; and (2) by inserting after subsection (b) the following new subsection: (c) Additional tax for old-Age, survivors, and disability insurance (1) In general In addition to the taxes imposed by the preceding subsections, there is hereby imposed on every individual for each taxable year beginning after December 31, 2018, a tax equal to 4 percent of additional self-employment income for such taxable year. (2) Additional self-employment income For purposes of paragraph (1), the term additional self-employment income means, for any taxable year, the amount (not less than zero) equal to the excess of— (A) the sum of self-employment income (determined without regard to section 1402(b)(1)) for the taxable year and wages (as defined in section 3121(a), determined without regard to paragraph (1) thereof) paid to such individual during such taxable year, over (B) the sum of the additional wages (as defined in section 3101(c)(2)) paid to such individual for the taxable year and the amount determined under paragraph (3) for the taxable year. Rules similar to the rules of subparagraph (A) of the second sentence of section 1402(b) shall apply for purposes of determining wages under clause (i). (3) Exemption amount The amount determined under this paragraph is an amount equal to— (A) in the case of a taxable year beginning after December 31, 2018, and before January 1, 2020, $400,000, and (B) in the case of any taxable year beginning after December 31, 2019, the product of— (i) $400,000, and (ii) the quotient obtained by dividing— (I) the national average wage index (as defined in section 209(k)(1)) for the calendar year which is 2 years before the calendar year in which the taxable year begins, by (II) the national average wage index for calendar year 2017. . (b) Employee wage surtax Section 3101 of the Internal Revenue Code of 1986 is amended— (1) by redesignating subsection (c) as subsection (d)