What Is a Tax ID Number and Which One Do You Need?

A tax ID number is a nine-digit number the IRS uses to identify you on tax returns and match income reported under your name or business. The IRS recognizes five kinds, and the one you need depends on whether you’re a U.S. citizen, a noncitizen, a business, an adopting parent, or a paid tax preparer. Most applications are free and can be done online or by mail.¹

The Five Types of Tax ID Numbers

Federal law requires anyone who files a tax return or appears on a tax document to have an identifying number.² The IRS issues or recognizes five:¹

Social Security Number (SSN), issued by the Social Security Administration to U.S. citizens and noncitizens authorized to work. This is the default TIN for most individuals.
Employer Identification Number (EIN), used by businesses, nonprofits, trusts, and estates for payroll, entity-level tax filings, and business bank accounts.³
Individual Taxpayer Identification Number (ITIN), for resident and nonresident aliens, their spouses, and their dependents who have a federal tax filing obligation but aren’t eligible for an SSN.⁴
Adoption Taxpayer Identification Number (ATIN), a temporary number for a child in a pending domestic adoption (or a foreign adoption where the child has a Permanent Resident Alien Card) when the adoptive parents can’t yet obtain an SSN for the child.⁵
Preparer Taxpayer Identification Number (PTIN), required for anyone paid to prepare federal tax returns. A PTIN is eight digits preceded by the letter “P.”⁶

Which One You Need

If you’re a U.S. citizen or permanent resident, your SSN handles nearly all personal tax filing. You don’t need any other TIN unless you start a business or prepare taxes professionally.

If you’re a noncitizen authorized to work in the United States, you qualify for an SSN. You’ll need to show the Social Security Administration proof of your work-authorized immigration status, such as a Permanent Resident Card (Form I-551), an Employment Authorization Document (Form I-766), or an Arrival/Departure Record (Form I-94) reflecting an admission class that permits work.⁷ If you aren’t authorized to work but still have a federal tax filing requirement, you need an ITIN instead.

If you own a business, you need an EIN when you operate as a corporation, partnership, LLC, or nonprofit, or when you hire employees. Sole proprietors can use an SSN for simple operations, but getting an EIN keeps your SSN off invoices and W-9 forms and is required once you take on payroll or open a business bank account.³

How to Apply for an EIN

You apply using IRS Form SS-4. The form asks for the entity’s legal name, its type, and the name and SSN or ITIN of a “responsible party,” meaning the person who ultimately owns or controls the entity and its funds. For a single-member LLC, that’s you. For a partnership, it’s typically a managing partner.⁸

The fastest route is the IRS online application, which issues the EIN at the end of the session. The tool is available Monday through Friday from 6:00 a.m. to 1:00 a.m. Eastern, Saturday from 6:00 a.m. to 9:00 p.m., and Sunday from 6:00 p.m. to midnight.⁹ To use it, you need a legal residence or principal place of business in the United States or U.S. territories. If you’re outside the U.S. or prefer paper, you can fax Form SS-4 and get your EIN within about four business days, mail the form and wait four to five weeks, or, as an international applicant, apply by phone.⁸

One order-of-operations detail matters. If you’re forming an LLC, corporation, or other legal entity, register the entity with your state before applying for the EIN. The IRS expects the entity to already exist when you submit Form SS-4.⁹

How to Apply for an ITIN

You apply using IRS Form W-7. The form asks for your name, foreign address, immigration status, and reason for applying. You must also provide documents proving both your identity and your foreign status. A valid passport works as a standalone document. Without a passport, you need at least two documents from the IRS’s accepted list, and at least one must include a photograph.¹⁰

There are four ways to submit:¹¹

Mail Form W-7, your tax return, and original documents (or certified copies from the issuing agency) to the IRS ITIN Operation in Austin, Texas. Processing takes about seven weeks, or nine to eleven weeks from January 15 through April 30. The IRS returns your originals after processing.¹⁰
Visit an IRS Taxpayer Assistance Center that offers ITIN services. Free, and you don’t mail your originals.
Use a Certifying Acceptance Agent, who can verify your documents in person and return them the same day. CAAs charge a fee that varies by provider.¹²
Use a Volunteer Income Tax Assistance (VITA) site that handles ITIN applications during tax season, at no cost.

The main practical issue with the mail route is being without your original passport or birth certificate for weeks. If that’s a problem, use a Taxpayer Assistance Center or a CAA.

What an ITIN Does Not Do

An ITIN is strictly a tax-filing number. It does not authorize you to work in the United States, and it does not make you eligible for Social Security benefits.¹³ An employer asking for proof of work authorization won’t accept an ITIN letter; that requires an SSN tied to valid work authorization from the Department of Homeland Security.

ITIN Expiration and Renewal

An ITIN expires if you don’t use it on a federal tax return for three consecutive years. Expiration takes effect on December 31 after that third year of non-use.¹⁴ Separately, the IRS has already phased out all ITINs with middle digits in the ranges 70–88, 90–92, and 94–99, regardless of recent use. If your ITIN falls in one of those ranges, it must be renewed before you file again.

To renew, use Form W-7 again and check the “Renew an existing ITIN” box at the top. Provide your old ITIN if you have it and fresh identity documents. If your name has changed, include a marriage certificate or court order supporting the change. The same four submission routes apply.¹⁴

ATIN and PTIN

Adoption Taxpayer Identification Number

If you’re adopting a child and need to claim the child as a dependent before an SSN can be issued, apply for an ATIN using Form W-7A. You qualify only when the child has been legally placed in your home by an authorized agency, you’ve made a reasonable effort to obtain the child’s existing SSN, and the SSA can’t issue a new one yet because the adoption isn’t final.⁵ Mail Form W-7A and your placement documentation to the IRS Austin Service Center, or drop it off at an IRS walk-in office. Once the adoption is final, get the child an SSN and notify the IRS. Otherwise the ATIN automatically deactivates after two years.

Preparer Taxpayer Identification Number

Anyone paid to prepare federal tax returns needs a PTIN. Most first-time applicants can obtain one online in about 15 minutes. The fee is $18.75 for both new applications and annual renewals, payable by credit card, debit card, or electronic check. If you prefer paper, file Form W-12 with payment to the IRS PTIN Processing Center and expect about six weeks.⁶

What Happens If You Don’t Have a Valid TIN

Failing to give a valid TIN to a bank, brokerage, or other payer triggers backup withholding: the payer must withhold 24% of your payments and send it to the IRS.¹⁵ You can recover it by filing a return, but the cash-flow hit is immediate.

On the reporting side, failing to comply with information reporting requirements that call for a TIN can carry a $50 penalty per failure, up to $100,000 per calendar year.¹⁶ For a business that needs an EIN, operating without one means wages can’t be properly reported and employment taxes can’t be withheld correctly, which invites much larger IRS problems.

Fees and Scams

Applying for an EIN directly through the IRS is always free. The IRS warns against third-party sites that charge for this service.⁹ Those sites often rank high in search results and charge anywhere from $50 to several hundred dollars for something you can do yourself in minutes at IRS.gov. If the URL doesn’t end in “.gov,” it isn’t the IRS.

ITIN applications are also free by mail, at an IRS Taxpayer Assistance Center, or at a VITA site. Only Acceptance Agents and Certifying Acceptance Agents charge, and their fees vary.¹¹ Unsolicited offers to help with a tax ID application, pressure for personal information, or unusually large fees are all warning signs. The IRS does not initiate contact by email, text, or social media to offer help with TIN applications.¹⁷

1
Internal Revenue Service. Taxpayer Identification Numbers (TIN)
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Office of the Law Revision Counsel. 26 USC 6109 – Identifying Numbers
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Internal Revenue Service. Employer Identification Number
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Internal Revenue Service. Individual Taxpayer Identification Number (ITIN)
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Internal Revenue Service. Adoption Taxpayer Identification Number
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Internal Revenue Service. PTIN Requirements for Tax Return Preparers
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Social Security Administration. Social Security Numbers For Noncitizens
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Internal Revenue Service. Instructions for Form SS-4
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Internal Revenue Service. Get an Employer Identification Number
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Internal Revenue Service. Instructions for Form W-7
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Internal Revenue Service. How to Apply for an ITIN
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Internal Revenue Service. ITIN Acceptance Agents
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Internal Revenue Service. Individual Taxpayer Identification Number (ITIN) Reminders for Tax Professionals
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Internal Revenue Service. How to Renew an ITIN
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Internal Revenue Service. Backup Withholding
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Office of the Law Revision Counsel. 26 USC 6723 – Failure to Comply With Other Information Reporting Requirements
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Internal Revenue Service. Tax Scams