What Do the Eight Digits of an Insurer Number Tell You? — Law-Type Numbers, Prefecture Numbers and Check Digits Read from a Receipt Computer's Implementation (archived 2026-08-30)

Abstract

The insurer number on a Japanese health insurance card is made up of a 2-digit law-type number, a 2-digit prefecture number, a 3-digit per-insurer number and a 1-digit check digit. Taking the Ministry of Health, Labour and Welfare's setting guidelines as the primary source, this article takes the structure apart and verifies the check digit calculation and ORCA's (Nichi-Rece's) COBOL implementation against the published source. Archived version of https://comcomponent.com/en/blog/insurer-number-structure/, as published on 2026-08-30. The live article is maintained and may change after this date. First published 2026-07-18.