A Social Security number (SSN) is a 9-digit number issued by the Social Security Administration (SSA), while an ITIN is a 9-digit tax-processing number issued by the IRS to people who need a taxpayer ID but aren't eligible for an SSN.

They look alike on purpose. Both are written NNN-NN-NNNN, and an ITIN always begins with the digit 9. But they're different numbers from different agencies, and they do different jobs. Mixing them up is a common source of rejected tax forms and confusing letters.

This page describes the rules as the agencies state them. Whether you're eligible for either number depends on your own situation, so confirm it with the IRS or SSA.

What an ITIN and an SSN are

The IRS calls both of these taxpayer identification numbers (TINs). An SSN is issued by the SSA, and, in the IRS's words, all other TINs are issued by the IRS. People use an SSN for much more than taxes. SSA lists filing taxes, starting a job, opening a bank account, applying for a loan, getting a passport, and claiming government benefits among the reasons you may need one.

An ITIN is narrower. The IRS says it's issued for federal tax purposes only, and it doesn't qualify you for Social Security benefits or the Earned Income Tax Credit, doesn't provide or change immigration status, doesn't authorize you to work legally in the US, and doesn't serve as identification outside the federal tax system.

The IRS also says you can't have both numbers. If you later become eligible for an SSN, you stop using the ITIN and tell the IRS, so your tax records are combined under the SSN. Otherwise you may not get credit for all wages paid and taxes withheld.

What it looks like

SSN ITIN
Issued by Social Security Administration IRS
Format 9 digits, NNN-NN-NNNN 9 digits, NNN-NN-NNNN, begins with 9
Who it's for People eligible for an SSN People with a federal tax purpose who aren't eligible for an SSN
Application form Form SS-5, plus evidence of identity, age, and US citizenship or lawful alien status Form W-7, plus documents proving identity and foreign/alien status
How it arrives Card by mail, 5 to 10 business days after approval (SSA) Notice CP565, about 7 weeks (9 to 11 in tax season or from overseas) (IRS)
Used for Taxes, work, banking, benefits, and more Federal tax filing and related tax purposes only
Work authorization Not covered on the pages cited here; ask SSA Does not authorize work (IRS)

Who doesn't need an ITIN, per the IRS: US citizens, green card holders, nonresident aliens with a US work visa (who qualify for an SSN), and anyone eligible for an SSN.

What to keep and for how long

  • Your SSN card or number. Keep the card, or a secure record of the number, in a safe place. SSA notes a physical card often isn't needed day to day, and a replacement is free.
  • Your ITIN notice (CP565). It's the proof of the number the IRS assigned you. The IRS says if you lose it, you contact the IRS.
  • A copy of your Form W-7 package. The IRS says the ITIN assignment date can affect eligibility for certain credits, so the date matters.
  • Tax records. The IRS says to keep records that support income, deductions, or credits until the period of limitations runs out, generally 3 years from filing, longer in some cases.

If you change your name, the IRS asks you to notify it in writing with documentation, such as a marriage certificate.

Both numbers are sensitive, so keep any scans somewhere locked rather than loose in your camera roll. For card handling, see whether to laminate a Social Security card, and for the wider document picture, immigration paperwork.

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