An ITIN is the IRS's answer to a real problem: people who have U.S. tax obligations but cannot get a Social Security Number. Non-resident aliens, foreign founders, foreign spouses of U.S. taxpayers, dependents claimed on U.S. returns — all of them need a tax identification number that is not an SSN. The ITIN is that number. This guide covers who qualifies, what documents the IRS accepts, where applications get stuck, and how the process actually runs in 2026.
What an ITIN Is
The Individual Taxpayer Identification Number is a nine-digit number issued by the IRS to individuals who must report taxes to the United States but are not eligible for an SSN. It always begins with the digit 9.
The ITIN is for tax administration only. It does not authorize you to work in the United States. It does not entitle you to Social Security benefits. It does not affect immigration status. It is purely a way for the IRS to track filings and process refunds for people who would otherwise fall outside the SSN system.
Who Needs an ITIN
You need an ITIN if you fall into any of these categories:
- Non-resident alien who must file a U.S. tax return — for U.S.-source income, rental income, royalty income, or investment gains
- U.S. resident alien (based on days present in the U.S.) filing a return who does not yet have an SSN
- Dependent or spouse of a U.S. citizen or resident alien being claimed on a joint return
- Dependent or spouse of a non-resident alien holding a visa
- Non-resident claiming a tax treaty benefit that requires a U.S. taxpayer ID on Form W-8BEN
- Foreign individual receiving distributions from a U.S. LLC taxed as a partnership
You do not need an ITIN if:
- You are eligible for an SSN (apply for an SSN, not an ITIN)
- You have no U.S. tax filing obligation (and have not been asked by a withholding agent for one)
- You only own a single-member foreign-owned LLC with no U.S. trade or business and no U.S.-source income — the LLC files Form 5472 with its EIN, but you personally may not need an ITIN
If you are unsure which category you are in, the deciding question is usually "do I have to file a U.S. tax return this year?" If yes, you need an ITIN. If no, hold off.
The Documents the IRS Accepts
The IRS publishes a specific list of acceptable identification documents. The only document that proves both identity and foreign status on its own is a valid passport. Everything else requires a combination of two documents.
The full accepted document list:
- Passport (standalone)
- National identification card with photograph
- U.S. driver's license
- Civil birth certificate (for dependents under 18)
- Foreign driver's license
- U.S. state identification card
- Foreign voter's registration card
- U.S. military identification card
- Foreign military identification card
- Visa
- USCIS photo identification
- Medical records (dependents only, under 6)
- School records (dependents only, under 14, or under 18 if a student)
For the vast majority of ITIN applications, the simple rule is: use a passport. It satisfies both requirements with one document and avoids the combinations that introduce risk.
Form W-7
Form W-7 is the ITIN application. It is two pages and asks for:
- Name as it appears on your passport
- Mailing address
- Birth information
- Country of citizenship
- Foreign tax identification number
- U.S. visa information, if applicable
- Reason for applying (this is critical — see below)
The "reason for applying" boxes on Form W-7 are not interchangeable. The IRS treats each as a different application category with different supporting requirements:
- (a) Non-resident alien required to obtain ITIN to claim tax treaty benefit
- (b) Non-resident alien filing a U.S. federal tax return
- (c) U.S. resident alien (based on substantial presence test) filing a U.S. tax return
- (d) Dependent of a U.S. citizen/resident alien
- (e) Spouse of a U.S. citizen/resident alien
- (f) Non-resident alien student, professor, or researcher filing a U.S. return or claiming an exception
- (g) Dependent/spouse of a non-resident alien holding a U.S. visa
- (h) Other
Most non-resident founders selecting an ITIN check (a), (b), or (h). Picking the wrong box is one of the more common reasons for application delay.
The Three Submission Paths
Mail directly to the IRS. Submit Form W-7, a U.S. federal tax return, and the original identification documents to the IRS ITIN Operation in Austin, Texas. The IRS holds your passport for 8 to 14 weeks while processing, then returns it. Risks: international mail is not insured, and you do not have your passport during that window.
In person at an IRS Taxpayer Assistance Center (TAC). Limited TACs accept ITIN applications. You bring the same documents. The TAC verifies your originals, returns them on the spot, and forwards the application to the IRS for processing. Practical only if you are in the U.S. and near a participating TAC.
Through a Certified Acceptance Agent. A CAA is authorized by the IRS to verify your original documents on the IRS's behalf and submit a certified copy with your W-7. You keep your originals. Processing through CAA channels is faster — most applications complete in 5 to 10 business days.
For non-residents, the CAA route is the only realistic option. Mailing an original passport to a U.S. processing center from abroad creates an unacceptable risk for what is solved with a 15-minute video verification call.
What Happens After You Apply
The IRS sends one of three outcomes:
- Assignment letter (CP-565). Your ITIN has been issued. The letter contains the number. Keep this letter — banks, employers, and the IRS itself may request a copy later.
- Rejection letter (CP-566 / CP-567). The application was rejected. The letter explains why and what to correct.
- Request for additional information. The IRS needs more documentation before deciding. Respond by the deadline in the letter.
Once issued, the ITIN is yours. It does not change. You use the same number across tax years.
Where Applications Fail
In our experience filing ITIN applications, the patterns are consistent:
- Name mismatch between Form W-7 and the passport. Spaces, hyphens, middle names, and name order have to match exactly.
- Missing tax return when one was required. Some W-7 reasons can be filed without a return; most cannot.
- Wrong reason box checked. Each box has different supporting requirements.
- Expired or near-expired passport. A passport with less than six months of validity is a frequent rejection cause.
- Names of dependents that don't match the tax return. Especially common where dependents have different surnames or family-naming conventions than U.S. forms expect.
Renewals
ITINs expire if not used on a U.S. tax return for three consecutive years. The renewal process uses the same Form W-7, with the "Renew an existing ITIN" box checked. Renewals are typically faster than initial applications because the IRS already has your identity on file.
If your ITIN has expired, renew before filing your next return — not at the same time. Filing both together stacks the timelines and delays any refund by 6 to 11 weeks.
How to Decide What to Do Next
If your situation is:
- Non-resident with U.S.-source income that requires a return → apply for an ITIN now, before tax season
- Foreign founder forming a U.S. LLC → form the LLC first, apply for the EIN, then decide whether you personally need an ITIN based on your filing obligations
- Spouse or dependent on a U.S. return → apply with the primary filer's return
- Treaty claim on Form W-8BEN → apply for the ITIN through the withholding agent's documentation requirements
The application itself is not the hard part. The hard parts are picking the correct reason box, matching documentation exactly to passport, and timing the W-7 against tax-season deadlines. Get those three right and the IRS does the rest.
