What Is a Tax ID Number? Types, Uses, and How to Apply

A tax ID number is the nine-digit identifier the IRS uses to track you or your business on federal tax filings, and federal law requires you to include one on every return, statement, or document you send the agency.¹ The formal name is Taxpayer Identification Number (TIN), and there are five kinds. Which one you need depends on who you are: an individual with work authorization, a business, a foreign filer, an adoptive parent, or a paid tax preparer.

The Five Types of Tax ID Numbers

Each TIN serves a different filer.

Social Security Number (SSN). Issued by the Social Security Administration to U.S. citizens and authorized residents. It tracks earnings for Social Security purposes and doubles as your federal tax ID.²
Employer Identification Number (EIN). The tax ID for businesses, tax-exempt organizations, trusts, and estates. Free from the IRS.³
Individual Taxpayer Identification Number (ITIN). For people who must file a federal return but aren’t eligible for an SSN, including certain foreign nationals and their dependents.⁴
Adoption Taxpayer Identification Number (ATIN). A temporary number for a child placed in your home for legal adoption when you can’t get their SSN in time to file. It expires two years after issuance.⁵
Preparer Taxpayer Identification Number (PTIN). Required for anyone who prepares federal tax returns for pay. It expires every December 31 and must be renewed each year; the 2026 renewal fee is $18.75.⁶

One boundary worth naming up front: an ITIN is a filing tool, nothing more. It does not authorize you to work in the United States, does not change your immigration status, and does not qualify you for Social Security benefits.⁷ ITIN holders also cannot claim the Earned Income Tax Credit. If either spouse on a joint return files with an ITIN, neither spouse can claim the EITC, even when the dependents have valid SSNs.⁸

When You Need a Tax ID Number

If you have an SSN, you already have a tax ID and most of the situations below don’t apply to you as an individual. You need a separate number when you start certain activities.

You’re hiring employees. Any business with employees needs an EIN to report withheld income taxes and Social Security and Medicare contributions.³
You’re forming a corporation, partnership, or LLC. These entities need their own EIN whether or not they have employees.³
You’re a sole proprietor in a U.S. trade or business. Even without employees, you need an EIN.⁹
You’re setting up a trust, estate, or retirement plan. Each needs its own EIN.³
You must file but can’t get an SSN. Foreign nationals with a U.S. tax obligation apply for an ITIN.¹⁰
You’re adopting a U.S. child. If you can’t obtain the child’s SSN before your return is due, apply for an ATIN.⁵
You’re opening an interest-bearing bank account. Banks must report interest to the IRS and will ask for your TIN. Without one, the bank may apply backup withholding to your interest.¹¹

How to Apply

The form, submission method, and processing time depend on which TIN you need.

Social Security Number

Most U.S. citizens receive an SSN at birth through hospital paperwork. If you need a new or replacement card, you can apply online at the SSA’s website or at a local Social Security office. The card usually arrives within 10 business days.¹²

Employer Identification Number

The fastest route is the IRS online EIN tool, which issues your number immediately on submission. There is no fee. The IRS warns that any website charging for an EIN is not an official government service.¹³

If you’d rather apply by mail, file Form SS-4. Mailed applications take about four to five weeks. The form asks for the entity’s legal name, the responsible party’s name and SSN or ITIN, the entity type, and the reason for applying.¹⁴ International applicants whose principal place of business is outside the U.S. can’t use the online tool; they apply by phone, fax, or mail using Form SS-4.³

Individual Taxpayer Identification Number

Complete Form W-7 and submit it with your federal tax return, unless you qualify for an exception. You must include documents that prove both your identity and your foreign status.¹⁵ A valid passport is the simplest option because it’s the only standalone document. Without one, you’ll need at least two documents, and at least one must have a photo.¹⁶

Everything you submit must be an original or a certified copy from the issuing agency. Regular photocopies aren’t accepted. You have three submission options: mail the W-7 with your return and original documents to the IRS ITIN Operation in Austin, Texas; take it to an IRS Taxpayer Assistance Center in person; or use a Certifying Acceptance Agent, who can authenticate most of your documents in person so you don’t have to mail originals. Processing takes about seven weeks in ordinary times, and nine to eleven during tax season (January 15 through April 30) or for applicants abroad.¹⁷

Adoption Taxpayer Identification Number

Complete Form W-7A and mail it to the IRS. Attach documentation showing that the child was placed in your home for legal adoption by an authorized placement agency: a placement agreement, court order, or a hospital official’s signed document all qualify. The child must be a U.S. citizen or resident alien. If the child is a foreign national, file Form W-7 for an ITIN instead. Processing takes four to eight weeks, so apply well before you need to file. Once the adoption is final and the child receives an SSN, stop using the ATIN and switch to the SSN on future returns.⁵

Preparer Taxpayer Identification Number

Anyone who prepares federal returns for pay must have a PTIN before signing a return. Apply or renew through the IRS online PTIN system. The 2026 fee is $18.75, and the number expires every December 31, so you’ll renew before each filing season.⁶

ITIN Expiration and Renewal

SSNs and EINs don’t expire, but ITINs can. If you don’t include your ITIN on a federal tax return for three consecutive years, it expires on December 31 after the third year of non-use. An expired ITIN can still be used on information returns like a 1099, so renewal is only necessary if you’ll put the number on a federal tax return.¹⁸

To renew, file a new Form W-7 and check the “Renew an existing ITIN” box. A renewal-only application doesn’t need a tax return attached, but spouses and dependents renewing to claim an allowable tax benefit must be listed on an attached return. Include documentation for any legal name change, such as a marriage certificate or court order. Family members on the same return can renew together in one package.¹⁸

Penalties for a Missing or Wrong Tax ID

For individuals, the practical consequence of not providing your TIN to a bank or other payer that requests it is backup withholding: the payer must withhold a percentage of your payments and send it to the IRS.¹¹

For businesses filing information returns like the 1099, a missing or incorrect TIN triggers per-return penalties that scale with how long you take to correct it. For returns due in 2026, the penalty is $60 per return if corrected within 30 days, $130 if corrected by August 1, and $340 if not corrected after August 1. Intentional disregard costs $680 per return with no annual cap.¹⁹

Protecting Your Tax ID

A stolen tax ID can be used to file fraudulent returns or open accounts in your name. The IRS offers a free Identity Protection PIN (IP PIN), a six-digit number that blocks anyone else from filing a federal return using your SSN or ITIN. Anyone who can verify their identity is eligible, and parents or guardians can request one for a dependent.²⁰

The fastest way to get one is through your IRS online account. If you can’t create an online account and your adjusted gross income is below $84,000 ($168,000 for married filing jointly), you can file Form 15227; the IRS will verify your identity by phone and mail your IP PIN in four to six weeks. You can also visit a Taxpayer Assistance Center in person with a government-issued photo ID and one additional form of identification.²⁰

If you suspect someone is using your business name or EIN to file fraudulent returns or W-2s, submit Form 14039-B, the Business Identity Theft Affidavit. Warning signs include a rejection notice for an electronically filed return because the IRS already has one on file, or a notice about a balance you don’t owe.²¹

Closing an EIN You No Longer Need

Once assigned, an EIN becomes the entity’s permanent federal tax ID and is never reassigned to another entity.²² The IRS can’t cancel the number, but it can deactivate the account. Send a letter to the IRS with the business’s legal name, EIN, business address, and the reason for closing. If you still have the original EIN assignment notice, include a copy. Mail everything to the Internal Revenue Service in Cincinnati, OH 45999. The IRS won’t close the account until all required returns are filed and all taxes owed are paid.²³

1
Office of the Law Revision Counsel. 26 USC 6109 – Identifying Numbers
2
Social Security Administration. The Story of the Social Security Number
3
Internal Revenue Service. Employer Identification Number
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eCFR. 26 CFR 301.6109-1 – Identifying Numbers
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Internal Revenue Service. Instructions for Form W-7A
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Internal Revenue Service. IRS Reminds Tax Pros to Renew PTINs for the 2026 Tax Season
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Internal Revenue Service. Individual Taxpayer Identification Number (ITIN)
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Internal Revenue Service. Individual Taxpayer Identification Number (ITIN) Reminders for Tax Professionals
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Internal Revenue Service. U.S. Taxpayer Identification Number Requirement
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Internal Revenue Service. Topic No. 857 – Individual Taxpayer Identification Number (ITIN)
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Internal Revenue Service. Topic No. 403 – Interest Received
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Social Security Matters (SSA). A Faster and More Convenient Way to Request a Social Security Number and Card
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Internal Revenue Service. Get an Employer Identification Number
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Internal Revenue Service. Instructions for Form SS-4
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Internal Revenue Service. Instructions for Form W-7
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Internal Revenue Service. ITIN Supporting Documents
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Internal Revenue Service. How to Apply for an ITIN
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Internal Revenue Service. How to Renew an ITIN
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Internal Revenue Service. Information Return Penalties
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Internal Revenue Service. Get an Identity Protection PIN
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Internal Revenue Service. Report Identity Theft for a Business
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Internal Revenue Service. If You No Longer Need Your EIN
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Internal Revenue Service. Closing a Business