NPI check digit
The prefix 80840 is the card issuer identifier CMS uses for the check. It is not part of the 10 digits you type.
Source: CMS, National Provider Identifier Standard, check-digit description. Page read October 14, 2026.
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Definition · Provider identifiers and enrollment
NPI check digit
The tenth digit of an NPI is a check digit. CMS computes it with the Luhn formula, after prefixing the nine-digit identifier with 80840. A failed check means the number was typed wrong. It does not mean the NPI is deactivated or excluded. The lookup is at /npi-lookup.
Questions
NPI check digit, answered
Does a valid check digit mean the NPI is active?
No. It only means the digits fit the formula. Active status comes from the NPPES record.