Code of Federal Regulations Title 26. Internal Revenue § 26.20.2056(a)–1 Marital deduction;  in general

(b) Requirements for marital deduction—(1) In general. To obtain the marital deduction with respect to any property interest, the executor must establish the following facts—

(2) Burden of establishing requisite facts. The executor must provide the facts relating to any applicable limitation on the amount of the allowable marital deduction under § 20.2056(a)–1(c), and must submit proof necessary to establish any fact required under paragraph (b)(1), including any evidence requested by the district director.

(c) Marital deduction;  limitation on aggregate deductions—(1) Estates of decedents dying before 1977. In the case of estates of decedents dying before January 1, 1977, the marital deduction is limited to one-half of the value of the adjusted gross estate, as that term was defined under section 2056(c)(2) prior to repeal by the Economic Recovery Tax Act of 1981.

(2) Estates of decedents dying after December 31, 1976, and before January 1, 1982—Except as provided in § 2002(d)(1) of the Tax Reform Act of 1976 (Pub. L. 94–455), in the case of decedents dying after December 31, 1976, and before January 1, 1982, the marital deduction is limited to the greater of—

(3) Estates of decedents dying after December 31, 1981. In the case of estates of decedents dying after December 31, 1981, the marital deduction is limited as prescribed in paragraph (c)(2) of this section if the provisions of § 403(e)(3) of Pub. L. 97–34 are satisfied.