NPI number validator
Type an NPI to see if its check digit is correct — a quick way to catch typos before a claim is rejected.
How the NPI check digit works
An NPI has nine identifier digits and a tenth check digit. The check digit uses the Luhn formula (ISO/IEC 7812) applied as if the number started with the health-industry prefix 80840:
- Take the first nine digits, and starting from the rightmost one, double every other digit.
- If doubling gives a two-digit number, add its digits (or subtract 9).
- Add up all nine resulting digits, plus 24 — the constant contributed by the 80840 prefix.
- The check digit is the amount needed to reach the next multiple of 10.
Example: for 123456789 the doubled positions give 2, 6, 10→1, 14→5, 18→9 and the others are 2, 4, 6, 8; the total is 43 + 24 = 67, so the check digit is 3 and the full NPI is 1234567893.
A valid check digit only means the number is well-formed. To see whether it was issued and is active, look it up or use thebulk checker.