Function: npiCheckDigit()

npiCheckDigit(base9): number

The correct NPI check digit for a 9-digit base - the value that makes 80840 + base + check pass the Luhn check.

Parameters

base9

string

The 9-digit NPI base (positions 1–9).

Returns

number

The check digit (0–9) a real NPI would carry for this base.

Example

import { npiCheckDigit } from "@cosyte/synth";
npiCheckDigit("123456789"); // 3 - so 1234567893 is a Luhn-valid NPI shape