The IRS uses five different taxpayer identification number types, and which one you need depends on who you are and why you’re filing. Individuals use a Social Security Number (SSN) or, if they aren’t eligible for one, an Individual Taxpayer Identification Number (ITIN). Businesses and other entities use an Employer Identification Number (EIN). Adoptive parents in the middle of a pending domestic adoption may need an Adoption Taxpayer Identification Number (ATIN). Paid tax preparers need a Preparer Taxpayer Identification Number (PTIN). Every one of them is nine digits, and every return or tax document filed with the IRS needs one.
The Five Types and Who Uses Each
The SSN is the default identifier for U.S. citizens and authorized residents. If you’re eligible for one, that’s what goes on your personal return.
The ITIN is for individuals who have a federal tax filing obligation but aren’t eligible for an SSN, including certain nonresident aliens and their dependents.1Internal Revenue Service. About Form W-7, Application for IRS Individual Taxpayer Identification Number
The EIN is used by corporations, partnerships, trusts, estates, and other non-individual entities for payroll taxes and business returns. A sole proprietor with no employees can often use their SSN for business tax purposes, but once you hire employees, open a Keogh or Solo 401(k), file excise tax returns, or buy an existing business, federal law requires you to get an EIN.2eCFR. 26 CFR 301.6109-1 – Identifying Numbers
The ATIN is a temporary number for a child in a pending domestic adoption, used when the adoptive parents can’t yet obtain the child’s SSN.3Internal Revenue Service. Adoption Taxpayer Identification Number
The PTIN is required for anyone who prepares federal tax returns for compensation, and for enrolled agents regardless of whether they prepare returns.4Internal Revenue Service. PTIN Requirements for Tax Return Preparers
How to Tell Them Apart at a Glance
SSNs and ITINs share the same nine-digit format: XXX-XX-XXXX. Every ITIN starts with a 9, and the fourth and fifth digits fall inside specific ranges (50–65, 70–88, 90–92, or 94–99), so they never overlap with SSNs.5Internal Revenue Service. Individual Taxpayer Identification Number
EINs use a different layout: XX-XXXXXXX — two digits, a hyphen, then seven.6Internal Revenue Service. Understanding Your EIN Entering a number in the wrong format on a return causes processing delays.
How to Get an EIN
Businesses apply using Form SS-4. The form asks for the entity’s legal name, entity type (corporation, partnership, LLC, and so on), and the name and SSN or ITIN of a “responsible party” — the person who owns or controls the entity and manages its funds.7Internal Revenue Service. Responsible Parties and Nominees The responsible party must be an individual, not another entity, with the sole exception being government agencies.8Internal Revenue Service. Form SS-4 – Application for Employer Identification Number
The IRS online EIN assistant issues the number immediately. It runs Monday through Friday from 6:00 a.m. to 1:00 a.m. Eastern, Saturdays from 6:00 a.m. to 9:00 p.m., and Sundays from 6:00 p.m. to midnight. You’re limited to one EIN per responsible party per day, and the tool only works if your principal business location is in the United States or its territories.9Internal Revenue Service. Get an Employer Identification Number Businesses based outside the U.S. apply by phone, fax, or mail.
How to Get an ITIN
If you need to file a federal return but aren’t eligible for an SSN, apply on Form W-7. You have to establish both your identity and your foreign status. A valid passport does both on its own. Without a passport, you’ll need at least two documents from the IRS’s accepted list, and at least one must include a photograph.10Internal Revenue Service. Instructions for Form W-7 Other accepted documents include a national identification card, a birth certificate, a visa, and foreign or U.S. driver’s licenses.
You can mail Form W-7 to the IRS ITIN Operation center in Austin, Texas, along with your tax return and original or certified documents. The IRS returns your originals after processing. If mailing originals isn’t an option, visit a designated IRS Taxpayer Assistance Center for in-person verification, or work with a Certifying Acceptance Agent authorized by the IRS to authenticate documents and submit the application for you.11Internal Revenue Service. ITIN Acceptance Agent Program
Normal processing runs about seven weeks. During tax season (January 15 through April 30) or for applications sent from overseas, expect nine to eleven weeks.12Internal Revenue Service. How to Apply for an ITIN
ITINs Expire
If you don’t use your ITIN on a federal return for three consecutive years, it expires on December 31 after that third year of non-use. Filing a return with an expired ITIN can delay processing and cost you eligibility for certain tax credits, producing a smaller refund or triggering penalties and interest.13Internal Revenue Service. How to Renew an ITIN To renew, submit a new Form W-7 through any of the same channels. It doesn’t need to be attached to a tax return unless you’re filing at the same time.
How to Get an ATIN
You qualify for an ATIN only if the child was legally placed in your home by an authorized agency, you’ve made a reasonable effort to obtain the child’s existing SSN and couldn’t, and the Social Security Administration won’t issue a new one yet.3Internal Revenue Service. Adoption Taxpayer Identification Number Apply on Form W-7A with your placement documentation. The IRS recommends applying at least eight weeks before your return deadline, since processing takes four to eight weeks.
Once the adoption is final, get an SSN for the child and notify the IRS so it can deactivate the ATIN. If you don’t notify the IRS within two years, the ATIN deactivates automatically. A reminder notice goes out at eighteen months.3Internal Revenue Service. Adoption Taxpayer Identification Number
How to Get a PTIN
A valid PTIN is required before you touch a single return for compensation. For 2026, a new or renewed PTIN costs $18.75, and most first-time applicants complete the online process in about 15 minutes.4Internal Revenue Service. PTIN Requirements for Tax Return Preparers The paper alternative is Form W-12, which takes about six weeks. PTINs renew annually, so a valid 2026 PTIN is required before preparing any returns for the 2026 filing season.
What Happens if a TIN Is Wrong or Missing
For individuals, the immediate consequence is backup withholding. If you fail to give a payer (a bank, brokerage, or client) your correct TIN, or the IRS notifies the payer that the TIN you provided is wrong, the payer must withhold a flat 24% from your future payments of interest, dividends, and certain other income.14Internal Revenue Service. Backup Withholding That money credits against your tax liability, but it’s tied up until you file and reconcile.
Businesses face separate penalties for filing information returns (like W-2s and 1099s) with missing or incorrect TINs. The 2026 amounts scale with how quickly you correct the error:
- Corrected within 30 days: $60 per return
- Corrected after 30 days but by August 1: $130 per return
- Not corrected after August 1 or never filed: $340 per return
- Intentional disregard: $680 per return
These are the 2026 figures.15Internal Revenue Service. Information Return Penalties For a business issuing hundreds of 1099s, a batch of bad TINs adds up fast.