5 TIN Types Explained: Pick the Correct Taxpayer ID [2025]

Ran into something weird last week. Client submitted paperwork with what looked like an EIN, but our system kept rejecting it. Turns out it was actually an ITIN that someone had been using incorrectly for years.

Made me realize I actually don’t know the full picture on TIN types beyond the obvious ones. Sure, everyone knows SSN and EIN, but there are three others floating around that I’ve seen pop up occasionally without really understanding when they’re supposed to be used.

Figured I’d map out all five properly since this probably isn’t the last time this’ll come up. First up, let’s cover the basics.

What is a TIN?

A Taxpayer Identification Number (TIN) is a unique identifier assigned by the Internal Revenue Service (IRS) to track individuals and entities for tax purposes in the United States. There are five different types of TINs, each designed for specific situations and legal requirements:

1. SSN (Social Security Number), for US citizens and authorized residents
2. EIN (Employer Identification Number), for businesses and entities
3. ITIN (Individual Taxpayer Identification Number), for non-residents with US tax obligations
4. PTIN (Preparer Tax Identification Number), for paid tax preparers
5. ATIN (Adoption Taxpayer Identification Number), for families in domestic adoption processes

From here, we’re going to dig deep into each one by one.

1. TIN Type for Individuals: SSN (Social Security Number)

Social Security Numbers serve dual roles as taxpayer identifiers and work authorization documents. Originally created in 1935 for retirement benefit tracking, SSNs became the backbone of US tax administration under IRC Section 6109. The nine-digit format (XXX-XX-XXXX) is issued exclusively by the Social Security Administration and stays with individuals throughout their lives.

SSN Legal Requirements

• IRC Section 6109 mandates SSNs as primary taxpayer identification numbers
• Social Security Act Section 405(c)(2)(C)(i) permits states to require SSNs for tax administration and licensing
• IRC Section 3101 requires SSN holders to pay Social Security and Medicare taxes
• The Immigration Reform and Control Act of 1986 requires SSNs for employment verification

SSN Key Use Cases

• Tax Compliance and Reporting: File individual returns, claim dependents, and report all income, including wages, self-employment earnings, and investment income, under IRC requirements.
• Employment Authorization: Conduct SSN traces to verify legal work status, process payroll taxes, and establish earnings records for Social Security and Medicare benefits
• Financial Services Access: Open bank accounts, apply for mortgages and credit cards, establish credit history, and access government-backed loan programs
• Federal Benefit Administration: Access Social Security retirement and disability benefits, Medicare enrollment, unemployment insurance, and veteran benefits
• Legal Identity Verification: Complete background checks, obtain security clearances, register to vote, and satisfy Real ID Act requirements

2. TIN Type for Businesses and Entities: EIN (Employer Identification Number)

Think of an EIN as a Social Security Number for businesses. This nine-digit identifier (XX-XXXXXXX format) separates business entities from individual taxpayers and handles everything from payroll processing to regulatory compliance. Unlike personal TINs, EINs stick with the business permanently unless major structural changes happen.

Legal Requirements

• IRC Section 6109(a)(1)(ii)(C) requires all non-individual entities to use EINs
• IRC Section 3121 mandates EINs for employers subject to FICA taxes
• Treasury Regulation 301.6109-1 requires EINs for trade or business activities
• Mandatory for filing business returns under IRC Section 6011

Key Use Cases

• Business Tax Reporting: File corporate returns (Form 1120), partnership returns (Form 1065), S-corporation elections (Form 1120S), and quarterly employment tax returns (Forms 941, 940)
• Payroll Administration: Process employee taxes, issue W-2s and 1099s, maintain employment tax compliance, and remit deposits through EFTPS
• Banking and Credit: Open business accounts, establish commercial credit lines, apply for SBA loans, and separate business finances from personal assets
• Regulatory Compliance: Apply for business licenses, register with agencies, verify other companies, comply with industry requirements, and maintain proper entity status

We’ve covered EIN comprehensively. If you are looking to read more about EIN, you can refer these guides:

• EIN Search For Business Verification: 6 Methods (Free + Paid)
• EIN Verification: Why Your Business Need it, How to Do It, and the Tools to Verify EIN
• How to Lookup a Company’s EIN Number
• EIN Verification: Frequently Asked Questions [And Quick Solutions]

3. TIN Type for Non-Residents: ITIN (Individual Taxpayer Identification Number)

ITINs fill a crucial compliance gap for people who owe US taxes but can’t get Social Security Numbers. Created for non-resident aliens, undocumented workers, and foreign individuals doing business in America, these nine-digit numbers start with “9” and follow SSN formatting (9XX-XX-XXXX). They’re purely tax tools – nothing more.

Legal Requirements

• IRC Section 6109(i) authorizes ITINs for individuals with federal tax obligations who can’t get SSNs
• Required under IRC Section 6012 for non-resident aliens with US income exceeding filing thresholds
• Mandatory for spouses and dependents claimed on tax returns per IRC Section 151
• Subject to expiration if unused for three consecutive tax years

Key Use Cases

• Individual Tax Filing: File Form 1040 series returns for US source income, including rental income, investment gains, and business profits, as required by IRC Section 6012
• Dependent Claims: Enable taxpayers to claim non-resident spouses and foreign dependents for Child Tax Credit and Credit for Other Dependents under IRC Sections 24 and 151
• Business Reporting: Report self-employment income on Schedule C, receive 1099s for contractor payments, and handle backup withholding under IRC Section 3406

4. TIN Type for Tax Professionals: PTIN (Preparer Tax Identification Number)

PTINs became mandatory in 2011 when the IRS cracked down on tax preparer oversight. If you prepare federal tax returns for money – even one return – you need one. This shift represented the IRS moving from a hands-off approach to active regulation of the tax prep industry, including background checks and competency requirements.

Legal Requirements

• IRC Section 6109(a)(4) mandates PTINs for all paid preparers since January 1, 2011
• Required regardless of volume or fee amount
• Subject to annual renewal and background checks
• Violations carry $50 penalties per return under IRC Section 6695(c)

Key Use Cases

• Professional Compliance: Sign all prepared returns with a valid PTIN as required by IRC Section 6695(b), enabling IRS tracking and disciplinary actions
• Industry Regulation: Submit to background checks, competency testing, and continuing education mandates under Circular 230
• Fraud Prevention: Enable IRS monitoring of preparation patterns and enforcement actions against fraudulent preparers

5. TIN Type for Adoption Processes: ATIN (Adoption Taxpayer Identification Number)

ATINs solve a timing problem in domestic adoptions. When families are adopting US children but can’t get the kids’ Social Security Numbers before tax season, ATINs let them claim dependents and credits without waiting. It’s a temporary fix that expires once the SSN comes through or the adoption concludes.

Legal Requirements

• IRC Section 6109 and Treasury Regulation 301.6109-3 authorize ATINs for pending domestic adoptions
• Restricted to US citizen or resident children only
• Temporary validity until SSN obtained or adoption concluded
• Required for claiming an adopted child as a dependent under IRC Section 151
• Subject to verification of legitimate adoption proceedings

Key Use Cases

• Adoption Tax Credits: Claim up to $15,950 (2024 limit) in adoption credits under IRC Section 36C for legal fees, court costs, and travel expenses during pending adoptions
• Dependent Claims: Claim child as dependent under IRC Section 151 and potentially qualify for $2,000 Child Tax Credit under IRC Section 24
• Filing Status Benefits: Qualify for Head of Household rates under IRC Section 2(b) when adoption creates a qualifying household composition
• Childcare Credits: Access Child and Dependent Care Credit under IRC Section 21 for adoption-related childcare expenses

Verifying TINs with Signzy

Here’s the problem: your business collects TINs all day – from employees, vendors, customers, whoever – but half the time you don’t know if they’re real until something breaks. You’re either calling the IRS and waiting on hold, or you’re just crossing your fingers and hoping for the best. Neither works when you’ve got deadlines.

Signzy, a verification solution serving 500+ businesses, including 10+ from Fortune 30, fixes this in three ways:

🎯 Instant Validation: Check TIN authenticity against IRS databases in real-time, so you know immediately if a number is valid instead of finding out weeks later when returns get rejected.

🎯 All Five TIN Types: One system handles SSNs, EINs, ITINs, PTINs, and ATINs without needing separate integrations for each type – because your customers use all of them.

🎯 Compliance Built-In: Automated audit trails, privacy law compliance, and regulatory checks happen behind the scenes, so you focus on business instead of paperwork.

Long story short, TIN verification shouldn’t be your full-time job. Let us handle it so you can get back to whatever actually makes you money. To know more about how Signzy can help, book a demo here.