Ontario health card number validator.

How the Ontario health card number check digit is calculated

An Ontario health card number (the number OHIP claims are billed against) is 10 digits, printed 1234-567-890. The Ministry of Health tells billing systems to verify it with its MOD 10 check digit routine before submitting a claim, to cut rejected claims.

1. Take the first 9 digits and double the 1st, 3rd, 5th, 7th and 9th. If a product is 10 or more, add its two digits (so 18 becomes 1 + 8 = 9).
2. Add those results to the untouched 2nd, 4th, 6th and 8th digits.
3. Subtract the units digit of the total from 10 (a units digit of 0 gives 0). The answer must equal the 10th digit.

Worked example (from the Ministry spec): 987654321 → 9, 8, 5 (7 doubled is 14, 1 + 4), 6, 1 (5 doubled is 10, 1 + 0), 4, 6, 2, 2, which total 43. The units digit is 3, and 10 − 3 = 7, so 9876543217 is valid. This is the same as a standard Luhn check over all 10 digits.

The version code

The one or two letters after the number are the card's version code, which changes when a new card is issued for the same number. Per the spec it is 1 or 2 letters, required on health-card claims, and it is not part of the checksum. This tool accepts it and shows it, but cannot tell whether it is the current version.

Sources

• Ontario Ministry of Health, Interface to Health Care Systems Technical Specifications v6.2, s4.14 (Markdown mirror: carlos-emr/carlos).
• Agreeing implementations: openmed clinical_ids.py and med_simple HealthCardValidator.