(a) In general. Section 6662(a) and (b)(8) impose an accuracy-related penalty on the portion of any underpayment of tax required to be shown on an income tax return that is attributable to an inconsistent estate basis.

(b) Inconsistent estate basis—(1) In general. There is an inconsistent estate basis in property under section 6662(k) to the extent that a taxpayer claims a basis that was determined by using an initial basis as defined in § 1.1014-10(a)(2) that exceeds the property's final value as determined under § 1.1014-10(b)(1). The property to which this section applies is the property described in § 1.1014-10(c)(1).

(2) Example. The following example illustrates the provisions of paragraph (b)(1) of this section. In year 1, taxpayer (T), a citizen of the United States, inherited a house, property described in § 1.1014-10(c)(1) and not described in § 1.1014-10(c)(2). The final value and thus initial basis of the house as determined under § 1.1014-10(b) was $300,000. In year 5, T spent $85,000 on an addition to the house, which is added to T's initial basis in the house under section 1016(a). In year 11, T sold the house to an unrelated third party for $650,000. On T's return, T claims an initial basis of $400,000 and the $85,000 spent on the addition to the house, for a total claimed basis of $485,000. T's claimed initial basis exceeds the allowable basis by $100,000. Because this amount is due to T claiming an initial basis as defined in § 1.1014-10(a)(2) that exceeds the property's final value as determined under § 1.1014-10(b), T is liable for the 20% accuracy-related penalty for the portion of any underpayment that is attributable to the reporting of an inconsistent basis.

(c) Applicability date. This section applies to property described in § 1.1014-10(c)(1) that is reported on an estate tax return required under section 6018 that is filed after September 17, 2024.