Your tax identification number is the nine-digit code the IRS uses to track your tax account

A tax identification number (TIN) is a nine-digit identifier the Internal Revenue Service assigns to you for tax purposes. The most common type is a Social Security Number (SSN), which you likely already have. If you don't have an SSN or are not may be able to access for one, the IRS issues an Individual Taxpayer Identification Number (ITIN) instead. Both serve the same function: they let the IRS match your income, deductions, and tax payments to your account.

You need a TIN to file a tax return, open a bank account, get a job, or claim dependents. Employers, banks, and investment firms all ask for it. The number itself doesn't reveal your identity — it's just the filing key the IRS uses to organize your records.

Key Takeaways

  • A Social Security Number is your tax identification number if you have one; an ITIN serves the same purpose if you don't have an SSN.
  • You can find your SSN on your Social Security card, tax returns, W-2 forms, or by contacting the Social Security Administration.
  • If you need an ITIN because you're not may be able to access for an SSN, you must file Form W-7 with the IRS and provide proof of identity and residency.
  • The IRS uses your TIN to match income reported by employers and financial institutions to your tax account.

Social Security Number as your primary tax ID

If you are a U.S. citizen or permanent resident, your Social Security Number is your tax identification number. You received it when you applied for Social Security benefits, usually as a child or when you first worked. Your SSN appears on your Social Security card, which the Social Security Administration mailed to you.

You can locate your SSN on several documents: your Social Security card itself, any tax return you've filed, a W-2 form from an employer, a 1099 form from a bank or investment account, or a mortgage statement. If you've lost track of it, you can contact the Social Security Administration directly by phone at 1-800-772-1213 or visit ssa.gov and use their online account lookup tool.

Individual Taxpayer Identification Number if you don't have an SSN

If you are not may be able to access for a Social Security Number — for example, if you are a nonresident alien, a dependent of a U.S. citizen, or a foreign national with a U.S. tax filing requirement — the IRS issues an Individual Taxpayer Identification Number (ITIN). An ITIN is also nine digits and works identically to an SSN for tax purposes, but it does not confer work authorization or Social Security benefits.

To obtain an ITIN, you must file Form W-7 (process for IRS Individual Taxpayer Identification Number) with the IRS. You'll need to provide proof of identity (such as a passport or national ID) and proof of residency (such as a utility bill, lease, or bank statement). You can mail the form and documents to the IRS, or in some cases visit an IRS office or an authorized acceptance agent in person. Processing typically takes four to six weeks by mail.

Why employers and financial institutions ask for your TIN

When you start a job, open a bank account, or invest money, you'll be asked to provide your tax identification number. Employers use it to file your W-2 form at year-end. Banks use it to report interest income on a 1099-INT. Investment firms use it to report dividends, capital gains, and brokerage activity. These reports go directly to the IRS and are matched to your account using your TIN.

If you provide the wrong number or refuse to provide one, the IRS may assess penalties, and your employer or financial institution may withhold taxes at a higher rate. Providing your correct TIN ensures that income reported to the IRS matches your tax return and prevents delays in processing refunds or notices.

Protecting your tax identification number

Your TIN is sensitive information. Someone with your SSN or ITIN can file a fraudulent tax return in your name, claim false refunds, or use it to open accounts. Treat it like you would a password: don't share it unless you know who is asking and why.

Legitimate employers, banks, and government agencies have a lawful reason to ask for your TIN. The IRS itself will never initiate contact by email, text, or social media to ask for your number. If you receive an unsolicited request, verify the sender's identity by calling the organization directly using a phone number from their official website or statement.

What to do if your TIN has been compromised

If you believe your SSN or ITIN has been stolen or misused, contact the Social Security Administration at 1-800-772-1213 if you have an SSN, or the IRS directly at 1-800-829-1040 if you have an ITIN. You can also file a report with the Federal Trade Commission at identitytheft.gov, which creates an official record and may help you dispute fraudulent accounts or tax returns.

If you suspect someone has filed a tax return using your number, file Form 14039 (Identity Theft Affidavit) with the IRS. Include a copy of any fraudulent return you've received and any supporting documentation. The IRS will investigate and contact you with next steps. Response times vary, but the IRS prioritizes identity theft cases.

Frequently Asked Questions

Can I have more than one tax identification number?

No. You should have only one TIN — either an SSN or an ITIN, not both. If you somehow obtained both, contact the Social Security Administration or IRS to have one cancelled. Having multiple numbers can create confusion in your tax records and delay processing.

Do I need a TIN if I don't work or file taxes?

If you have no income and no tax filing requirement, you may not need a TIN. However, you'll need one to open a bank account, get a job, or claim dependents on someone else's return. Most people obtain one early in life for these practical reasons, even if they don't when ready file taxes.

What's the difference between a TIN and an EIN?

A TIN is for individuals; an Employer Identification Number (EIN) is for businesses, partnerships, trusts, and nonprofits. If you are self-employed as a sole proprietor, you typically use your SSN or ITIN on your tax return, though you can obtain an EIN if you hire employees or form a business entity.

How long does it take to get an ITIN?

By mail, processing takes four to six weeks from the date the IRS receives your Form W-7 and supporting documents. In-person appointments at IRS offices or authorized acceptance agents may be faster in some locations. Check irs.gov for local office hours and appointment availability.

Can I look up someone else's tax identification number?

No. Your TIN is private information. The IRS does not release TINs to the public. If you need to verify someone's number for a legitimate business reason — such as reporting income to them — ask them directly or contact your accountant or attorney for guidance on proper procedures.