applicable amount for each taxable year shall be an amount equal to the quotient obtained by dividing— (i) the amount described in paragraph (1)(A) for the calendar year in which such taxable year ends, by (ii) the amount described in paragraph (1)(B) for such taxable year. (B) Rounding Any amount determined under subparagraph (A) shall be rounded down to the next whole dollar amount. (3) Special rule In the case of any taxable year beginning after December 31, 2018, and ending before January 1, 2020, the amount under paragraph (2)(A)(i) shall be equal to the sum of the amounts determined under paragraph (1)(A) for calendar years 2018 and 2019. . (b) Conforming amendments (1) The table of sections for subpart C of part IV of subchapter A of chapter 1 of subtitle A of the Internal Revenue Code of 1986 is amended by inserting after the item relating to section 36B the following: Sec. 36C. Tariff rebate credit. . (2) Section 6211(b)(4)(A) of such Code is amended by striking and 36B, 168(k)(4) and inserting 36B, and 36C . (3) Paragraph (2) of section 1324(b) of title 31, United States Code, is amended by inserting 36C, after 36B, . (c) Authorization of appropriations There are authorized to be appropriated such sums as may be necessary to administer section 36C of the Internal Revenue Code of 1986 (as added by subsection (a)). (d) Effective date The amendments made by this section shall apply to taxable years beginning after December 31, 2018.