Attribution rules
(iii) Attribution rules(A) In general. Except as otherwise provided in paragraph (j)(3)(iii)(B) of this section, a person's ownership percentage in a passthrough entity or in an undertaking shall be determined by treating such person as the owner of any interest that a person related to such person owns (determined without regard to this paragraph (j)(3)(iii)) in such passthrough entity or in such undertaking. (B) Determination of common-ownership percentage. The common-ownership percentage of five or fewer persons with respect to two or more undertakings shall be determined, in any case in which, after the application of paragraph (j)(3)(iii)(A) of this section, two or more such persons own the same interest in any such undertaking (the related-party owners) by treating as the only owner of such interest (or portion thereof) the related-party owner whose ownership of such interest (or a portion thereof) would result in the highest common-ownership percentage. (C) Related person. A person is related to another person for purposes of this paragraph (j)(3)(iii) if the relationship of such persons is described in section 267(b) or 707(b)(1). (4) Special rule for trade or business activities. In determining whether two or more trade or business activities are controlled by the same interests for purposes of paragraph (g) of this section, each such activity shall be treated as a separate undertaking in applying this paragraph (j). (5) Examples. The following examples illustrate the application of this paragraph (j):