What Is a Tax ID? SSN, EIN, ITIN, PTIN Explained

A “tax ID” is any identification number the IRS uses to track a taxpayer. There are five main types in the US, each for a different purpose. Knowing which you need depends on your situation: individual taxpayer, business owner, foreign person, or tax preparer.

The five tax IDs:

Tax ID type	Used by	Format	Issued by
SSN (Social Security Number)	US individuals	123-45-6789	Social Security Administration
EIN (Employer Identification Number)	Businesses & entities	12-3456789	IRS
ITIN (Individual Taxpayer Identification Number)	Non-resident foreigners with US tax obligations	9XX-XX-XXXX (starts with 9)	IRS
ATIN (Adoption Taxpayer Identification Number)	Adopted children pending SSN	Same format as SSN	IRS
PTIN (Preparer Tax Identification Number)	Paid tax preparers	P-XXXXXXXX	IRS

The most common tax ID. Issued automatically to US citizens at birth and to lawful permanent residents (green card holders) when they get authorized to work.

Used for:

Filing personal income tax (Form 1040)
W-2 wages and 1099 income reporting
Opening US bank accounts
Credit applications
Most government benefits

How to get one:

US citizens: at birth (parents file SS-5 with hospital paperwork)
Lawful permanent residents: file SS-5 with green card and ID
Some authorized non-immigrants: file SS-5 with work authorization

You only get one SSN for life. The number doesn’t change even after legal name change.

2. Employer Identification Number (EIN)

A 9-digit number identifying a business or organization. Sometimes called a “federal tax ID number.”

Who needs one:

Businesses with employees
Corporations and partnerships (even single-member LLCs treated as corporations)
Trusts and estates
Nonprofits and churches
Retirement accounts (IRA, 401k)
Anyone who needs to file business tax returns

Sole proprietors: You can use your SSN for business taxes, BUT having an EIN is recommended for:

Privacy (don’t share SSN on contracts)
Opening business bank accounts
Having employees
1099-NEC filing

How to get an EIN:

Online at IRS.gov (immediate, free) — for US-based applicants with SSN/ITIN
Form SS-4 by mail or fax — for foreign or special situations
By phone (international applicants): 267-941-1099

EIN application is free. Any service charging you to “get” an EIN is upcharging for free government work.

3. Individual Taxpayer Identification Number (ITIN)

A 9-digit number for individuals who must file US tax returns but can’t get an SSN. Always starts with 9.

Who needs an ITIN:

Non-resident foreigners with US tax obligations (rental income, business income)
Foreign spouses of US citizens or residents (for joint filing)
Dependents who don’t qualify for SSN
F-1 visa students with taxable scholarship income
Foreign owners of US LLCs

Who CAN’T use an ITIN:

Anyone eligible for an SSN must use the SSN instead
ITIN is not work authorization
ITIN doesn’t entitle you to Social Security benefits
ITIN is not for the Earned Income Tax Credit (EITC requires SSN)

How to get an ITIN:

File Form W-7 along with your tax return
Provide proof of identity (passport is best) and foreign status
Filed at IRS Austin Service Center or via Certified Acceptance Agent (CAA)
Processing: 7-11 weeks typically

ITIN expiration: ITINs not used on a federal return for 3 consecutive years expire and require renewal.

4. Adoption Taxpayer Identification Number (ATIN)

A temporary 9-digit number issued for children in the process of US adoption who don’t yet have an SSN.

Used for:

Claiming the child as a dependent on tax return
Claiming the Child Tax Credit
Other credits requiring child’s tax ID

How to get:

File Form W-7A
For children in domestic US adoption only
Apply when SSN can’t be obtained in time for tax filing
Replace ATIN with SSN once obtained (usually within 1-2 years of finalization)

5. Preparer Tax Identification Number (PTIN)

An 8-digit number assigned to anyone who prepares federal tax returns for pay.

Who needs a PTIN:

Paid tax preparers (CPAs, EAs, attorneys, all tax pros)
Annual Filing Season Program participants

Who doesn’t:

Volunteer preparers (VITA, TCE programs)
Family members helping each other
Self-prep (you don’t need a PTIN to do your own taxes)

How to get:

Apply online at IRS.gov/PTIN
Free for first-time applicants
Annual renewal fee: $19.75 (as of 2026)
Must be renewed each year

When you hire a paid tax preparer, verify they have a current PTIN by asking. It’s an IRS requirement and your protection against unauthorized preparers.

Filer ID / DPI (Direct Deposit Identifier)

Some states issue separate state tax IDs. Examples: California EDD employer ID, New York State EIN, Massachusetts FID. Don’t confuse with federal EIN.

Foreign Tax Identification Number (FTIN)

Tax ID issued by a foreign country (e.g., German Steuer-ID, UK National Insurance Number). Used on W-8BEN forms when claiming treaty benefits.

Centralized Authorization File (CAF) Number

Issued by IRS to tax pros for Power of Attorney (Form 2848) filings. Not a tax ID per se but a related preparer identifier.

Tax ID FAQs

Q: What’s the difference between SSN and EIN? A: SSN is for individuals; EIN is for businesses. A sole proprietor can use SSN OR get an EIN. A corporation MUST have an EIN.

Q: Can I have multiple tax IDs? A: Yes. An individual has one SSN (or ITIN). If you own a business, you have an EIN for it too. If you’re a paid tax preparer, you also have a PTIN. Three different IDs for one person is normal.

Q: Is my Social Security card the same as my tax ID card? A: For individuals: yes. Your SSN on your Social Security card is your federal tax ID. No separate “tax ID card” exists. For businesses: the IRS sends an EIN confirmation letter (CP 575) that serves as documentation, but there’s no formal card.

Q: Can my tax ID be stolen? A: Yes — tax ID theft (SSN especially) is a real threat. Symptoms: rejected return saying “already filed,” IRS notices about income you didn’t earn, unexpected wage statements. Report immediately via Form 14039 (Identity Theft Affidavit).

Q: Do I need a tax ID to open a bank account? A: Yes, in the US. Individuals: SSN or ITIN. Business accounts: EIN. Without one, you can’t open a US bank account that earns interest (banks must report to IRS).

Q: How long does it take to get an EIN? A: Online application (US applicants): immediate. Form SS-4 by fax: 4-5 business days. By mail: 4-5 weeks. Phone (foreign applicants): immediate during business hours.

Q: What if I lost my EIN? A: Look for the IRS confirmation letter (CP 575). If lost: call IRS at 800-829-4933 (Business & Specialty Tax Line). They can confirm your EIN after verification. You don’t get a new one — your EIN is for life of the business.

Q: Can a foreign person get an EIN? A: Yes. Foreign-owned LLCs and corporations need EINs. Apply via Form SS-4 (cannot use online application without SSN/ITIN). Submit by fax or call international applicant line.

What to do if you don’t know your tax ID

Lost SSN: Check old tax returns, W-2s, paystubs, Social Security card. Or request replacement card from Social Security Administration (free).

Lost EIN: Check IRS confirmation letter, prior business tax returns, business bank account documents, business filings. Call IRS at 800-829-4933 if needed.

Lost ITIN: Check prior tax returns. Or contact IRS for replacement.

Tax Calculator — Estimate federal income tax
Self-Employment Tax Calculator — For sole proprietors and 1099 income
Capital Gains Tax Calculator — For investment income

Understanding which tax ID applies to your situation is the foundation of US tax compliance. Most individuals only need an SSN; business owners need both SSN and EIN; foreign filers need ITIN; tax pros need PTIN.

1. Social Security Number (SSN)