NPI Validator

How it is calculated

A US National Provider Identifier has 10 digits: 9 identifying digits and a final check digit. The tool strips non-digits, requires exactly 10 digits, and applies the Luhn algorithm to the string 80840 followed by the first 9 digits. The prefix 80840 is part of the standard NPI check, so the check digit it produces is the same one that a payer's system expects.

Starting from the rightmost digit of that 14-digit string, every second digit is doubled (subtracting 9 if the result exceeds 9) and all are added. The expected check digit is (10 − sum mod 10) mod 10. If it equals the tenth digit you entered, the number is valid. This confirms only the structure; it does not prove that the number is assigned to a real provider.

Common mistakes

• Entering a number that is not 10 digits long, such as an NPI with a typo or an extra digit; the tool then returns no result.
• Treating a valid result as proof that the provider exists or is active. Registry lookup is the only way to confirm that.
• Confusing the NPI with a DEA number, tax ID or licence number, which follow different rules.
• Running a plain Luhn check without the 80840 prefix, which gives the wrong check digit.