1.2 Taxpayer Identification Numbers & Identity Protection

Statutory Overview of Identifying Numbers (IRC §6109)

Under IRC §6109, every person required to make a return, statement, or other document with the Internal Revenue Service must supply a Taxpayer Identification Number (TIN). For individuals, this identification serves as the primary index key linking wage statements, information returns, bank reporting, and tax liabilities in the IRS Information Returns Program (IRP).

There are five discrete classes of identification numbers within federal tax administration:

1. Social Security Number (SSN)
2. Individual Taxpayer Identification Number (ITIN)
3. Adoption Taxpayer Identification Number (ATIN)
4. Employer Identification Number (EIN)
5. Preparer Tax Identification Number (PTIN)

Social Security Numbers (SSN)

An SSN is a nine-digit number in the format 000-00-0000, administered and issued solely by the Social Security Administration (SSA) via Form SS-5 (Application for a Social Security Card). It is available only to:

• U.S. citizens;
• Lawfully admitted permanent residents (Green Card holders); and
• Noncitizens who have received Department of Homeland Security (DHS) authorization to work in the United States.

Crucial Credit Restrictions Tied to SSNs

On the Special Enrollment Examination, the legal distinction between an SSN and an ITIN is tested extensively regarding tax credit eligibility:

• Child Tax Credit (CTC / IRC §24(h)(7)): Under the Code, no Child Tax Credit or refundable Additional Child Tax Credit (ACTC) is allowable for a qualifying child unless the child possesses an SSN that was issued on or before the due date of the tax return (including valid extensions). The SSN must be valid for employment in the United States. An ITIN or ATIN child does not qualify for the Child Tax Credit. Beginning with 2025 returns, the One Big Beautiful Bill Act (OBBBA) also requires the taxpayer to have a work-eligible SSN (on a joint return, at least one spouse), and it raised the credit to $2,200 per qualifying child, of which up to $1,700 is refundable as the ACTC.
• Earned Income Tax Credit (EITC / IRC §32(m)): To claim the EITC, the taxpayer, the taxpayer's spouse (if filing jointly), and any qualifying child must each possess an SSN valid for employment issued on or before the due date of the return (including extensions). An individual filing with an ITIN cannot claim the EITC under any circumstance.

Individual Taxpayer Identification Numbers (ITIN)

An ITIN is a nine-digit number issued by the IRS to foreign nationals and other individuals who are required to have a U.S. taxpayer identification number for federal tax reporting, but who are not eligible to obtain an SSN from the SSA. ITINs are formatted like SSNs (9XX-XX-XXXX), always begin with the number 9, and feature specific middle two digits (historically 50–65, 70–88, 90–92, and 94–99).

Application Procedures (Form W-7)

An ITIN is requested using Form W-7 (Application for IRS Individual Taxpayer Identification Number). Key procedural requirements include:

• Attachment to Tax Return: Form W-7 must generally be attached to the front of a complete, original federal income tax return (Form 1040 or Form 1040-NR) for which the ITIN is required, unless a statutory exception applies (e.g., individuals claiming treaty benefits, third-party withholding, or partnership passive investments).
• Identity & Foreign Status Documentation: Applicants must provide original documentation, or certified copies directly from the original issuing government agency. A valid, unexpired foreign passport is the only stand-alone document that establishes both identity and foreign status. If a passport is not submitted, the applicant must submit a combination of at least two other current documents (such as a national identity card, foreign birth certificate, or foreign voter registration card), at least one of which must include a photograph.
• Submission Methods: Form W-7 packages may be submitted by mail to the IRS ITIN Operation in Austin, Texas, presented in person at an IRS Taxpayer Assistance Center (TAC), or submitted through an IRS-authorized Certified Acceptance Agent (CAA), who is permitted to verify and certify original identity documents on behalf of applicants.

Scope and Inherent Limitations

• Tax Administration Only: An ITIN is issued strictly for federal tax administration. It does not confer legal immigration status, does not grant work authorization, and does not establish eligibility for Social Security retirement or disability benefits.
• Credit for Other Dependents (ODC): While an ITIN child is statutorily disqualified from the $2,200 (2025) Child Tax Credit, a dependent with an ITIN who meets the dependent relationship, age, and residency requirements qualifies for the nonrefundable $500 Credit for Other Dependents (ODC).

ITIN Expiration and Renewal Rules

Under IRC §6109(i), ITINs expire under two distinct mechanisms:

1. Three-Year Non-Use Rule: If an ITIN is not used on a federal income tax return (including as a dependent or spouse) for three consecutive tax years, it expires. The IRS applies the rule at the end of the calendar year in which the third unused return would have been filed: an ITIN not included on a federal tax return for tax years 2022, 2023, and 2024 expired on December 31, 2025.
2. Legacy Middle-Digit Schedule: ITINs issued before 2013 expired on a phased schedule keyed to their middle digits; that schedule has run its course, so the non-use rule now drives expirations. A taxpayer renews an expired ITIN by filing Form W-7 (checking the renewal box) with the required documents; the original ITIN is reactivated rather than replaced.

Adoption Taxpayer Identification Numbers (ATIN)

An ATIN is a temporary nine-digit identification number issued by the IRS via Form W-7A (Application for Taxpayer Identification Number for Pending U.S. Adoptions). It is designed for domestic children placed in a home for legal adoption when the adoptive parents are unable to obtain the child's SSN in time to file their tax return.

• Domestic Placements: An ATIN is intended for domestic adoptions. A child adopted from abroad qualifies only after being admitted to the United States with a green card or certificate of citizenship; otherwise the parents must seek an ITIN (or, once available, an SSN).
• Expiration: An ATIN automatically expires two years after the date of issuance. If the adoption is not finalized within two years, the adoptive parents must file a written extension request before expiration.
• Credit Utilization: An ATIN lets the parents claim the child as a dependent, use the child for head of household status and the child and dependent care credit, and claim the $500 Credit for Other Dependents while the adoption is pending. It does not support the Child Tax Credit, which requires the child's SSN issued by the return due date. Once the SSN arrives, the parents stop using the ATIN.

Preparer Tax Identification Numbers (PTIN)

Under IRC §6109(a)(4) and Treas. Reg. §1.6109-2, any individual who prepares or assists in preparing all or substantially all of a federal tax return or claim for refund for compensation must have a valid Preparer Tax Identification Number (PTIN). The PTIN must be entered on the paid preparer section of every return filed.

• Format: A nine-character alphanumeric string beginning with the letter "P" followed by eight digits (P00000000).
• Annual Renewal: PTINs are valid for a single calendar year and must be renewed annually, typically between mid-October and December 31 for the upcoming filing season.
• Enrolled Agent Rule: All Enrolled Agents must maintain an active PTIN to represent taxpayers before the IRS and prepare returns, regardless of whether they prepare returns full-time or part-time.

Identity Protection PIN (IP PIN) & Identity Theft Procedures

The IRS Identity Protection Personal Identification Number (IP PIN) is a six-digit number assigned to prevent the fraudulent use of a taxpayer's SSN or ITIN on federal income tax returns.

• Notice CP01A: Confirmed identity theft victims are automatically placed in the IP PIN program and receive IRS Notice CP01A annually in December or early January containing their new IP PIN.
• Annual Reissuance: A new IP PIN is generated every calendar year. An IP PIN issued for 2025 cannot be used on a return filed in 2026.
• Mandatory Electronic Filing Requirement: Once an IP PIN is assigned to a primary taxpayer, spouse, or dependent, that exact six-digit code must be entered on any electronic return. If the IP PIN is missing or incorrect, IRS e-file systems reject the return. If a paper return is filed without the correct IP PIN, it is routed for additional identity screening, causing substantial processing delays.
• Voluntary Program: Any taxpayer with an SSN or ITIN can voluntarily opt into the IP PIN program via their secure IRS online account to protect their account against fraudulent returns.
• Form 14039 (Identity Theft Affidavit): When a taxpayer discovers their identity has been stolen—most commonly when an e-filed return is rejected because a return has already been filed using their SSN—they file Form 14039, either online or attached to the paper Form 1040 they must then file, so the IRS can open an identity theft case and sort out the legitimate return.

Missing or Mismatched TINs: Math Error Authority (IRC §6213(g))

Under IRC §6213(g)(2), the omission or mismatch of an SSN, ITIN, or ATIN is statutorily classified as a mathematical or clerical error.

• Summary Assessment: When a TIN error occurs (such as an incorrect birth date, transposed digits, or an ITIN entered for the Child Tax Credit), the IRS has statutory authority to summarily assess additional tax and disallow the credit or dependency exemption immediately, without issuing a formal 90-day Statutory Notice of Deficiency.
• 60-Day Abatement Window: Upon receiving an IRS math error notice (e.g., Notice CP11 or CP12), the taxpayer has 60 days from the date of the notice to request an abatement of the assessment. If the taxpayer files a timely written request, the IRS must abate the assessment and follow standard deficiency procedures, restoring the taxpayer's prepayment appeal rights to the U.S. Tax Court.

Summary Matrix of Taxpayer Identification Numbers