A Taxpayer Identification Number, or TIN, is a nine-digit number the IRS uses to identify you, your family members, or your business on tax returns and other financial records. It isn’t a single number issued by one office. It’s a category that covers several different numbers, and which one you need depends on who you are: a U.S. citizen or authorized worker, a foreign filer, a business, or someone in a narrower situation like adoption or paid tax preparation.
The Main Types of TIN
Three TINs cover almost everyone.
Social Security Number (SSN)
The Social Security Administration issues SSNs to U.S. citizens, permanent residents, and non-citizens authorized to work in the United States. Your SSN tracks your lifetime earnings for Social Security purposes and serves as your primary tax ID. Most people get one in infancy; anyone who becomes eligible later can apply.
Individual Taxpayer Identification Number (ITIN)
An ITIN is a nine-digit number beginning with “9” that the IRS issues to people who must file a U.S. tax return but can’t get an SSN. That includes certain nonresident aliens, resident aliens, and their spouses or dependents. An ITIN exists only for federal tax purposes. It does not authorize you to work in the United States, does not qualify you for Social Security benefits or the Earned Income Tax Credit, and does not affect your immigration status.1Internal Revenue Service. Individual Taxpayer Identification Number (ITIN)
Employer Identification Number (EIN)
An EIN is a nine-digit number formatted XX-XXXXXXX that the IRS assigns to businesses, estates, trusts, and other entities. It functions the way an SSN does for a person: the IRS uses it to identify the entity on tax filings, payroll reports, and other documents. You generally need an EIN if you plan to hire employees, operate as a corporation or partnership, pay excise taxes, administer certain trusts or retirement plans, or handle a deceased person’s estate.2Internal Revenue Service. Get an Employer Identification Number
Two Narrower TINs
An Adoption Taxpayer Identification Number (ATIN) is a temporary number the IRS assigns to a child in the adoption process when adoptive parents can’t obtain the child’s SSN. It’s requested on Form W-7A and expires automatically two years after issuance, by which point the child should have an SSN.3Legal Information Institute. Adoption Taxpayer Identification Number (ATIN) A Preparer Taxpayer Identification Number (PTIN) is required for anyone who prepares federal tax returns for compensation. Attorneys and CPAs need one only if they’re preparing substantially all of a return for pay.4Internal Revenue Service. Frequently Asked Questions – Do I Need a PTIN?
When You Actually Need a TIN
Federal law requires a TIN on returns, statements, and other tax-related documents.5Office of the Law Revision Counsel. 26 USC 6109 – Identifying Numbers But you’ll be asked for one in plenty of situations outside of tax filing.
As an individual, you need an SSN or ITIN to file a federal income tax return. An SSN is typically required to start a new job, apply for Social Security or Medicare, open bank and investment accounts, and apply for federal student aid through FAFSA.6Federal Student Aid. 2025-2026 Federal Student Aid Handbook – Chapter 4 Social Security Number Most states also require an SSN for a driver’s license.
A business needs an EIN to report payroll taxes if it has employees. Corporations and partnerships need one regardless of whether they have employees. You’ll also need an EIN to open a business bank account, file business tax returns, or apply for business licenses. When a revocable trust becomes irrevocable after the grantor’s death, the successor trustee must get a new EIN for the trust because it can no longer use the grantor’s SSN.2Internal Revenue Service. Get an Employer Identification Number
Banks are required to collect a TIN before opening new accounts under federal anti-money-laundering rules. Whether the account is personal (SSN) or entity (EIN), the bank verifies your identity using your TIN, and there’s no way around this step.
How to Get a Social Security Number
U.S. citizens, permanent residents, and non-citizens authorized to work here can apply for an SSN using Form SS-5, along with original documents proving age, identity, and citizenship or immigration status.7Social Security Administration. Application for a Social Security Card The SSA accepts originals or copies certified by the issuing agency. Notarized photocopies aren’t accepted.
You can apply by mail or in person at a local SSA office. Anyone 12 or older applying for the first time must apply in person.7Social Security Administration. Application for a Social Security Card The SSA returns your original documents and mails your card separately, usually within a few weeks.
If you change your legal name through marriage, divorce, or a court order, update your SSA record so it matches the name on your tax returns. There’s no hard deadline, but updating within two years of the change is easier because the SSA will accept your marriage certificate or court order as primary identification. After that, ID requirements tighten.
How to Get an ITIN
If you must file a U.S. tax return but aren’t eligible for an SSN, you apply for an ITIN using Form W-7, attaching documents that prove foreign status and identity along with a completed federal tax return (unless you qualify for an exception). Form W-7 can be mailed to the IRS, filed through an IRS-authorized Acceptance Agent, or submitted in person at an IRS Taxpayer Assistance Center.8Internal Revenue Service. Instructions for Form W-7
The IRS requires original documents or certified copies from the issuing agency. Because that often means sending a passport, many applicants use an Acceptance Agent (typically a CPA or enrolled agent authorized to verify documents on the IRS’s behalf) or visit a Taxpayer Assistance Center in person.
ITINs don’t last forever. An ITIN that isn’t used on a federal return for three consecutive years expires on December 31 of the third year. To renew, file a new Form W-7 with the “Renew an existing ITIN” box checked.9Internal Revenue Service. How to Renew an ITIN If you’ve since obtained an SSN, don’t renew — notify the IRS so it can combine your records under the SSN.
How to Get an EIN
Applying for an EIN is free, and the IRS warns against third-party sites that charge for the service.2Internal Revenue Service. Get an Employer Identification Number The fastest route is the IRS online application, which issues the EIN immediately. You’ll need the responsible party’s SSN or ITIN plus the entity’s name, address, and type.
The responsible party must be an individual who owns or controls the entity and manages its funds, not another business and not a nominee with limited formation authority. For a corporation, that’s the principal officer; for a partnership, a general partner; for an estate, the executor or personal representative.10Internal Revenue Service. Responsible Parties and Nominees
If the entity’s principal place of business is outside the United States, or if the responsible party has no SSN or ITIN, the online tool won’t work. Apply by phone, fax, or mail using Form SS-4 instead.11Internal Revenue Service. About Form SS-4 – Application for Employer Identification Number
What Happens When a TIN Is Missing or Wrong
Skipping a TIN or providing an incorrect one causes real problems, not just paperwork delays.
If you don’t give a correct TIN to a bank, brokerage, or other payer, federal law requires the payer to withhold 24% of your reportable payments (interest, dividends, and certain other income) and send it to the IRS. This backup withholding continues until you furnish the correct TIN.12Office of the Law Revision Counsel. 26 USC 3406 – Backup Withholding You can recover the money later by claiming it as a credit on your return, but it’s tied up in the meantime.
Businesses that file information returns (like 1099s) with a missing or incorrect TIN face per-return penalties. For 2026, the penalty ranges from $60 to $340 per return depending on how quickly it’s corrected, with an annual cap of $1,366,000 for small businesses (gross receipts of $5 million or less) and $4,098,500 for larger businesses. Intentional disregard carries $680 per return with no annual cap.13Internal Revenue Service. IRS Internal Revenue Manual 20.1.7 The penalty hits the filer, but payers will chase you hard for a correct number to avoid it.
An e-filed return with a missing, expired, or mismatched TIN is rejected outright. A paper return with the same problem gets pulled for manual review, which can delay your refund by months. Dependent TINs must match IRS records too. One wrong digit on a child’s SSN can hold up the entire return.
Protecting Your TIN From Identity Theft
A stolen SSN is the raw material for most tax-related fraud. Someone with your number can file a false return in your name and claim your refund, leaving you to untangle it with the IRS. A few habits reduce the risk: don’t carry your Social Security card in your wallet, shred documents that show your full TIN, and be skeptical of anyone requesting your TIN by phone or email. The IRS initiates most contact by mail.
The IRS also offers a free Identity Protection PIN (IP PIN), a six-digit number known only to you and the IRS that must appear on your tax return before it’s accepted. Without the correct IP PIN, a fraudster who has your SSN still can’t file in your name. Anyone with an SSN or ITIN can enroll, fastest through an IRS online account, or by submitting Form 15227 or visiting a Taxpayer Assistance Center.14Internal Revenue Service. Get an Identity Protection PIN A new IP PIN is issued each year and must be used on every federal return you file during that year, including prior-year returns.
If you think your TIN has already been compromised, contact the IRS, the SSA (for SSN theft), and the three major credit bureaus to place fraud alerts. The sooner you move, the easier the damage is to contain.