A tax identification number is a nine-digit code the IRS uses to track a person’s or entity’s tax records, and federal law requires one on every return, information filing, and many financial account applications. Which type you need depends on who you are: U.S. citizens and permanent residents use a Social Security Number, businesses use an Employer Identification Number, foreign filers without SSN eligibility use an Individual Taxpayer Identification Number, adoptive parents use an Adoption Taxpayer Identification Number for a child pending placement, and paid tax preparers use a Preparer Tax Identification Number. The authority sits in 26 U.S.C. § 6109, which lets the IRS demand an identifying number from anyone filing a return, statement, or other tax document.1Office of the Law Revision Counsel. 26 USC 6109 – Identifying Numbers
The Five Types and Who Uses Each
Social Security Number (SSN)
The SSN is the most common TIN. The Social Security Administration issues it to U.S. citizens and permanent residents, and to some noncitizens with work authorization. The number stays with you for life and tracks earnings, benefit eligibility, and tax filings.2Social Security Administration. Request a Social Security Number for the First Time
Employer Identification Number (EIN)
An EIN is the business counterpart to an SSN. The IRS assigns EINs to corporations, partnerships, LLCs, tax-exempt organizations, trusts, estates, and other entities that file returns or pay employment taxes.3Internal Revenue Service. Employer Identification Number You also need one to withhold taxes on payments to nonresident aliens or to operate a retirement plan. Sole proprietors sometimes get one just to keep their SSN off business paperwork.
Individual Taxpayer Identification Number (ITIN)
If you have a U.S. tax obligation but can’t get an SSN, you need an ITIN. It applies most often to nonresident aliens with U.S. income, foreign nationals filing a return, and dependents or spouses claimed on someone else’s return who don’t qualify for an SSN.4Internal Revenue Service. Individual Taxpayer Identification Number (ITIN)
An ITIN is only for federal tax processing. It does not authorize work in the U.S., qualify you for Social Security benefits, or make you eligible for the Earned Income Tax Credit.4Internal Revenue Service. Individual Taxpayer Identification Number (ITIN)
Adoption Taxpayer Identification Number (ATIN)
An ATIN is a temporary number for a child placed with prospective adoptive parents when the adoption isn’t final. The SSA often won’t issue an SSN for a child until the adoption is complete, and parents still need a number to claim the child as a dependent.5eCFR. 26 CFR 301.6109-3 – IRS Adoption Taxpayer Identification Numbers Once the adoption is final, you apply for an SSN for the child and stop using the ATIN. If the IRS isn’t notified of the new SSN within two years, the ATIN is automatically deactivated.6Internal Revenue Service. Adoption Taxpayer Identification Number
Preparer Tax Identification Number (PTIN)
Anyone who prepares or helps prepare federal tax returns for pay must have a PTIN, including signing preparers, non-signing preparers, and paid interns.7Internal Revenue Service. Frequently Asked Questions – Do I Need a PTIN The number goes in the “Paid Preparer” section of each return so the IRS can track who filed what. The fee for a new PTIN or annual renewal is $18.75.8Internal Revenue Service. PTIN Requirements for Tax Return Preparers
When You Actually Need One
Every federal tax return needs a valid TIN. A missing or wrong number can get the return rejected, delay a refund, or trigger penalties.
Banks and credit unions require a TIN to open an account, a requirement of federal know-your-customer and anti-money-laundering rules. Mortgage lenders, credit card issuers, and personal-loan lenders pull credit using your TIN to price the loan.
Employers use your SSN to report wages and withhold tax. Businesses use their EIN to file payroll returns, issue W-2s, and report dividends. If you pay a contractor more than $600 in a year, you need their TIN for the 1099.
When a payee fails to provide a correct TIN, the payer may have to withhold 24% of the payment as backup withholding and send it to the IRS. The money is credited toward the payee’s tax bill, but it ties up cash in the meantime.
How to Apply for Each Type
SSN
Apply on Form SS-5 with the Social Security Administration.9Social Security Administration. Social Security Forms You need at least two documents proving age, identity, and citizenship or immigration status. U.S. citizens can usually use a birth certificate and a government ID. Noncitizens submit immigration documents showing work authorization.10Social Security Administration. Application for Social Security Card Processing normally runs about two weeks after the SSA has all documents, and up to four weeks for noncitizens if immigration status needs verification with DHS.11Social Security Administration. Social Security Numbers and Immigrant Visas
EIN
The fastest route is the IRS online application, which issues the EIN immediately once you finish. The tool runs Monday through Friday from 6:00 a.m. to 1:00 a.m. Eastern, Saturday 6:00 a.m. to 9:00 p.m., and Sunday 6:00 p.m. to midnight. You’re limited to one EIN per responsible party per day, and the session times out after 15 minutes of inactivity with no way to save progress. If your principal place of business is outside the U.S., you can’t use the online tool; apply by phone, fax, or mail with Form SS-4.12Internal Revenue Service. Get an Employer Identification Number
ITIN
Use Form W-7.13Internal Revenue Service. About Form W-7, Application for IRS Individual Taxpayer Identification Number A passport is the only standalone document the IRS accepts because it proves both identity and foreign status. Without a passport, you need at least two documents from a list that includes foreign driver’s licenses, national identification cards, civil birth certificates, and U.S. visas.14Internal Revenue Service. Instructions for Form W-7
The IRS wants originals or certified copies from the issuing agency, which you may not see again for weeks. A Certifying Acceptance Agent can authenticate your documents and return them to you immediately.15Internal Revenue Service. ITIN Acceptance Agents Processing takes about seven weeks under normal conditions, and nine to eleven weeks during tax season (January 15 through April 30) or for applications from overseas.16Internal Revenue Service. How to Apply for an ITIN
ATIN
Prospective adoptive parents apply on Form W-7A. The child must have been placed in your household by an authorized placement agency, and the SSA must be unable to issue an SSN because the adoption isn’t final.6Internal Revenue Service. Adoption Taxpayer Identification Number5eCFR. 26 CFR 301.6109-3 – IRS Adoption Taxpayer Identification Numbers
PTIN
Apply or renew through the IRS online system, or by paper on Form W-12. The $18.75 fee is non-refundable and applies either way. A new PTIN must be issued, or an existing one renewed, before the start of each filing season.8Internal Revenue Service. PTIN Requirements for Tax Return Preparers
ITINs Expire — Watch the Three-Year Gap
An ITIN isn’t permanent. If yours isn’t included on a federal return for three consecutive years, it expires on December 31 of that third year.17Internal Revenue Service. How to Renew an ITIN Anyone who had a gap in filing may find their old number is already dead when they need to file again.
Renewal uses the same Form W-7, with the “Renew an existing ITIN” box checked and your old ITIN entered if you know it. You still list your reason for submitting the form. Spouses and dependents renewing for an allowable tax benefit must appear on an attached federal return with the relevant schedule or form. Include supporting documentation like a marriage certificate or court order if your legal name changed since the ITIN was first issued.17Internal Revenue Service. How to Renew an ITIN
Penalties for a Missing or Incorrect TIN
Under IRC § 6721, filing an information return (a 1099 or W-2, for example) with a wrong TIN or no TIN carries a 2026 penalty of $60 per return if corrected within 30 days, $130 if corrected by August 1, and $340 per return if never corrected or filed after August 1.18Internal Revenue Service. Information Return Penalties Intentional disregard raises the figure to $680 per return. For a business filing hundreds of information returns, the totals climb quickly.
For individuals, the more common consequence is a delayed refund. The IRS matching system checks the TIN on your return against employer and bank records, and a mismatch flags the return for manual review, pushing the refund back by weeks or months.
Protecting Your Number With an IP PIN
Tax-related identity theft happens when someone files a fraudulent return using your SSN or ITIN. The IRS Identity Protection PIN is a six-digit code that blocks any filing under your number without it.19Internal Revenue Service. Get an Identity Protection PIN
Anyone with an SSN or ITIN can enroll. The quickest way is through your IRS online account, where the PIN appears in your profile. If you can’t create an online account and your adjusted gross income is below $84,000 ($168,000 for married filing jointly), file Form 15227 and verify your identity by phone; the PIN arrives by mail in four to six weeks. As a last option, visit a local Taxpayer Assistance Center in person with photo ID and receive the PIN by mail in about three weeks.19Internal Revenue Service. Get an Identity Protection PIN
The IP PIN changes every year. Online enrollees retrieve the new one from their account each January. Phone and in-person enrollees receive a new CP01A notice by mail annually. You need the current year’s PIN on any federal return filed that year, prior-year returns included.