Definition
Taxpayer Identification Number (TIN)
A Taxpayer Identification Number (TIN) is the number the Internal Revenue Service uses to identify a taxpayer. In healthcare it identifies the business entity paid for claims, usually an Employer Identification Number (EIN) or, for some sole proprietors, a Social Security Number.
2 min readReviewed September 14, 2026
Also known as: Tax ID, Employer Identification Number, EIN, Federal tax ID number
Key facts
- Issued by
- IRS (EIN, ITIN) or Social Security Administration (SSN)
- Common types
- Employer Identification Number, Social Security Number, ITIN
- EIN format
- 9 digits, written XX-XXXXXXX
- Role in healthcare
- Identifies the entity that is paid; one TIN can cover many NPIs
What is a Taxpayer Identification Number?
TIN is an umbrella term for several federal tax identifiers. Businesses, including medical groups, hospitals and pharmacies, use an Employer Identification Number (EIN). Individuals use a Social Security Number, or an Individual Taxpayer Identification Number (ITIN) if they are not eligible for one.
Health plans need a provider's TIN to pay claims and to report those payments to the IRS. Providers typically supply it on IRS Form W-9 during contracting and enrollment.
How TINs and NPIs fit together
The National Provider Identifier (NPI) identifies who provided care, while the TIN identifies who gets paid:
- A solo clinician billing as a sole proprietor uses one Type 1 NPI with a Social Security Number or an EIN.
- A group practice has one TIN, usually at least one Type 2 NPI, and a Type 1 NPI for every clinician.
- A clinician who works for two groups bills under two different TINs with the same individual NPI.
- A health system may use separate TINs for its hospitals, physician groups and other entities.
Why the TIN matters
Payers contract, pay and measure at the TIN level. The Merit-based Incentive Payment System (MIPS) evaluates clinicians by TIN and NPI combination or as a group under a TIN, and accountable care organizations in the Medicare Shared Savings Program are built from participant TINs.
Under the federal Transparency in Coverage rule, health plans publish in-network rate files that identify providers by NPI and TIN. That makes the TIN the key for grouping negotiated rates by practice or health system and for studying consolidation.
Limitations of TIN data
TINs are not included in public NPPES files, and a Social Security Number used as a TIN is never published. Mapping clinicians to the entities that bill for them therefore often relies on price transparency files, or on Medicare data that links clinicians to groups through other identifiers without publishing the TIN itself.