How does the modulo-97 checksum determine the century?

For births before 2000 the check equals 97 minus the first nine digits modulo 97. For births from 2000 a leading 2 is prepended before taking modulo 97. The decoder tries both and uses whichever matches to fix the century.

How accurate is the gender reading?

Gender comes from the three-digit sequence number — odd means male, even means female. This is deterministic from the structure, but a valid checksum does not prove the number was actually issued to a real person.

Is my national number sent anywhere?

No. The decoder is privacy-first — all processing happens locally in your browser and the number never leaves your device.

Belgium National Number Decoder

Belgium national number decoder

Decode an 11-digit Belgian Rijksregisternummer / Numéro de Registre National. The tool reads the date of birth, the gender (from the parity of the sequence number) and the birth century, which it determines by testing the modulo-97 checksum against both the pre-2000 and post-2000 formulas. It also detects bis-numbers (month + 20 or + 40).

It is privacy-first: nothing leaves your browser. The decoder only interprets the structure and checksum — it does not check it against the National Register.