A Taxpayer Identification Number, or TIN, is a nine-digit number the IRS uses to track your earnings, process your tax returns, and identify you on other financial records. Every person and business that files a federal tax return, earns income, or opens a financial account in the United States needs one. The type you need depends on whether you’re a U.S. citizen, a foreign national filing taxes here, or an entity like a business, trust, or estate.
The Five Types of TIN
The IRS recognizes five identifying numbers under the TIN umbrella. Three cover almost everyone; two apply to narrower situations.
Social Security Number
The Social Security Administration issues SSNs to U.S. citizens, permanent residents, and certain non-citizens authorized to work in the country. An SSN tracks your lifetime earnings for future Social Security benefits and doubles as your primary tax identification number. Most Americans receive one in infancy, but anyone who becomes eligible later can apply.
Individual Taxpayer Identification Number
An ITIN is a nine-digit number beginning with “9” that the IRS issues to people who need to file a U.S. tax return but cannot get an SSN. This includes certain nonresident aliens, resident aliens, and their spouses or dependents claimed on a return. An ITIN exists solely 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 change your immigration status.1Internal Revenue Service. Individual Taxpayer Identification Number (ITIN) It is a tax-filing tool, nothing more.
Employer Identification Number
An EIN is a nine-digit number, formatted XX-XXXXXXX, that the IRS assigns to businesses, estates, trusts, and other entities. It functions as a Social Security Number for the entity, identifying it 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
Adoption Taxpayer Identification Number
An ATIN is a temporary number the IRS assigns to a child in the adoption process when the adoptive parents can’t yet obtain the child’s SSN. Adoptive parents apply using Form W-7A. The ATIN automatically expires two years after issuance, by which point the child should have an SSN.3Legal Information Institute. Adoption Taxpayer Identification Number (ATIN)
Preparer Taxpayer Identification Number
A PTIN is required for anyone who prepares federal tax returns for compensation. Attorneys and CPAs only need a PTIN if they are 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 you to include a TIN on returns, statements, and other tax-related documents.5Office of the Law Revision Counsel. 26 USC 6109 – Identifying Numbers The moments you’ll be asked to produce yours reach well beyond tax season.
For individuals, an SSN or ITIN is needed to file a federal return. An SSN is typically required to start a new job, apply for Social Security or Medicare benefits, 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 to issue a driver’s license.
Businesses that hire employees need an EIN to report payroll taxes. Corporations and partnerships need one whether or not they have employees. An EIN is also required to open a business bank account, file business returns, and apply for licenses and permits. When a revocable trust becomes irrevocable after the grantor’s death, the successor trustee must get a new EIN because the trust can no longer use the deceased grantor’s SSN.2Internal Revenue Service. Get an Employer Identification Number
Banks collect a TIN before opening any new account under the Customer Identification Program, part of the Bank Secrecy Act. Whether it’s a personal checking account tied to your SSN or a trust account tied to an EIN, the bank has to verify your identity using the number. There’s no way around it.
How to Get a Social Security Number
U.S. citizens, permanent residents, and non-citizens authorized to work in the U.S. can apply. Complete Form SS-5 and provide original documents proving your 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 won’t work.
You can submit by mail or in person at a local SSA office. If you’re 12 or older and have never had an SSN, you 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.
How to Get an ITIN
If you need to file a U.S. tax return but aren’t eligible for an SSN, apply for an ITIN using IRS Form W-7.8Internal Revenue Service. Form W-7 – Application for IRS Individual Taxpayer Identification Number Attach documentation proving your foreign status and identity, plus a completed federal tax return unless you qualify for an exception. You can submit by mail to the IRS, through an IRS-authorized Acceptance Agent, or in person at an IRS Taxpayer Assistance Center.9Internal Revenue Service. Instructions for Form W-7
The IRS requires original documents or certified copies from the issuing agency. Sending a passport by mail makes people understandably nervous, which is why many applicants work through an Acceptance Agent (often a CPA or enrolled agent authorized to verify documents on the IRS’s behalf) or visit a Taxpayer Assistance Center in person.
ITINs also expire. Any ITIN not used on a federal tax return for three consecutive years expires on December 31 of that third year. ITINs assigned before 2013 that were never renewed have already expired.10Internal Revenue Service. Topic No. 857 – Individual Taxpayer Identification Number (ITIN) To renew, file a new Form W-7 with the “Renew an existing ITIN” box checked. Filing with an expired ITIN can delay your refund and disqualify you from certain credits.11Internal 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 explicitly warns against third-party websites that charge for the service.2Internal Revenue Service. Get an Employer Identification Number The fastest route is the IRS online application, which assigns your EIN immediately. You’ll need the responsible party’s SSN or ITIN and 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 entity and not a nominee with only 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.12Internal Revenue Service. Responsible Parties and Nominees
If your entity’s principal place of business is outside the United States, or if you don’t have an SSN or ITIN for the responsible party, you cannot use the online tool. Apply by phone, fax, or mail using Form SS-4 instead. Form SS-4 works for any entity type: employers, sole proprietors, corporations, partnerships, estates, and trusts.13Internal Revenue Service. About Form SS-4 – Application for Employer Identification Number
What Goes Wrong Without a Correct TIN
Skipping your TIN or providing a wrong one creates real financial consequences, not just paperwork delays.
Backup Withholding
If you fail to 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 that money to the IRS. This is called backup withholding, and it continues until you furnish the correct number.14Office of the Law Revision Counsel. 26 USC 3406 – Backup Withholding You can recover the withheld amount by filing a return and claiming it as a credit, but your money is tied up until then.
Penalties on Information Returns
Businesses that file 1099s and other information returns with a missing or incorrect TIN face per-return penalties, with higher amounts for intentional disregard.15Internal Revenue Service. IRS Internal Revenue Manual 20.1.7 The penalty falls on the filer, not the individual whose number is wrong, which is why payers push hard for a correct TIN before year-end.
Rejected or Delayed Returns
An e-filed return with a missing, expired, or mismatched TIN is rejected outright. A paper return with the same problem is set aside for manual review, which can delay a refund by months. If you claim dependents, each dependent’s TIN must match IRS records too. One wrong digit on a child’s SSN can hold up the whole return.
Protecting Your TIN
Your TIN is the key to your tax identity, and stolen numbers are the raw material for most tax-related fraud. Someone with your SSN can file a bogus return in your name and collect your refund before you file. A few habits cut that risk.
Don’t carry your Social Security card in your wallet. Shred documents showing your full TIN before throwing them away. Be skeptical of anyone requesting your TIN by phone or email; the IRS initiates most contact by mail. Review your credit reports regularly and act quickly on accounts you don’t recognize.
The IRS also offers a free Identity Protection PIN, a six-digit number known only to you and the IRS that must appear on your return before it will be accepted. Without the correct IP PIN, a thief who has your SSN still can’t file in your name. Anyone with an SSN or ITIN can enroll through their IRS online account, by submitting Form 15227, or in person at a Taxpayer Assistance Center.16Internal Revenue Service. Get an Identity Protection PIN A new IP PIN is generated 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 suspected SSN theft, and the three major credit bureaus to place fraud alerts. The earlier you act, the less damage there is to undo.