Replaces paragraph (1) of subsection (a) of 26 U.S.C. 2513 with a new, gender-neutral paragraph that retains the one-half attribution rule for gifts by one spouse to third parties (subject to the U.S. citizen/resident limitation), preserves the exception for gifts that create a general power of appointment in the spouse, and clarifies the definition of spouse for purposes of the section (must be married at the time of the gift and not remarry during the remainder of the calendar year).

Provides that an individual first treated as married by application of Revenue Ruling 2013–17 who filed a return (other than a joint return) for a taxable year ending before September 16, 2013, for which a joint return could have been made, shall be treated as having filed a separate return within the meaning of section 6013(b), and prevents the time in section 6013(b)(2)(A) for filing a joint return after filing a separate return from expiring before the filing deadline (including extensions) for the taxable year that includes the date of enactment.

Extends the period of limitation prescribed by section 6511(a) for taxable years covered by a joint return filed pursuant to the treatment in subsection (a)(1) until the filing deadline (including extensions) for the taxable year that includes the date of enactment of this Act.

Provides that section 6511(b)(2) shall not apply to any claim for credit or refund with respect to a joint return filed pursuant to the treatment in subsection (a)(1).

Makes numerous amendments to the Internal Revenue Code of 1986 by striking specified words or phrases and inserting replacement text as enumerated in section 4. Sections and subsections explicitly identified for amendment in subsection (a) include: 1(a)(1), 1(d); 2(b)(2)(A); 21(d)(1)(B), 21(e)(3); 36(c)(5); 179(d)(2)(A); 318(a)(1)(A)(i); 408(d)(6); 469(i)(5)(B)(ii); 507(d)(2)(B)(iii); 613A(c)(8)(D)(ii) and (iii); 672(e)(2); 704(e)(2); 911(c)(3)(subparagraphs (A) and (B)(ii)); 1235(c)(2); 1563(e)(5); 3121(b)(3)(B); 4946(d); 4975(e)(6); 6012(a)(1)(subparagraphs (A)(iv) and (B)); and 7703(a)(paragraphs (1) and (2)). Subsection (b) lists additional conforming amendments to numerous sections (including, among others, 2(a)(2)(B); 2(b)(1) and 2(b)(2); 21(e) provisions; 36B(e)(1); 63(e) and 63(f); 86(c)(1)(C)(ii); 105(c)(1); 119 provisions; 129(b)(2); 151(b); 170(b)(1)(F)(iii); 2012(c); 2032A(e)(10); 2035(b); 2056(a) and 2056(b)(5); 2523 provisions; 3121(b)(3); 3306(c)(5); 3402(l); 4905(a); 6046(c); 6103(e)(1)(A)(ii); 7448 provisions). Subsection (b)(6) specifies targeted textual substitutions in a long list of individual Code provisions (for example: in section 2(a)(1)(A) replace “his two taxable years” with “the taxpayer's two taxable years”; in section 2(a)(1)(B) replace “his home” with “the taxpayer's home”; and many similar replacements across sections cited). See the section text for the full enumerated list of the specific subsection-level amendments and exact wording replaced/inserted.