This Belgian rijksregisternummer validator checks the official mod-97
checksum used by Belgium's national register number, automatically handling both the
pre-2000 and post-2000 birth-year formulas. Everything runs in your browser.
How to use it
Paste the 11-digit number with or without the usual dots and dashes (e.g.
85.07.30-033.28 or 85073003328) and click "Check number". The
tool strips formatting automatically before validating.
How the mod-97 checksum works
The first 9 digits (birth date + sequence number) are treated as one large number. For
births before 2000, the check digits equal 97 − (number mod 97). For births in
2000 or later, the digit "2" is prepended to that 9-digit number before the same formula, to
avoid collisions with 20th-century numbers. This tool computes both and accepts a match on
either.
Structure of the number
Positions 1–6 encode the birth date (YYMMDD), positions 7–9 are a sequence number
(odd for men, even for women, historically), and the final two digits are the checksum.
Special encodings exist for unknown birth dates and for BIS numbers issued to people not
born in Belgium — this tool focuses on the checksum rather than rejecting those edge cases.
Frequently asked questions
What is a rijksregisternummer?
The rijksregisternummer (or "numéro de registre national" in French, "national number" / "INSZ" for BIS numbers) is Belgium's 11-digit national identification number, encoding a person's birth date, a sequence number, and a 2-digit checksum.
Why does the tool check two different formulas?
The checksum is computed differently depending on birth century: for people born before 2000, it's 97 minus the first 9 digits modulo 97; for people born in 2000 or later, "2" is prepended to those 9 digits before the same calculation, because the number space wrapped around. Since a bare number doesn't say which century, this tool accepts it as valid if it matches either formula.
What do the first 6 digits mean?
They're the birth date as YYMMDD. Belgium also uses documented special values here — for example DD = 00 when the exact day of birth is unknown, and offsets on the month for certain BIS numbers issued to foreign nationals — so this tool doesn't reject numbers just for having an unusual date segment.
Is my rijksregisternummer sent anywhere?
No. The checksum is computed entirely in your browser via JavaScript — nothing is transmitted, logged, or stored. That matters, since this number is one of the most sensitive personal identifiers in Belgium.
Does a valid checksum mean the number is real?
No — same caveat as any checksum-based validator. It confirms the number is structurally well-formed and free of common typos, not that it was actually issued to a real person. There is no public Belgian government API to confirm that.