Free tool
NPI validator
Check whether a 10-digit National Provider Identifier is structurally valid. Useful for catching typos in claims, rosters, and credentialing files before they bounce.
Validating a whole list? Try the bulk validator.
Type or paste a 10-digit NPI. The check runs instantly in your browser; nothing is sent to a server.
How the NPI checksum works
Every NPI carries its own error check. The tenth digit is a check digit computed from the first nine using the Luhn algorithm, the same scheme used on payment card numbers, as specified by CMS:
- Prefix the first 9 digits with 80840, the ISO 7812 issuer prefix for US health providers (80 identifies health applications, 840 is the country code for the United States).
- Starting from the rightmost digit of that 14-digit string, double every second digit. When a double exceeds 9, subtract 9.
- Sum all resulting digits.
- The check digit is whatever brings the sum up to the next multiple of 10. If it matches the NPI's tenth digit, the number is structurally valid.
A passing checksum means the number is well-formed, not that it is registered. To confirm a real assignment, use our NPI lookup or the CMS NPI registry.