26 CFR § 20.2056A-3 - QDOT election.
(a) General rule. Subject to the time period prescribed in section 2056A(d), the election to treat a trust as a QDOT must be made on the last federal estate tax return filed before the due date (including extensions of time to file actually granted) or, if a timely return is not filed, on the first federal estate tax return filed after the due date. The election, once made, is irrevocable.
(b) No partial elections. An election to treat a trust as a QDOT may not be made with respect to a specific portion of an entire trust that would otherwise qualify for the marital deduction but for the application of section 2056(d). However, if the trust is actually severed in accordance with the applicable requirements of § 20.2056(b)-7(b)(2)(ii) prior to the due date for the election, a QDOT election may be made for any one or more of the severed trusts.
(c) Protective elections. A protective election may be made to treat a trust as a QDOT only if at the time the federal estate tax return is filed, the executor of the decedent's estate reasonably believes that there is a bona fide issue that concerns either the residency or citizenship of the decedent, the citizenship of the surviving spouse, whether an asset is includible in the decedent's gross estate, or the amount or nature of the property the surviving spouse is entitled to receive. For example, if at the time the federal estate tax return is filed either the estate is involved in a bona fide will contest, there is uncertainty regarding the inclusion in the gross estate of an asset which, if includible, would be eligible for the QDOT election, or there is uncertainty regarding the status of the decedent as a resident alien or a nonresident alien for estate tax purposes, or a similar uncertainty regarding the citizenship status of the surviving spouse, a protective QDOT election may be made. The protective election is in addition to, and is not in lieu of, the requirements set forth in § 20.2056A-4. The protective QDOT election must be made on a written statement signed by the executor under penalties of perjury and must be attached to the return described in paragraph (a) of this section, and must identify the specific assets to which the protective election refers and the specific basis for the protective election. However, the protective election may otherwise be defined by means of a formula (such as the minimum amount necessary to reduce the estate tax to zero). Once made, the protective election is irrevocable. For example, if a protective election is made because a bona fide question exists as to the includibility of an asset in the decedent's gross estate and it is later finally determined that the asset is so includible, the protective election becomes effective with respect to the asset and cannot thereafter be revoked.
(d) Manner of election. The QDOT election under paragraph (a) of this section is made in the form and manner set forth in the decedent's estate tax return, including applicable instructions.