ITIN vs. SSN: which tax ID do you need?

Every person reported on a U.S. tax return needs a U.S. taxpayer identification number — but not everyone is eligible for a Social Security Number. The Individual Taxpayer Identification Number (ITIN) exists for people who have U.S. tax obligations but can't get an SSN: typically foreign spouses, foreign-citizen dependents, and non-resident aliens with U.S. income.

For expat families, the ITIN-vs-SSN distinction often determines which tax benefits apply. This article covers when you need which, and how to get one.

SSN: who's eligible

A Social Security Number is issued to:

• U.S. citizens (by birth or naturalization)
• Lawful permanent residents (green-card holders)
• Other lawfully present non-citizens authorized to work in the U.S. (certain visa categories)

Notably, a non-U.S. spouse of a U.S. citizen does not automatically qualify for an SSN just because they're married to one — unless they've also obtained work authorization or a green card.

Children born abroad to U.S.-citizen parents are U.S. citizens automatically (subject to the parent's physical-presence-in-the-U.S. requirements) and qualify for SSNs through the U.S. embassy.

ITIN: who needs one

An ITIN is issued to individuals who have U.S. federal tax filing obligations but who are not eligible for an SSN. The most common situations for expat families:

1. A non-U.S. spouse of a U.S. citizen who files jointly with the U.S.-citizen spouse. Filing MFJ requires both spouses to have a U.S. tax ID; the foreign spouse gets an ITIN.
2. Foreign-citizen children of an expat family who are claimed as dependents. If the child is a foreign citizen (not U.S.) but lives with you and qualifies as a dependent — possible in some mixed-citizenship families — the child needs an ITIN.
3. Non-resident aliens with U.S.-source income (rare in the expat-family scenario, more common for foreign investors in U.S. real estate or U.S. stocks).
4. Dependents who must be reported on a U.S. return for one of several specific tax benefits.

If your dependent or spouse is a U.S. citizen (e.g., your kids born abroad with CRBA-confirmed citizenship), they need an SSN, not an ITIN. ITIN is the substitute for people who can't get an SSN.

What ITIN holders cannot claim

An ITIN exists for tax filing — it does not confer immigration status, work authorization, or eligibility for most U.S. benefits. Critically:

• Child Tax Credit (CTC): requires a child with a valid SSN. An ITIN-holding child does not qualify for the $2,000 CTC, only the $500 Credit for Other Dependents.
• Earned Income Tax Credit (EITC): requires SSN for the taxpayer, spouse (if MFJ), and any qualifying children. Even one ITIN in the family disqualifies the entire EITC.
• Social Security retirement / disability benefits: built on SSN contribution history.

This is the reason that registering your foreign-born U.S.-citizen child with the U.S. embassy and obtaining their SSN as soon as possible matters: every year delayed is a year without CTC eligibility.

How to get an SSN abroad

For a U.S.-citizen child born abroad:

1. Consular Report of Birth Abroad (CRBA) at a U.S. embassy or consulate. This officially documents the child's U.S. citizenship.
2. Apply for the SSN at the same appointment or shortly after — most embassies process SSA applications. The form is SS-5.
3. Receive the SSN by mail at your address on file. Allow several weeks to months in some countries.

For an adult U.S. citizen who never got an SSN (rare):

• Apply at any U.S. Social Security Administration office. If you're abroad, apply through the U.S. embassy.
• Provide proof of citizenship (passport, birth certificate, naturalization certificate).

How to get an ITIN abroad

Foreign spouses and foreign-citizen dependents apply for an ITIN by filing Form W-7 (Application for IRS Individual Taxpayer Identification Number) with their U.S. tax return.

The W-7 process has three paths:

1. With the tax return (most common)

You attach the W-7 to the U.S. tax return where you're claiming the foreign person (typically a joint return with a foreign spouse, or claiming a foreign dependent). You include:

• Completed Form W-7 for each applicant
• Original or certified-copy passport (or other ID documents from the IRS-approved list)
• The actual tax return that requires the ITIN

The whole package is mailed to the IRS ITIN Operations address (Austin, TX). Processing takes 7–11 weeks; longer for international applicants. You don't file the return electronically — paper-file with the ITIN application.

2. Through an IRS Certifying Acceptance Agent (CAA)

A CAA is an authorized professional who can verify your documents and submit the W-7 on your behalf, without sending your original passport to the IRS. There are CAAs in many countries.

This is the recommended path if you don't want to mail your original passport abroad and wait several months for its return.

3. At an IRS Taxpayer Assistance Center

In some countries with a U.S. tax presence (Frankfurt, London, Paris, Beijing — though the IRS has reduced international offices), you can apply in person and have your documents verified on the spot.

ITIN renewals

ITINs expire if not used on at least one federal tax return for three consecutive years. Once expired, you must reapply with a new W-7. Plan accordingly if you're a foreign spouse who's not consistently included on a U.S. tax return.

ITINs issued before 2013 had no specific expiration; many of those have since been administratively expired by the IRS.

The "electing to treat my non-U.S. spouse as a resident" issue

Many expat U.S. citizens face this choice: file Married Filing Jointly (treating the non-U.S. spouse as a U.S. resident for tax purposes — which requires the spouse to have a U.S. tax ID) or Married Filing Separately (with the brutally low $5 filing threshold).

If you elect MFJ:

• Your spouse needs an ITIN.
• Your spouse's worldwide income becomes part of your joint return.
• You get full MFJ tax brackets, standard deduction, and CTC mechanics.
• You can use FEIE and FTC against the joint income.

For families where the non-U.S. spouse has low to moderate foreign income, MFJ is usually better — the lower brackets and CTC outweigh the additional taxable income.

For families where the non-U.S. spouse has very high foreign income that would push the joint return into higher brackets, MFS may be cheaper, but the $5 threshold means careful planning to avoid losing FEIE on the U.S.-citizen side.

Common ITIN-vs-SSN mistakes

• Not registering U.S.-citizen kids for SSN. Every year of delay = lost CTC.
• Using an ITIN where an SSN is required. ITIN doesn't substitute for SSN for CTC, EITC, etc.
• Letting an ITIN expire. Three years without use means reapplication.
• Mailing the actual original passport with the W-7. Possible to do but slow and risky. Use a Certifying Acceptance Agent instead.
• Confusing ITIN and EIN. ITIN is for individuals; EIN is for business entities. If you've started a business abroad and need a U.S. tax ID for the business, you need an EIN (Form SS-4), not an ITIN.

Children with both U.S. and foreign citizenship

A child born to a U.S.-citizen parent abroad — and to a foreign-citizen parent — is typically a dual citizen under both countries' laws. For U.S. tax purposes, only U.S. citizenship matters: the child is a U.S. person, needs an SSN, files U.S. tax returns once income thresholds are met, qualifies for CTC for the parents.

Their other citizenship doesn't change any U.S. obligation. They are simultaneously taxed by the U.S. on worldwide income and (potentially) by the other country.

Next steps

• Who must file as a U.S. expat
• Child Tax Credit from abroad
• Marrying a non-U.S. citizen: tax implications
• Kids born abroad: citizenship and tax