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NPI

General

National Provider Identifier

A 10-digit identification number issued by CMS to US healthcare providers, used on claims, referrals, and billing across the entire healthcare system.

Definition

A National Provider Identifier (NPI) is a 10-digit number issued by the Centers for Medicare & Medicaid Services (CMS) to identify individual healthcare providers and healthcare organizations across the United States. Mandated under HIPAA, the NPI is used on virtually every healthcare transaction — claims, referrals, prescriptions, and billing — replacing the patchwork of separate provider IDs that different insurers previously required.

There are two types: Type 1 for individual providers (physicians, therapists, nurse practitioners) and Type 2 for organizations (hospitals, clinics, group practices). Both share the identical 10-digit format.

Formula

An NPI's check digit is computed using the Luhn algorithm — the same checksum used for credit card numbers — but with a twist: the fixed 5-digit prefix 80840 (the ISO 7812 issuer identifier reserved for US healthcare) is prepended to the 9-digit provider number before running the Luhn calculation. The steps are:

  1. Prepend 80840 to the first 9 digits of the NPI, forming a 14-digit string.
  2. Apply the standard Luhn algorithm: starting from the rightmost digit, double every second digit, subtracting 9 from any result over 9.
  3. Sum all digits; the 10th digit of the NPI must make the total sum a multiple of 10.

This makes NPIs checksum-verifiable offline, unlike identifiers such as a DUNS Number that rely purely on registry lookup.

Worked Example

A structurally valid example that passes the Luhn checksum: 1234567893.

Key Things to Know

  • 10 digits, Luhn-checksummed: the final digit is mathematically derived from the first 9 plus a fixed prefix, so most typos are caught instantly by the NPI Validator.
  • Type 1 vs. Type 2: individual providers get Type 1 NPIs; organizations get Type 2 — both use the same format.
  • Permanent and portable: an NPI never changes, even across job or state changes, unlike state medical license numbers.
  • Distinct from Medicare ID: an NPI identifies the provider; a Medicare ID identifies the patient — claims reference both.
  • Free and mandatory under HIPAA: registration through NPPES is free, and use of the NPI is legally required on standard healthcare transactions.
  • Related to EIN for organizations: Type 2 organizational NPIs are typically linked to the organization's EIN during registration for tax and billing reconciliation.

Related Terms

Medicare IDMedicare Beneficiary Identifier (MBI)EINUS Employer Identification Number

Frequently Asked Questions

An NPI's 10th digit is a Luhn checksum computed from the first 9 digits after prefixing them with a fixed constant (80840, the ISO health-industry identifier prefix) — the same Luhn algorithm used for credit card numbers. You can check whether a number passes this checksum with the [NPI Validator](/validators/npi-validator/).
A Type 1 NPI identifies an individual healthcare provider, such as a physician or nurse practitioner, while a Type 2 NPI identifies an organizational healthcare entity, such as a hospital, clinic, or group practice. Both types share the same 10-digit format and Luhn checksum rule — the distinction is administrative, not structural.
No. An NPI identifies the healthcare provider or organization delivering care, while a [Medicare ID](/glossary/medicare-id/) (MBI) identifies the patient receiving Medicare benefits. A single medical claim typically references both numbers — one for who provided the service, one for who received it.
NPIs are assigned by the National Plan and Provider Enumeration System (NPPES), which is operated by the Centers for Medicare & Medicaid Services (CMS). Registration is free, and the assigned number is permanent — it does not change even if a provider changes practices, states, or specialties.
The Luhn checksum for NPIs is computed by prepending the fixed prefix 80840 to the 9-digit provider identifier before applying the standard Luhn algorithm — this prefix is the ISO 7812 issuer identifier reserved for the US health industry, not part of the visible NPI itself. It ensures NPIs are checksum-compatible with other Luhn-validated numbering systems used internationally in healthcare.