(1) Negligence or disregard of rules or regulations (see § 1.6662-3);

(2) Any substantial understatement of income tax (see § 1.6662-4); or

(3) Any substantial (or gross) valuation misstatement under chapter 1 (“substantial valuation misstatement” or “gross valuation misstatement”), provided the applicable dollar limitation set forth in section 6662(e)(2) is satisfied (see § 1.6662-5).

(1) In general. The amount of the accuracy-related penalty is 20 percent of the portion of an underpayment of tax required to be shown on a return that is attributable to any of the types of misconduct listed in paragraphs (a)(1) through (a)(3) of this section, except as provided in paragraph (b)(2) of this section.

(2) Increase in penalty for gross valuation misstatement. In the case of a gross valuation misstatement, as defined in section 6662(h)(2) and § 1.6662-5(e)(2), the amount of the accuracy-related penalty is 40 percent of the portion of an underpayment of tax required to be shown on a return that is attributable to the gross valuation misstatement, provided the applicable dollar limitation set forth in section 6662(e)(2) is satisfied.

(1) Returns due before January 1, 1994. Section 1.6662-3(c) and §§ 1.6662-4 (e) and (f) (relating to methods of making adequate disclosure) (as contained in 26 CFR part 1 revised April 1, 1995) apply to returns the due date of which (determined without regard to extensions of time for filing) is after December 31, 1991, but before January 1, 1994. Except as provided in the preceding sentence and in paragraphs (d)(2), (3), and (4) of this section, §§ 1.6662-1 through 1.6662-5 apply to returns the due date of which (determined without regard to extensions of time for filing) is after December 31, 1989, but before January 1, 1994. To the extent the provisions of these regulations were not reflected in the statute as amended by the Omnibus Budget Reconciliation Act of 1989 (OBRA 1989), in Notice 90-20, 1990-1 C.B. 328, or in rules and regulations in effect prior to March 4, 1991 (to the extent not inconsistent with the statute as amended by OBRA 1989), these regulations will not be adversely applied to a taxpayer who took a position based upon such prior rules on a return filed before January 1, 1992.

(2) Returns due after December 31, 1993. Except as provided in paragraphs (d)(3), (4) and (5) of this section and the last sentence of this paragraph (d)(2), the provisions of §§ 1.6662-1 through 1.6662-4 and § 1.6662-7 (as revised to reflect the changes made to the accuracy-related penalty by the Omnibus Budget Reconciliation Act of 1993) and of § 1.6662-5 apply to returns the due date of which (determined without regard to extensions of time for filing) is after December 31, 1993. These changes include raising the disclosure standard for the penalties for disregarding rules or regulations and for a substantial understatement of income tax from not frivolous to reasonable basis, eliminating the disclosure exception for the negligence penalty, and providing guidance on the meaning of reasonable basis. The Omnibus Budget Reconciliation Act of 1993 changes relating to the penalties for negligence or disregard of rules or regulations will not apply to returns (including qualified amended returns) that are filed on or before March 14, 1994, but the provisions of §§ 1.6662-1 through 1.6662-3 (as contained in 26 CFR part 1 revised April 1, 1995) relating to those penalties will apply to such returns.

(3) Special rules for tax shelter items. Sections 1.6662-4(g)(1) and 1.6662-4(g)(4) apply to returns the due date of which (determined without regard to extensions of time for filing) is after September 1, 1995. Except as provided in the last sentence of this paragraph (d)(3), §§ 1.6662-4(g)(1) and 1.6662-4(g)(4) (as contained in 26 CFR part 1 revised April 1, 1995) apply to returns the due date of which (determined without regard to extensions of time for filing) is on or before September 1, 1995 and after December 31, 1989. For transactions occurring after December 8, 1994, §§ 1.6662-4(g)(1) and 1.6662-4(g)(2) (as contained in 26 CFR part 1 revised April 1, 1995) are applied taking into account the changes made to section 6662(d)(2)(C) (relating to the substantial understatement penalty for tax shelter items of corporations) by section 744 of title VII of the Uruguay Round Agreements Act, Pub. L. 103-465 (108 Stat. 4809).

(4) Special rules for reasonable basis. Section 1.6662-3(b)(3) applies to returns filed on or after December 2, 1998.

(5) For returns filed after December 31, 2002. Sections 1.6662-3(a), 1.6662-3(b)(2) and 1.6662-3(c)(1) (relating to adequate disclosure) apply to returns filed after December 31, 2002, with respect to transactions entered into on or after January 1, 2003. Except as provided in paragraph (d)(1) of this section, §§ 1.6662-3(a), 1.6662-3(b)(2) and 1.6662-3(c)(1) (as contained in 26 CFR part 1 revised April 1, 2003) apply to returns filed with respect to transactions entered into prior to January 1, 2003.