A tax ID number is a nine-digit identifier the Internal Revenue Service uses to track individuals and entities within the federal tax system. Federal law requires anyone who files a return, claims a treaty benefit, or appears on someone else’s tax documents to have one.1Office of the Law Revision Counsel. 26 USC 6109 Identifying Numbers Five different types exist, and which one you need depends on whether you’re an individual, a business, a foreign national with a U.S. tax obligation, an adopting parent, or a paid tax preparer.
The Five Types and Who Uses Each
Social Security Number
The Social Security Number (SSN) is the most common tax ID. The Social Security Administration issues SSNs to U.S. citizens and to noncitizens authorized to work, attend school, or with another valid nonwork reason.2Social Security Administration. Request Social Security Number for the First Time If you already have an SSN, that number is your tax ID on personal returns. No separate IRS application is needed.
Employer Identification Number
An Employer Identification Number (EIN) is the business equivalent of an SSN. The IRS assigns EINs to partnerships, corporations, LLCs, nonprofits, trusts, and estates.3Internal Revenue Service. Employer Identification Number Even a sole proprietor needs one if they have employees, withhold taxes on payments to nonresident aliens, or owe excise taxes.
Sole proprietors without employees can legally use their SSN, but many apply for an EIN anyway. It keeps your SSN off W-9s, invoices, and 1099s, which cuts identity-theft exposure, and it lets you open a business bank account and build business credit separate from your personal file.
Individual Taxpayer Identification Number
If you have a federal tax obligation but aren’t eligible for an SSN, the IRS issues an Individual Taxpayer Identification Number (ITIN). It covers foreign nationals, resident aliens, and their spouses or dependents who need to file a return or claim a treaty benefit.4Internal Revenue Service. Individual Taxpayer Identification Number ITIN An ITIN is strictly for federal tax purposes. It does not authorize work in the United States, does not qualify you for Social Security benefits, and does not affect your immigration status.5Internal Revenue Service. Topic No 857 Individual Taxpayer Identification Number ITIN
Adoption Taxpayer Identification Number
An Adoption Taxpayer Identification Number (ATIN) is a temporary number for a child placed in your home for legal adoption when you can’t yet get an SSN for that child. That may be because the adoption isn’t final, or because the birth parents won’t share an existing number.6eCFR. 26 CFR 301.6109-3 IRS Adoption Taxpayer Identification Numbers It lets you claim the child as a dependent while the adoption is pending. The ATIN expires automatically two years after issuance, and you apply using Form W-7A.7Internal Revenue Service. Adoption Taxpayer Identification Number
Preparer Tax Identification Number
Anyone who prepares federal tax returns for pay must get a Preparer Tax Identification Number (PTIN) from the IRS before touching a client return. The PTIN goes in the “Paid Preparer” section of every return you complete.8Internal Revenue Service. Frequently Asked Questions Do I Need a PTIN It renews yearly. The 2026 renewal fee is $18.75.9Internal Revenue Service. PTIN Requirements for Tax Return Preparers
When You’ll Be Asked for a Tax ID
Almost every interaction with the federal tax system requires one. The common triggers:
- Filing an annual return or claiming a tax credit. A valid tax ID must appear on the return.1Office of the Law Revision Counsel. 26 USC 6109 Identifying Numbers
- Forming a business entity. Partnerships, corporations, LLCs, and nonprofits need an EIN, as do sole proprietors with employees.3Internal Revenue Service. Employer Identification Number
- Hiring employees. The EIN is used to report wages and withhold federal income tax and Social Security contributions on Form W-2.10Internal Revenue Service. About Form W-2 Wage and Tax Statement
- Working as an independent contractor. Clients ask you to complete a Form W-9 with your SSN or EIN so they can issue a 1099-NEC.11Internal Revenue Service. Form W-9 Request for Taxpayer Identification Number and Certification
- Opening a bank account. Financial institutions need a tax ID to report interest to the IRS.
- Registering for state taxes. Most states with income or employment taxes require a separate state tax ID on top of your federal EIN. Processes vary by state.12U.S. Small Business Administration. Get Federal and State Tax ID Numbers
How to Get an EIN
The fastest route is the online application at irs.gov. You get the number immediately after finishing the questionnaire. The online tool 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.13Internal Revenue Service. Get an Employer Identification Number To use it, your principal place of business must sit in the United States or a U.S. territory.
International applicants apply by calling 267-941-1099, Monday through Friday, 6:00 a.m. to 11:00 p.m. Eastern.3Internal Revenue Service. Employer Identification Number You can also fax Form SS-4 to 855-641-6935 domestically or 304-707-9471 from abroad and expect your EIN back in about four business days.14Internal Revenue Service. Instructions for Form SS-4 Mailing is the slowest option at four to six weeks.
Form SS-4 asks for the entity’s legal name exactly as it appears on the organizing document, the entity type, both a mailing address and the physical business location, and a “responsible party” — the individual who ultimately owns or controls the entity — who must provide their own SSN or ITIN. Outside of government entities, the responsible party must be a person, not another business.14Internal Revenue Service. Instructions for Form SS-4
How to Get an ITIN
Complete Form W-7 and mail it with your supporting identity documents and the federal tax return it belongs to, to the IRS ITIN Operation in Austin, Texas. You can send originals or certified copies from the issuing agency. Processing takes about seven weeks, or nine to eleven weeks if you apply during peak filing season (January 15 through April 30) or from overseas.15Internal Revenue Service. Instructions for Form W-7
A valid passport is the only single document that proves both identity and foreign status. Without one, you need at least two documents from the IRS’s accepted list, such as a national ID card paired with a birth certificate.15Internal Revenue Service. Instructions for Form W-7 The form also asks why you’re applying — filing a return, claiming a treaty benefit, and so on — and a return generally must be attached unless an exception applies.
If you’d rather not mail original documents, apply in person at an IRS Taxpayer Assistance Center or work through an IRS-authorized Certifying Acceptance Agent, who can verify your documents and forward the application for you.
Keeping an ITIN Active
An ITIN expires on December 31 of the third consecutive year it isn’t used on a federal tax return. If your last use was on a 2022 return and you didn’t use it for 2023, 2024, or 2025, it expires at the end of 2025.16Internal Revenue Service. How to Renew an ITIN
To renew, submit a new Form W-7 with the “Renew an existing ITIN” box checked and current identity documents. Filing with an expired ITIN can delay your refund and block certain credits until the renewal clears.16Internal Revenue Service. How to Renew an ITIN If your ITIN only shows up on information returns sent to you, such as a 1099, you don’t need to renew it.
What Happens if the Number Is Missing or Wrong
Not providing a valid tax ID to a bank, brokerage, or other payer required to file an information return triggers backup withholding: the payer must send 24 percent of your payments to the IRS.17Internal Revenue Service. Tax Withholding Types You can reclaim that money when you file, but it’s out of your hands in the meantime.
Businesses that leave incorrect tax IDs on information returns face per-return penalties. For returns due in 2026, penalties run from $60 per return if corrected within 30 days, to $340 per return if never filed, up to $680 per return for intentional disregard.18Internal Revenue Service. Information Return Penalties
Protecting Your Tax ID
Your tax ID is the key to your IRS account, so a stolen number can let someone file a fraudulent return in your name and collect your refund. The IRS offers an Identity Protection PIN, a six-digit number that changes each year and must appear on your return. Once you opt in through your IRS online account, the IRS won’t process a return under your SSN or ITIN without the correct PIN.19Internal Revenue Service. Get an Identity Protection PIN
Basic hygiene helps too. Don’t share your SSN unless legally required, use an EIN in place of your SSN on business forms when you can, and shred anything with your tax ID on it before throwing it out.