NPI number validator
Check whether a 10-digit number is a correctly formed NPI. The test runs in your browser and nothing is sent to any server.
Enter an NPI to check its format and check digit.
How the check digit works
An NPI’s tenth digit is a Luhn check digit calculated over the constant 80840 plus the first nine digits. Doubling alternate digits, adding them up, adding 24 for the 80840 prefix, and rounding up to the next multiple of 10 gives the check digit.
Worked example for the first nine digits 123456789:
- Starting from the rightmost digit, double every other digit: 9→18, 7→14, 5→10, 3→6, 1→2. Digits that were not doubled stay as they are.
- Add the individual digits: 1+8 + 8 + 1+4 + 6 + 1+0 + 4 + 6 + 2 + 2 = 43.
- Add 24 for the 80840 prefix: 43 + 24 = 67.
- The next multiple of 10 is 70, so the check digit is 70 − 67 = 3, giving NPI 1234567893.
Frequently asked questions
Does a valid check digit mean the NPI exists?
No. Roughly one in ten random 10-digit numbers passes the check, so a pass only means the number is well formed. Use NPI lookup to see whether the registry has it.
What is the check digit?
The tenth digit of an NPI. It is calculated from the first nine digits with the Luhn algorithm, using the constant 80840 as a prefix, so typing mistakes are caught.