A US citizen or green-card holder married to a non-US citizen who is not a US resident for tax purposes faces a filing decision most married couples never encounter. The default is Married Filing Separately (MFS). The main alternative is a formal election under Internal Revenue Code §6013(g) or §6013(h) to treat the nonresident-alien spouse as a US resident for the year, which unlocks joint (MFJ) rates and the larger standard deduction but pulls the spouse's worldwide income and foreign-asset reporting into the US net. A third path, Head of Household (HOH), is available in narrower circumstances. Which path minimises the family's total tax bill turns less on nominal rates than on where the couple lives, how much the foreign spouse earns, whether joint accounts exist, and whether the household plans to remain abroad or return to the US.
This article walks through the three paths, the ITIN process required to file with any nonresident-alien spouse, the situations in which the joint-filing election helps versus backfires, and the joint-account reporting exposure that catches most couples off guard. Rules cited are current as of 2026; the interaction of US tax law with any specific foreign regime should be verified with a cross-border adviser before filing.
The three filing paths at a glance
| Path | NRA spouse's foreign income | 2026 standard deduction | Reporting exposure | Typical best fit |
|---|---|---|---|---|
| MFS (default) | Not taxed by the US | $16,100 | Only the US person's accounts | NRA spouse earns or holds meaningful foreign assets |
| §6013(g) MFJ election | Fully taxable in the US | $32,200 | Both spouses' worldwide accounts | NRA spouse earns little; couple lives in the US |
| Head of Household | Not taxed by the US | Between MFS and MFJ (verify current IRS figure) | Only the US person's accounts | US spouse has a qualifying child dependent; NRA spouse does not elect residency |
The Single/MFS and MFJ standard-deduction figures come from the IRS 2026 inflation adjustments and are reflected in the United States country profile. The US federal system remains progressive from 10% to 37% (the seven-bracket TCJA structure was made permanent by the One Big Beautiful Bill Act signed 4 July 2025), and citizenship-based taxation still applies — meaning the US person's worldwide income is on the return regardless of where the couple lives.
Why MFS is the statutory default
Under US tax law, a person married on the last day of the year files either MFJ or MFS. If a US citizen or resident is married to a nonresident alien and no §6013(g) election is on file, the couple is not eligible to file jointly. The US spouse defaults into MFS. The NRA spouse has no US filing obligation on foreign-source income and is not required to obtain an ITIN unless they have US-source income of their own.
MFS has three cost centres worth being blunt about. First, the brackets compress faster than MFJ, so a US spouse with a strong salary hits higher marginal rates sooner. Second, a long list of credits and deductions is disallowed or phased out at low income under MFS, including the American Opportunity credit at full value, the student-loan interest deduction, the traditional-IRA deduction if the spouse is covered by a workplace plan, and — in most fact patterns — the Earned Income Tax Credit. Third, if either spouse itemises, the other must itemise too; this is rarely an issue when the NRA spouse has no US filing, but becomes relevant if that spouse later has US-source income.
What MFS preserves is the ring-fence around the NRA spouse. Their foreign salary, foreign business profits, foreign pension accruals, and foreign investment income sit outside the US tax return and outside US information reporting. In many cross-border marriages, that ring-fence is worth far more than the deduction and credit uplift that MFJ would deliver.
The §6013(g) election: joint filing at a cost
A US citizen or resident married to a nonresident alien can jointly elect, in writing, to have the NRA spouse treated as a US resident for the entire year. §6013(g) covers ongoing marriages; §6013(h) covers the first-year election when the NRA spouse becomes a US resident mid-year. The election is filed by attaching a signed statement to the joint return the first year it applies. Once made, it stays in force for every subsequent year until one spouse formally revokes it, the marriage ends, or death or expatriation intervenes. Revocation is available, but once revoked the same couple can never make the election again.
The benefits are mechanical: MFJ brackets, the larger standard deduction ($32,200 for 2026), full access to credits and deductions that MFS disallows, and — for expat couples — the ability of each spouse to claim their own Foreign Earned Income Exclusion (up to $132,900 per spouse for 2026, per the US profile) against their own foreign earned income. Foreign tax credits offset foreign taxes paid on the same income stream. The FEIE-versus-FTC choice now has to be run twice, once for each spouse.
The costs are structural. From the moment the election is on file, the NRA spouse is a US resident for income-tax purposes. Their worldwide income is taxable in the US: foreign salary, foreign self-employment profit, foreign rental income, foreign dividends and interest, foreign capital gains, foreign pension accruals under IRS characterisation, everything. They are equally subject to US information reporting: FBAR (FinCEN 114) on foreign accounts they own or co-own, Form 8938 (FATCA) if their share of foreign financial assets pushes the household above the threshold, Form 8621 for any holdings that meet the passive foreign investment company (PFIC) definition, and Form 3520 for gifts from non-US persons above the annual threshold. See the FBAR and FATCA guide for the specifics, and the PFIC rules explainer for why non-US mutual funds and unit trusts are so punitive on a US return.
The ITIN process (Form W-7)
An NRA spouse with no Social Security Number needs an Individual Taxpayer Identification Number (ITIN) to appear on any US return — MFS with the NRA spouse's name shown as "NRA" is an option, but as soon as an election is made or the spouse claims any US benefit, an ITIN is required. Form W-7 is filed with the first return that uses it, not separately.
The mechanics that trip most couples up:
- Original identity documents or copies certified by the issuing authority are required. Regular notarised copies are not accepted.
- A passport is the only stand-alone document the IRS accepts. Anything else requires two documents.
- Mailing original passports to Austin, Texas is a non-starter for most families. The workarounds are either an in-person appointment at an IRS Taxpayer Assistance Center or a Certifying Acceptance Agent (CAA), who can verify documents locally.
- Processing times run several weeks to several months. Couples electing §6013(g) or §6013(h) for the first time should build ITIN issuance into their filing timeline rather than assume a normal April deadline works.
When the election helps
The §6013(g) election tends to be the right answer in three fact patterns. First, when the NRA spouse has little or no independent income — a stay-at-home parent, a student, or a spouse whose earnings sit under a modest threshold. The joint standard deduction and wider brackets absorb the US spouse's income more efficiently, and there is little foreign income being newly exposed. Second, when the couple lives in the US and the NRA spouse is on a visa that already generates US-source income; in that case, the residency question is largely moot and the election just cleans up the filing status. Third, when access to a specific credit (child- or education-related, most commonly) meaningfully exceeds the incremental tax on the spouse's small foreign income.
The election also simplifies life for couples planning to relocate to the US within a year or two. Making the election early and running one integrated return is cleaner than switching filing status back and forth as residency changes.
When the election backfires
The election tends to be the wrong answer whenever the NRA spouse has substantial foreign income, foreign assets, or both, and the couple has no plan to move to the US.
A concrete illustration using Thailand: since January 2024, all foreign income remitted to Thailand is taxable there regardless of when it was earned (see the Thailand profile and the 2026 Thailand guide). A Thai citizen spouse earning a Thai salary of, say, THB 3,000,000 pays Thai tax on the local progressive schedule up to 35%. If the US spouse elects §6013(g), that Thai salary becomes US-taxable as well. The FEIE can shelter the first $132,900 per spouse, and foreign tax credits reduce further exposure, but the paperwork burden — FBAR on the spouse's Thai bank accounts, Form 8938 exposure, PFIC screening on any Thai mutual funds — is real and permanent. The election also means the Thai spouse is on the hook for a US return every year for the rest of the marriage.
A parallel case in Mexico: a Mexican citizen spouse is already taxed on worldwide income at progressive rates up to 35% once tax-resident under the 183-day or centre-of-vital-interests test (see the Mexico profile and the Mexico expat guide). Layering a US return on top rarely produces net US tax after foreign tax credits — Mexico's rates are close to US rates — but it does add years of US filings, opens the spouse's Mexican brokerage accounts to reporting, and can create PFIC drag if any of those accounts hold Mexican mutual funds or ETFs.
In both cases, MFS keeps the ring-fence intact. The US spouse files their own return; the NRA spouse's Thai or Mexican financial life stays outside the US system.
Head of Household as an escape valve
A US citizen or resident married to a nonresident alien is treated as "considered unmarried" for HOH purposes if they do not elect §6013(g) or §6013(h). That opens Head of Household eligibility, which requires a qualifying child (or in narrower cases, a qualifying relative) who lived with the US spouse for more than half the year and for whom the US spouse paid more than half the cost of maintaining the home.
HOH sits between MFS and MFJ on both the standard deduction and the bracket structure — the exact 2026 figure should be pulled from the IRS release, but it is meaningfully more generous than MFS. It also restores access to a number of the credits MFS phases out. For a US-citizen parent living abroad with a US-citizen child while married to a foreign national, HOH is often the single biggest filing improvement available without triggering the reporting cascade of the §6013(g) election.
Joint accounts and the reporting cliff
Even with MFS, a US spouse who is a signatory on, or joint owner of, a foreign account with the NRA spouse is on the hook for reporting that account. FBAR filing thresholds are triggered by aggregate foreign account balances over $10,000 at any point in the year — the fact that half the balance economically belongs to the foreign spouse does not matter for reporting purposes. Form 8938 thresholds are higher and vary depending on whether the US spouse lives inside or outside the US, but the same principle applies: a joint account is a reportable account.
Two practical consequences follow. First, couples who care about keeping the NRA spouse's finances outside the US reporting system usually keep separate accounts, not joint ones, and are careful about signature authority. Second, if joint accounts already exist, the US spouse should file the FBAR reflecting them; "quiet" non-filing is riskier than a straightforward filing, and the Streamlined Filing Compliance Procedures exist for exactly the couples who discover the requirement late.
Estate and gift tax: the citizenship line
The unlimited marital deduction — the ability to transfer assets between spouses in life or at death with no US estate or gift tax — applies only to transfers to a US citizen spouse. Transfers to a non-citizen spouse are limited. The US person can rely on the general lifetime estate and gift exemption (raised by the OBBBA to $15M per individual and $30M per couple for 2026, per the US profile) for transfers above the annual exclusion, but the exclusion itself is inflation-indexed and materially larger for gifts to a non-citizen spouse than the standard annual exclusion between US persons. The precise 2026 figure should be verified with a preparer before making planned gifts.
At death, transfers to a non-citizen surviving spouse do not qualify for the unlimited marital deduction, which can accelerate estate tax that would otherwise be deferred. The standard workaround is a Qualified Domestic Trust (QDOT), which allows the marital deduction on the estate return in exchange for holding the assets in a trust that ensures eventual US estate tax collection. QDOTs are a planning tool, not a filing checkbox — a couple with meaningful assets and a non-citizen spouse should build the QDOT question into their estate plan rather than discover it during probate.
Country-specific interactions worth knowing
Two treaty and residency points regularly reshape the analysis. First, the US–Mexico income tax treaty prevents double taxation but does not override citizenship-based taxation for the US spouse. It shapes credit ordering and withholding, not the fundamental filing obligation. Second, for a US spouse who has become tax-resident in Thailand under the 180-day rule, the remittance-basis change effective January 2024 means that money flowed into Thailand — including salary, distributions, or investment proceeds — is Thai-taxable. Couples running their finances through a joint Thai account after moving there should model the Thai side and the US side together, not sequentially.
For US citizens considering leaving the US net entirely, the renunciation guide and the exit-tax explainer cover the exit tax and covered-expatriate rules that intersect with any long-term filing plan. For couples in the ordinary case — staying married, staying abroad, staying compliant — the choice is usually MFS with careful account segregation, HOH if a qualifying child is available, and the §6013(g) election reserved for the narrow set of families where it clearly pencils out.
Where to go next
For related TaxAtlas research, see the United States country profile, the Thailand and Mexico profiles, the 2026 guide for US citizens moving abroad, the FBAR and FATCA guide, and the how tax residency works and tax treaties explainers. The country comparison tool and the FAQ cover the personal-tax fundamentals across all 46 tracked jurisdictions.