Yes—you can generally amend your 2023 separate return to file jointly now, provided you qualify for joint filing or a cross-border election and meet both the amendment and refund deadlines.

§6013(a)

A husband and wife may make a single return jointly of income taxes under subtitle A, even though one of the spouses has neither gross income nor deductions, except as provided below:

§6013(a)(1)

(1) no joint return shall be made if either the husband or wife at any time during the taxable year is a nonresident alien;

§6013(b)(1)

Except as provided in paragraph (2), if an individual has filed a separate return for a taxable year for which a joint return could have been made by him and his spouse under subsection (a) and the time prescribed by law for filing the return for such taxable year has expired, such individual and his spouse may nevertheless make a joint return for such taxable year.

§6013(b)(2)(A)

(A) after the expiration of 3 years from the last date prescribed by law for filing the return for such taxable year (determined without regard to any extension of time granted to either spouse);

When To File

File Form 1040 or 1040-SR by April 15, 2024.

§6511(a)

Claim for credit or refund of an overpayment of any tax imposed by this title in respect of which tax the taxpayer is required to file a return shall be filed by the taxpayer within 3 years from the time the return was filed or 2 years from the time the tax was paid, whichever of such periods expires the later, or if no return was filed by the taxpayer, within 2 years from the time the tax was paid.

§6013(g)

This subsection shall be in effect with respect to any individual who, at the close of the taxable year for which an election under this subsection was made, was a nonresident alien individual married to a citizen or resident of the United States, if both of them made such election to have the benefits of this subsection apply to them.

Nonresident Spouse Treated as a Resident

However, you can also make the choice by filing a joint amended return on Form 1040-X.

Nonresident Spouse Treated as a Resident

Attach a statement, signed by both spouses, to your joint return for the first tax year for which the choice applies.

§1.6013-7(a)

Two individuals who are husband and wife at the close of a taxable year ending on or after December 31, 1975, may make an election under this section for that taxable year if one spouse is a citizen or resident of the United States on the last day of that taxable year and the other spouse is a nonresident alien at the beginning of that taxable year and a citizen or resident of the United States at the close of that taxable year.

Effect of the choice

Each spouse must report their entire worldwide income for the year you make the choice and for all later years unless the choice is ended or suspended.

How to make the choice

If you make the choice with an amended return, you and your spouse must also amend any returns that you may have filed after the year for which you made the choice.

First-Year Choice

Be present in the United States for at least 75% of the number of days beginning with the first day of the 31-day period and ending with the last day of 2023.

Changing From Separate to Joint Return

Both of you must sign and date Form 1040-X.

Assembling Your Paper Return

You must place behind your completed paper-filed Form 1040-X a completed and updated Form 1040, 1040-SR, or 1040-NR with the changes you are submitting.

Electronic filing

If amending a prior year return originally filed on paper, then the amended return must also be filed on paper.

Supporting documentation

You must submit original documents, or certified copies of these documents from the issuing agency, that support the information provided on Form W-7.

§6013(d)(3)

(3) if a joint return is made, the tax shall be computed on the aggregate income and the liability with respect to the tax shall be joint and several.