How is an NPI check digit calculated?

With the Luhn algorithm over the prefix 80840 followed by the first nine digits of the NPI. The tenth digit must equal the result.

Is NPPES data public?

Yes. CMS publishes NPPES as FOIA-disclosable data, free to download and redistribute.

NPI API

Validate NPI numbers and look up US providers from the CMS NPPES registry: names, addresses and taxonomy codes. Provider endpoints are coming soon; validation is live.

Source: CMS NPPES
Updated: Weekly
License: Public (FOIA-disclosable)
Live version: Coming soon

Request (planned)

GET /v1/providers/1234567893/validate

Response (planned)

{
  "data": {
    "npi": "1234567893",
    "valid_check_digit": true
  },
  "meta": {
    "source": "nppes"
  }
}

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# Provider endpoints are coming soon. Check digit today:
npx @healthcare.dev/cli npi 1234567893

About the data

NPI registry (NPPES)

Every US health care provider who bills electronically has a 10-digit National Provider Identifier. CMS publishes the full NPPES registry weekly: names, practice addresses, taxonomy codes and deactivations.

Provider search and lookup endpoints are being built on the full NPPES file. Today the free NPI lookup checks the check digit and queries the public NPPES registry, and the MCP tool validate_npi and the SDK helper isValidNpi check format and check digit.

Source: CMS NPPES. Full field reference in the docs.

Endpoint: /v1/providers/{npi}
Source id: nppes
Cadence: Weekly
License: Public (FOIA-disclosable)

Questions

NPI API FAQ

How is an NPI check digit calculated?: With the Luhn algorithm over the prefix 80840 followed by the first nine digits of the NPI. The tenth digit must equal the result.
Is NPPES data public?: Yes. CMS publishes NPPES as FOIA-disclosable data, free to download and redistribute.