26 U.S.C. § 1411: Imposition of tax

net investment income for such taxable year, or the modified adjusted gross income for such taxable year, over the threshold amount. the undistributed net investment income for such taxable year, or the adjusted gross income (as defined in section 67(e)) for such taxable year, over the dollar amount at which the highest tax bracket in section 1(e) begins for such taxable year. in the case of a taxpayer making a joint return under section 6013 or a surviving spouse (as defined in section 2(a)), $250,000, in the case of a married taxpayer (as defined in section 7703) filing a separate return, ½ of the dollar amount determined under paragraph (1), and in any other case, $200,000. gross income from interest, dividends, annuities, royalties, and rents, other than such income which is derived in the ordinary course of a trade or business not described in paragraph (2), other gross income derived from a trade or business described in paragraph (2), and net gain (to the extent taken into account in computing taxable income) attributable to the disposition of property other than property held in a trade or business not described in paragraph (2), over the deductions allowed by this subtitle which are properly allocable to such gross income or net gain. a passive activity (within the meaning of section 469) with respect to the taxpayer, or a trade or business of trading in financial instruments or commodities (as defined in section 475(e)(2)). A rule similar to the rule of section 469(e)(1)(B) shall apply for purposes of this subsection. gain from such disposition shall be taken into account under clause (iii) of paragraph (1)(A) only to the extent of the net gain which would be so taken into account by the transferor if all property of the partnership or S corporation were sold for fair market value immediately before the disposition of such interest, and a rule similar to the rule of subparagraph (A) shall apply to a loss from such disposition. The term “net investment income” shall not include any distribution from a plan or arrangement described in section 401(a), 403(a), 403(b), 408, 408A, or 457(b). Net investment income shall not include any item taken into account in determining self-employment income for such taxable year on which a tax is imposed by section 1401(b). the amount excluded from gross income under section 911(a)(1), over the amount of any deductions (taken into account in computing adjusted gross income) or exclusions disallowed under section 911(d)(6) with respect to the amounts described in paragraph (1). a nonresident alien, or a trust all of the unexpired interests in which are devoted to one or more of the purposes described in section 170(c)(2)(B).