What Is a Tax Identification Number and How Do You Get One?

A tax identification number is a unique number the IRS uses to track a person or entity for federal tax purposes, and federal law requires one on every return you file.¹ There are five kinds, and the one you need depends on who you are and why you are filing. Pick the wrong one, or leave the field blank, and you can face a per-failure penalty and automatic withholding on your income.

The Five Types

Social Security Number (SSN): the number the Social Security Administration issues to U.S. citizens and to noncitizens authorized to work or study in the country. For most individuals, this is their tax ID.²
Employer Identification Number (EIN): a nine-digit number the IRS assigns to businesses, tax-exempt organizations, estates, and trusts.³
Individual Taxpayer Identification Number (ITIN): a nine-digit number for people who must file a federal return but cannot get an SSN. An ITIN does not authorize work in the United States and does not qualify you for Social Security benefits.⁴
Adoption Taxpayer Identification Number (ATIN): a temporary number for a child placed for domestic adoption when the adoptive parents cannot yet obtain an SSN for the child.⁵
Preparer Taxpayer Identification Number (PTIN): an eight-digit number preceded by the letter “P,” required for anyone who prepares or helps prepare federal tax returns for compensation.⁶

Which Number You Need

Individuals

If you are a U.S. citizen or an authorized noncitizen, your SSN doubles as your tax ID for nearly every purpose. You will only need a separate number if you run a business that requires an EIN.

If you are a resident alien, a nonresident alien, or the spouse or dependent of either, and you are not eligible for an SSN, you need an ITIN to file a federal return. Common reasons for applying include claiming a tax treaty benefit, filing based on the substantial presence test (more than 183 days in the U.S.), or being listed as a dependent on someone else’s return.⁴

Businesses and Organizations

You need an EIN if you hire employees, operate as a partnership, corporation, or LLC, or run a tax-exempt organization, estate, or trust.³ Sole proprietors with no employees who file on Schedule C can generally use their SSN, though many still get an EIN to keep their SSN off invoices and business paperwork.

Adoptive Parents

An ATIN is only for the narrow case where a child has been legally placed in your home for a domestic adoption and you cannot yet get the child’s SSN. You have to have tried, and the SSA has to be unwilling to issue a new number — typically because the adoption is not final.⁵ A foreign adoption qualifies only if the child already has a Permanent Resident Alien Card or Certificate of Citizenship. One boundary worth flagging: an ATIN cannot be used to claim the Earned Income Tax Credit; only an SSN qualifies for that credit.

Paid Tax Preparers

Anyone paid to prepare or help prepare federal returns must have a current PTIN. Renewal opens in mid-October each year for the following filing season, and the fee for 2026 is $18.75.⁶

Getting an EIN

Applying for an EIN is free. The fastest route is the IRS online application, which issues the number immediately on approval.⁷ The responsible party for the entity must have a valid SSN or ITIN to use the online tool, and the IRS limits each responsible party to one EIN per day.

If online is not an option, file Form SS-4 by mail or fax.⁸ You will need the entity’s legal name as it appears on the formation document, the name and SSN or ITIN of the responsible party, and the entity type (corporation, partnership, sole proprietorship, trust, and so on).⁹

Be wary of third-party sites that charge a fee to obtain an EIN for you. The IRS issues EINs at no cost, and the official application lives on IRS.gov.

Getting an ITIN

To apply for an ITIN, submit Form W-7 with your federal tax return and documents proving both your identity and your foreign status.¹⁰ A valid passport is the only single document that meets both requirements on its own. Without a passport, you must provide at least two documents from the IRS-approved list, such as a national ID card and a birth certificate.¹¹

There are three ways to submit the application:

By mail to the IRS ITIN Operation in Austin, Texas. Send Form W-7, your return, and original or certified identity documents. The IRS returns the documents after processing.
In person at an IRS Taxpayer Assistance Center that offers ITIN services. Staff verify your originals on the spot so you do not have to mail them, and there is no fee.¹⁰
Through a Certifying Acceptance Agent (CAA). A CAA can verify your passport and birth certificate in person and hand them back immediately, then forward the application. CAAs charge a fee that varies by provider.¹²

Processing runs about seven weeks under normal conditions, and nine to eleven weeks if you apply during the peak period from January 15 through April 30 or if you apply from overseas.¹¹ Once approved, the IRS mails a notice with your ITIN to the address on the application.

Getting an ATIN

Adoptive parents file Form W-7A with a copy of the placement documentation to the IRS Austin Service Center, and should apply at least eight weeks before the return is due. Once the adoption is final, you must obtain an SSN for the child and notify the IRS. Fail to notify within two years and the ATIN is automatically deactivated.⁵

Keeping the Number Valid

ITINs expire from disuse. If yours is not used on a federal return for three consecutive tax years, it expires on December 31 after that third year.¹³ To renew, submit a new Form W-7 with current identity documents. You do not need to attach a tax return for a renewal. Filing with an expired ITIN can delay your refund and temporarily block certain credits, so check the status before filing season if you have been out of the system for a while.

PTINs work on a different clock: they expire every December 31 and have to be renewed annually.⁶ EINs and SSNs do not expire.

What Happens If You Don’t Provide One

When a TIN is required on a return or other document and you fail to include it, the IRS can impose a $50 penalty for each failure, capped at $100,000 per calendar year.¹⁴ The amount is not adjusted for inflation. The penalty is waived if you can show reasonable cause.

The faster consequence hits when you fail to give a correct TIN to a bank, brokerage, or other payer. That payer must then withhold 24 percent of your reportable payments, including interest and dividends, and send it to the IRS instead of paying it to you.¹⁵ This is called backup withholding, and it continues until you supply a correct TIN. You can claim the withheld amount as a credit when you file, but you lose use of the money in the meantime.

1
Office of the Law Revision Counsel. 26 U.S.C. 6109 – Identifying Numbers
2
Social Security Administration. Request a Social Security Number for the First Time
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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. Frequently Asked Questions: PTIN Application/Renewal Assistance
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Internal Revenue Service. Get an Employer Identification Number
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Internal Revenue Service. About Form SS-4, Application for Employer Identification Number (EIN)
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Internal Revenue Service. Instructions for Form SS-4 (Rev. December 2025)
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Internal Revenue Service. How to Apply for an ITIN
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Internal Revenue Service. Instructions for Form W-7 (Rev. December 2024)
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Internal Revenue Service. ITIN Acceptance Agents
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Internal Revenue Service. How to Renew an ITIN
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Office of the Law Revision Counsel. 26 U.S.C. 6723 – Failure to Comply With Other Information Reporting Requirements
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Internal Revenue Service. Backup Withholding