What an ITIN is, who needs one, and how to apply

If you work in the United States, or have to file a return here, but don't qualify for a Social Security number, the IRS issues a different number for that purpose: an ITIN. It exists only for the federal tax system, and understanding that before you start matters.

What it actually is

ITIN stands for Individual Taxpayer Identification Number. It's a nine-digit number the IRS issues so that someone can meet their tax obligations when they don't have — and can't get — a Social Security number.

Who needs one

• You have to file a federal return and don't qualify for a Social Security number.
• Your spouse will be on a joint return and has no number.
• You're claiming a dependent who has no number of their own.
• You're a foreign student, professor or researcher with a filing requirement.

Which documents the IRS accepts

The Form W-7 instructions list thirteen acceptable documents. Of all of them, a passport is the only one the IRS calls a stand-alone document: present it and nothing else is needed to prove identity and foreign status at the same time. Every other route means combining two documents.

Why it matters who files it

If you file Form W-7 on your own, the IRS wants your ORIGINAL passport mailed in, or a certified copy issued by the agency that produced it — in practice, a consular appointment. Either way you're without your document for weeks.

A Certifying Acceptance Agent (CAA) is an office the IRS authorizes to verify those documents. The agent reviews the original in front of you, keeps a copy certified by the agent, issues a Certificate of Accuracy, and hands your passport straight back.

Form W-7 rarely travels alone

The general rule is that Form W-7 is filed together with the tax return the number is needed for. The instructions carve out five specific exceptions — withholding on passive income, scholarships, mortgage interest, dispositions of real property, and a Treasury Decision 9363 case — but outside those, applying for an ITIN on its own isn't the path.

ITINs expire

If an ITIN isn't used on a federal return for three consecutive tax years, it expires on December 31 of that third year. To use it on a return again you renew it, with Form W-7 once more, checking the renewal box.

Filing with an expired ITIN doesn't get the return thrown out automatically, but it can delay your refund and leave you out of certain credits until the renewal goes through.