation Act of 1993 changes to the accuracy-related penalty.
- § 1.6662-9 Inconsistent estate basis reporting.
- § 1.6664-0 Table of contents.
- § 1.6664-1 Accuracy-related and fraud penalties; definitions, effective date and special rules.
- § 1.6664-2 Underpayment.
- § 1.6664-3 Ordering rules for determining the total amount of penalties imposed.
- § 1.6664-4 Reasonable cause and good faith exception to section 6662 penalties.
- § 1.6664-4T Reasonable cause and good faith exception to section 6662 penalties.
- § 1.6694-0 Table of contents.