taxpayer identification number (TIN)

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A taxpayer identification number (TIN) is a unique nine-digit number assigned to a person or entity. The Internal Revenue Service (IRS) uses TINs for tax purposes to identify and track taxpayers. Among others, TINs are mandatory to file tax returns or claim treaty benefits.

The following are the types of TINs:

  • Social Security Number (SSN).
  • Employer Identification Number (EIN).
  • Individual Taxpayer Identification Number (ITIN).
  • Taxpayer Identification Number for Pending U.S. Adoptions (ATIN).
  • Preparer Taxpayer Identification Number (PTIN).

TINs can be issued by the Social Security Administration (SSA) or by the IRS. The SSA issues the SSN, whereas the IRS issues all other TINs listed above.

[Last updated in October of 2021 by the Wex Definitions Team]