What Is a Tax ID Number? EIN, SSN, ITIN Explained (2026)

A tax identification number (TIN) — commonly called a tax ID — is a unique number used by the IRS to track taxpayers. Every person and business that files taxes, earns income, or has a reporting obligation in the United States needs some form of tax ID. But which one do you need? Here’s the complete breakdown.

What Is a Tax ID?

A tax ID number (also called a tax identification number or TIN) is a 9-digit number assigned by the IRS or Social Security Administration that identifies you for tax purposes. There are three main types: SSN for individuals, EIN for businesses, and ITIN for non-citizens who need to file.

The IRS uses your tax ID to match your income (from W-2s, 1099s, K-1s) with your tax return. Banks, employers, and financial institutions also require your tax ID for reporting purposes.

Types of Tax ID Numbers

SSN (Social Security Number)

Your Social Security Number is the most common tax ID for U.S. citizens and permanent residents. It’s a 9-digit number (XXX-XX-XXXX) issued by the Social Security Administration (SSA), typically at birth or when you become eligible to work in the United States.

Used for: Personal tax returns (Form 1040), W-2 employment, opening bank accounts, applying for credit, and Social Security benefits.

How to get one: Apply at your local SSA office with proof of identity, age, and citizenship/immigration status. Parents typically apply for their child’s SSN along with the birth certificate. Processing takes 2–4 weeks.

EIN (Employer Identification Number)

An EIN (also called a Federal Tax ID Number or Federal Employer Identification Number / FEIN) is a 9-digit number (XX-XXXXXXX) assigned by the IRS to identify business entities. Think of it as a Social Security Number for your business.

You need an EIN if you:

• Have employees (any business with W-2 workers)
• Operate as a corporation, partnership, LLC with multiple members, or nonprofit
• File employment tax returns, excise tax returns, or alcohol/tobacco/firearms returns
• Withhold taxes on income paid to a non-resident alien
• Have a Keogh plan (a retirement plan for self-employed individuals)
• Are involved with trusts, estates, real estate mortgage investment conduits, or farmers’ cooperatives

Sole proprietors without employees are not required to get an EIN — they can use their SSN on Schedule C. However, many sole proprietors obtain an EIN anyway to keep their SSN private on invoices, W-9 forms, and business documents, and to open a separate business bank account.

ITIN (Individual Taxpayer Identification Number)

An ITIN is a tax processing number for individuals who are required to have a U.S. taxpayer identification number but are not eligible for an SSN. ITINs begin with the number “9” and follow the format 9XX-XX-XXXX.

Used by: Non-resident aliens who must file a U.S. tax return, resident aliens (based on days present) who file returns, dependents or spouses of U.S. citizens/resident aliens, and dependents or spouses of non-resident alien visa holders.

Important: An ITIN does not authorize work in the United States, does not provide eligibility for Social Security benefits, and does not qualify a dependent for the Earned Income Tax Credit.

How to get one: File Form W-7 with the IRS, along with your federal tax return and original identity documents (or certified copies). Processing takes 7–11 weeks. You can also apply through IRS-authorized Certifying Acceptance Agents.

How to Get an EIN (Free)

Getting an EIN is completely free and takes just minutes online. Here’s how to obtain an EIN:

Online Application (Recommended)

1. Go to the IRS EIN Online Application
2. Available Monday through Friday, 7:00 a.m. to 10:00 p.m. Eastern Time
3. Answer questions about your business structure, reason for applying, and responsible party
4. You receive your EIN immediately upon completion — no waiting
5. Download and save your confirmation notice (CP 575)

You must have a valid SSN or ITIN to be the “responsible party” on the application. Each responsible party can receive only one EIN per day.

By Fax

Complete IRS Form SS-4 (Application for Employer Identification Number) and fax it to the appropriate IRS fax number based on your location. You’ll receive your EIN within 4 business days via return fax.

By Mail

Mail the completed Form SS-4 to the IRS. Processing takes 4–5 weeks. This method is not recommended unless you cannot apply online or by fax.

By Phone (International Applicants Only)

Call the IRS Business & Specialty Tax Line at 267-941-1099 (not toll-free) Monday through Friday, 6:00 a.m. to 11:00 p.m. Eastern Time. This option is only available for applicants outside the United States.

Never pay for an EIN. Some websites charge fees to “help” you apply for an EIN. The IRS issues EINs for free. Always apply directly through irs.gov.

How to Find Your Existing EIN

Lost your EIN? Here are several ways to find it:

1. EIN confirmation letter (CP 575): The IRS mails this when your EIN is first assigned. Check your business records.
2. Previous tax returns: Your EIN appears on every business tax return you’ve filed (Form 1120, 1065, 1120-S, Schedule C, etc.).
3. Bank records: Any bank where you opened a business account has your EIN on file. Contact the bank’s business banking department.
4. State business registration: If you registered your business with your state, your EIN may be on the registration documents.
5. Call the IRS: The Business & Specialty Tax Line at 1-800-829-4933 (Monday–Friday, 7:00 a.m. to 7:00 p.m. local time) can look up your EIN after verifying your identity. Only authorized individuals (officers, partners, or sole proprietors) can request this information.
6. IRS verification letter (147C): You can request a 147C letter from the IRS that confirms your EIN, which is useful for bank account openings or other verifications.

When Do You Need Which Tax ID?

Situation	ID Needed	How to Get
Filing personal taxes	SSN	SSA office
Starting a sole proprietorship (no employees)	SSN or EIN	IRS.gov (optional)
Starting an LLC or corporation	EIN	IRS.gov (required)
Hiring employees	EIN	IRS.gov (required)
Opening a business bank account	EIN	IRS.gov
Freelancing / 1099 work	SSN or EIN	EIN optional but recommended
Non-citizen filing US taxes	ITIN	Form W-7
Creating a trust or estate	EIN	IRS.gov
Nonprofit organization	EIN	IRS.gov

Frequently Asked Questions

Can I use my SSN instead of an EIN? Yes, if you’re a sole proprietor with no employees. However, an EIN provides better identity protection since you won’t need to share your SSN with clients who request a W-9.

Can one person have multiple EINs? Yes — each separate business entity gets its own EIN. A person who owns an LLC, a corporation, and a sole proprietorship would have three different EINs.

Does an EIN expire? No. Once issued, an EIN is permanent and belongs to that entity forever, even if the business closes. A closed business’s EIN is never reissued to another entity.

Use our tax calculator to estimate your federal tax liability, or the self-employment tax calculator if you’re filing with an EIN as a sole proprietor or freelancer.