Section 301.6221(a)-1 - Determination at partnership level(a)In general. Except as otherwise provided under subchapter C of chapter 63 of the Internal Revenue Code (subchapter C of chapter 63) and the regulations in this part, any adjustment to a partnership-related item (as defined in § 301.6241-1(a)(6)(ii) ) is determined, any tax imposed by chapter 1 of the Internal Revenue Code (Code) attributable thereto is assessed and collected, and the applicability of any penalty, addition to tax, or additional amount that relates to an adjustment to any partnership-related item is determined at the partnership level under subchapter C of chapter 63.(b)Legal and factual determinations at the partnership level. Except as otherwise provided under subchapter C of chapter 63, any legal or factual determinations underlying any adjustment or determination made in accordance with paragraph (a) of this section are also determined at the partnership level under subchapter C of chapter 63. For instance, determinations under this paragraph (b) include any determinations necessary to calculate the imputed underpayment or any modification of the imputed underpayment under section 6225 and the period of limitations on making adjustments under subchapter C of chapter 63.(c)Applicability date - (1)In general. Except as provided in paragraph (c)(2) of this section, this section applies to partnership taxable years beginning after December 31, 2017, and ending after August 12, 2018.(2)Election under § 301.9100-22 in effect. This section applies to any partnership taxable year beginning after November 2, 2015, and before January 1, 2018, for which a valid election under § 301.9100-22 is in effect.T.D. 9844, 84 FR 6531 , Feb. 27, 2019 T.D. 9844, 84 FR 6531, 2/27/2019