What does a Belgian national number contain?

It is 11 digits: YYMMDD for the date of birth, a 3-digit sequence number (odd = male, even = female), and a 2-digit modulo-97 check number.

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 (the first nine digits plus 2,000,000,000) before taking modulo 97. The decoder tries both and uses whichever matches to fix the century.

How is the gender determined?

From the 3-digit sequence number: an odd value means male, an even value means female. This is fixed by the structure of the number.

What is a bis-number?

A bis-number is issued to people without a standard national registration. The month is encoded as the real month plus 20 (gender unknown at registration) or plus 40 (gender known). The decoder detects this and restores the true month.

Does a valid checksum mean the number is real?

No. A matching modulo-97 check only proves the number is internally consistent. It does not prove it was actually issued to a real person — only the National Register can confirm that.

Why does my number show "century undetermined"?

If the provided check digits match neither the 1900s nor the 2000s formula, the decoder cannot pick a century and flags the checksum as invalid — usually a sign of a typo.

Is my national number sent anywhere?

No. 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 (NRN). The tool reads the date of birth, the gender and the birth century, and validates the number with its built-in checksum. It is useful for HR, onboarding and data-entry checks where you need to interpret or sanity-check a national number.

How it works

The number splits as YYMMDD SSS CC. The first six digits are the date of birth, the next three are a sequence number whose parity gives gender (odd = male, even = female), and the last two are a modulo-97 check. To find the century, the tool computes two candidate checks from the first nine digits N:

pre-2000: 97 − (N mod 97) 2000+: 97 − ((2,000,000,000 + N) mod 97)

Whichever matches the printed check digits fixes the century. Bis-numbers, where the month is stored as month + 20 or + 40, are detected and the real month is restored.

Example

For 85073003328:

Field	Value
Date of birth	30 July 1985
Gender	Male (sequence 033 is odd)
Sequence	033
Modulo-97 check	Valid (matches the pre-2000 formula)

All processing happens locally in your browser — the decoder never contacts the National Register and nothing is uploaded.