Types of Taxpayer ID Numbers: SSN, EIN, ITIN, ATIN, PTIN

The IRS recognizes five types of taxpayer identification numbers, and which one you need depends entirely on who you are and why you’re filing. The Social Security Number (SSN) covers most individual U.S. citizens and authorized workers. The Employer Identification Number (EIN) identifies businesses, trusts, and estates. The Individual Taxpayer Identification Number (ITIN) is for people with U.S. tax obligations who cannot get an SSN. The Adoption Taxpayer Identification Number (ATIN) is a temporary number for a child in a pending domestic adoption. The Preparer Taxpayer Identification Number (PTIN) is required of anyone paid to prepare tax returns. Federal law requires every return filer to include one of these nine-digit numbers, and each traces income, withholding, and compliance for a different kind of taxpayer.¹

Social Security Number

The SSN is the most common taxpayer ID. U.S. citizens and residents authorized to work in the United States apply through the Social Security Administration using Form SS-5. You show original documents proving age (typically a birth certificate), identity (an unexpired U.S. passport or state-issued ID), and citizenship or immigration status.² Permanent residents satisfy the immigration requirement with Form I-551, the green card. Photocopies and notarized copies are not accepted.

You can apply in person at a local Social Security office or by mailing Form SS-5 with your original documents. Adults who already have a number can often request a replacement card online through the SSA’s secure portal.³ When you mail originals, SSA returns them after verification, and the card typically arrives within 7 to 14 business days.² The number stays with you for life and serves as your primary link to individual income tax filings.

In limited cases, a person not authorized to work can receive a restricted SSN card marked “NOT VALID FOR EMPLOYMENT,” but only when a federal, state, or local law requires an SSN to receive a benefit the person already qualifies for.⁴

Employer Identification Number

Businesses, trusts, estates, and other entities use an EIN for federal tax reporting, hiring employees, and opening bank accounts. You apply on Form SS-4, listing the entity’s legal name, structure, principal activity, and a responsible party who has ultimate control over the organization.⁵ The fastest method is the IRS online application, which issues the EIN immediately on completion. The online tool is available 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.⁶

You can also submit Form SS-4 by fax or mail. Fax applications take about four business days; mailed applications can take four weeks. Once issued, an EIN stays with the entity for its entire legal existence, regardless of changes in name, address, or ownership.

When You Need a New EIN

Changing your business name or address does not require a new EIN, but changing your legal structure usually does. Sole proprietors need a new number if they incorporate, form a partnership, or declare bankruptcy. Corporations need one after receiving a new charter from the secretary of state, converting to a partnership or sole proprietorship, or merging to create a new corporation; electing S corporation status, reorganizing to change only identity or location, or surviving a merger does not require one. Partnerships need a new EIN when they incorporate, when one partner takes over as a sole proprietor, or when they dissolve and start a new partnership. LLCs need a new one if they terminate and form a new entity, or if a single-member LLC begins owing employment or excise taxes.⁷

Applying From Outside the United States

Foreign applicants with no legal residence, business address, or agency in the United States cannot use the online EIN tool. They can call the IRS at 267-941-1099 (not toll-free) Monday through Friday, 6:00 a.m. to 11:00 p.m. Eastern, to apply by phone.⁵ The caller must be authorized to answer questions about the entity and may be asked to fax or mail the signed Form SS-4 within 24 hours. If the responsible party has no SSN or ITIN, enter “foreign” or “N/A” on line 7b. Foreign applicants can also fax to 304-707-9471 or mail to the IRS EIN International Operation in Cincinnati, OH 45999.

Individual Taxpayer Identification Number

If you have a U.S. tax filing obligation but are not eligible for a Social Security Number, you need an ITIN. This applies primarily to nonresident aliens, their spouses and dependents, and resident aliens who lack work authorization.⁸ You apply using Form W-7 and, in most cases, must attach a completed federal income tax return to the application.⁹

Proving identity and foreign status requires original documents. A valid passport is the single document that satisfies both requirements. Without one, you need a combination of documents such as a national ID card, foreign birth certificate, or foreign voter registration card. To avoid mailing original passports to the IRS, you can visit an IRS-authorized Certifying Acceptance Agent, who verifies your documents in person and forwards certified copies with your application.

Applications go to the IRS processing center in Austin, Texas. Outside of filing season, the IRS estimates about seven weeks for processing. During peak filing season (January 15 through April 30), processing stretches to 9 to 11 weeks.¹⁰

Applying Without a Tax Return

Five exceptions let you apply for an ITIN without attaching a federal tax return:⁹

Passive income (rental income, dividends, royalties, annuity income, or partnership distributions) where a third party is withholding tax or you are claiming treaty benefits.
Wages, honoraria, fellowships, grants, or gambling income where you are claiming a tax treaty benefit. Noncompensatory scholarship or fellowship income subject to reporting or withholding also qualifies without a treaty claim.
Mortgage interest on U.S. real property where the lender reports the interest to the IRS.
Sale of U.S. real property by a foreign person when withholding applies under FIRPTA.
E-filing compliance for a non-U.S. representative of a foreign corporation.

If you are otherwise required to file a federal return, you cannot use the passive-income exception. You must attach the return to your W-7. Each exception has its own supporting documentation requirements, detailed in the Form W-7 instructions.

Expiration and Renewal

An ITIN that is not used on any U.S. federal tax return for three consecutive years expires automatically on December 31 of that third year.¹¹ Appearing on an information return like a Form 1099 does not count as use for this purpose. Only inclusion on a filed federal tax return resets the clock.

To renew, complete a new Form W-7, check the “Renew an existing ITIN” box, and submit updated identity documents. Spouses and dependents renewing to claim a tax benefit must attach a federal tax return listing them. Renewal applications follow the same process and timeline as new ITIN applications.¹¹

Switching to a Social Security Number

If you later become eligible for and receive an SSN, stop using your ITIN immediately and notify the IRS so it can merge your tax records under the new number. Using both numbers simultaneously is not allowed.¹² If you skip this step, wages and withholding reported under the old ITIN may not link to your SSN, which can reduce your refund or create compliance problems.

To notify the IRS, visit a local office or send a letter to the Internal Revenue Service at Austin, TX 73301-0057. Include your full name, mailing address, ITIN, a copy of your new Social Security card, and a copy of your CP 565 notice (the ITIN assignment letter) if you still have it. The IRS will void the ITIN and associate all prior filings with your SSN.¹²

Adoption Taxpayer Identification Number

Parents in the middle of a domestic adoption sometimes cannot get an SSN for the child before the tax filing deadline. An ATIN fills the gap. You apply using Form W-7A. The child must be a U.S. citizen or resident who was placed in your home for legal adoption by an authorized agency. Foster care placements do not qualify.¹³

Attach documentation proving the placement. Any one of the following typically satisfies the requirement: a signed placement agreement from the agency, a hospital release document authorizing the child’s release to you, a court order approving the placement, or an affidavit from the adoption attorney or government official who placed the child. Mail the completed form and documentation to the address in the Form W-7A instructions.

An ATIN expires two years after it is issued. The IRS sends a reminder three months before expiration with instructions for requesting an extension if the adoption is not yet final. While the ATIN is active, you can use it to claim the child as a dependent and claim the child and dependent care credit if otherwise eligible. You cannot use an ATIN to claim the Earned Income Tax Credit; the EITC requires an SSN.¹⁴ Once the adoption is finalized, apply for a permanent SSN for the child and stop using the ATIN.

Preparer Taxpayer Identification Number

Anyone who prepares tax returns for compensation must have a PTIN and include it on every return they file for clients.¹⁵ The number identifies the preparer personally, separate from any firm’s EIN, and lets the IRS track compliance history. You apply or renew through the IRS Tax Professional PTIN System online, providing personal identification, business information, and professional credentials.

The application and renewal fee is $18.75 for 2026.¹⁶ After you submit the online form, the number is issued almost immediately. PTINs expire on December 31 of the calendar year for which they are issued, so preparers must renew before each new filing season.¹⁷ Filing returns without a current PTIN can result in penalties against the preparer.

Protecting Your Taxpayer ID From Fraud

Tax-related identity theft happens when someone uses your SSN or ITIN to file a fraudulent return, usually to claim a refund. If a return has already been filed under your number, or you receive an IRS notice about income you did not earn, file Form 14039 (Identity Theft Affidavit). The preferred method is completing it online at irs.gov. You can also fax it to 855-807-5720 or mail it to the IRS in Fresno, CA 93725. Use only one submission method.¹⁸ If you are responding to a specific IRS notice, use the fax number or address on that notice instead.

For ongoing protection, the IRS offers an Identity Protection PIN (IP PIN) to anyone with an SSN or ITIN who can verify their identity.¹⁹ The IP PIN is a six-digit number that changes every year. You enter it on your return when you file, and any e-filed return submitted without the correct IP PIN will be rejected. Paper returns filed without it face extended processing delays while the IRS manually verifies your identity.²⁰ The fastest way to enroll is through your IRS online account. If you cannot verify your identity online and your adjusted gross income is below $84,000 (or $168,000 for married filing jointly), you can apply using Form 15227. Otherwise, visit a Taxpayer Assistance Center in person with two forms of identification. Parents and legal guardians can also request an IP PIN for dependents.

1
Office of the Law Revision Counsel. 26 USC 6109 – Identifying Numbers
2
Social Security Administration. Form SS-5 – Application for a Social Security Card
3
Social Security Administration. Replace Social Security Card
4
Social Security Administration. Who Can Be Assigned a Social Security Number
5
Internal Revenue Service. Instructions for Form SS-4
6
Internal Revenue Service. Get an Employer Identification Number
7
Internal Revenue Service. When to Get a New EIN
8
eCFR. 26 CFR 301.6109-1 – Identifying Numbers
9
Internal Revenue Service. Instructions for Form W-7
10
Internal Revenue Service. How to Apply for an ITIN
11
Internal Revenue Service. How to Renew an ITIN
12
Internal Revenue Service. Additional ITIN Information
13
Internal Revenue Service. Instructions for Form W-7A – Application for Taxpayer Identification Number for Pending U.S. Adoptions
14
Internal Revenue Service. Adoption Taxpayer Identification Number
15
eCFR. 26 CFR 1.6109-2 – Tax Return Preparers Furnishing Identifying Numbers
16
Internal Revenue Service. PTIN Top FAQ 4
17
Internal Revenue Service. IRS Reminds Tax Pros to Renew PTINs for the 2026 Tax Season
18
Internal Revenue Service. Identity Theft Affidavit – Form 14039
19
Internal Revenue Service. Get an Identity Protection PIN
20
Internal Revenue Service. FAQs About the Identity Protection Personal Identification Number