Which form must be timely filed to complete the portability election for the deceased spousal unused exclusion?

The correct form for completing the portability election for the deceased spousal unused exclusion is Form 706. This form is the United States Estate (and Generation-Skipping Transfer) Tax Return, which is specifically designed to address the federal estate tax. When a decedent’s estate qualifies for portability, filing Form 706 is necessary to elect portability of the deceased spousal unused exclusion amount to the surviving spouse.

The portability election allows the surviving spouse to use the unused portion of the deceased spouse's estate tax exclusion, which can significantly benefit the surviving spouse's estate planning by increasing the amount that can pass tax-free upon their death. Timely filing this form is crucial as it must be done within nine months of the spouse's death to preserve this benefit, unless an extension has been granted.

Filing forms like Form 1040 or Form 1041 would not specifically address the portability election as they relate to income tax returns for individuals and estates, respectively, rather than estate tax and the election of portability. A notarized written statement does not suffice for this election either, as the IRS requires the formal submission of Form 706 itself to finalize the portability claim.