Generator · Belgian data
Belgian Rijksregisternummer
Endpoint GET /v1/be/rijksregisternummer
What it covers
Returns a valid Belgian Rijksregisternummer (RRN) with correct check digits. Constrain with `sex` and age/birth-date filters (the full birth date is encoded). Use `kind=bis` for a BIS-number. Contradictory combinations are rejected with a 400. Set `invalid=true` for deliberately wrong check digits.
The two-digit year cannot distinguish 1900s from 2000s births, so the checksum itself carries the century marker: for births in 2000 or later, a literal digit '2' is prepended to the nine-digit payload before the modulo is taken (i.e. `97 − ((2 followed by first9) mod 97)`). Validators must try both bases when the century is unknown.
How it’s calculated
The two RRN check digits are the mod-97 complement of the nine payload digits — `97 − (first9 mod 97)` — with a literal '2' prepended to the payload for births in the year 2000 or later to disambiguate the century.
Algorithm
- Take the first nine digits of the RRN (the payload): a 6-digit YYMMDD date head followed by a 3-digit serial. This is the string called `firstNine`.
- Determine the birth year. If the birth year is 2000 or later, prepend the single digit '2' to the front of the nine-digit payload, forming a 10-character basis string. If the birth year is 1999 or earlier, use the nine-digit payload unchanged as the basis.
- Interpret the basis string as one large integer and compute its remainder modulo 97 (mod97 uses BigInt: `Number(BigInt(basis) % 97n)`).
- Compute the two check digits as `97 - (basis mod 97)`.
- Zero-pad the result to exactly two digits (e.g. 7 -> '07').
- Append these two check digits to the nine payload digits to form the full 11-digit RRN.
Worked example
RRN for a male born 1990-05-23, serial 001: 900523001??
Payload (first nine digits) = 900523001 (YY=90, MM=05, DD=23, serial=001).
Birth year 1990 is before 2000, so no '2' prefix — basis = 900523001.
900523001 mod 97 = 27.
Check = 97 − 27 = 70.
Zero-pad to two digits: '70' (already two digits).
Full RRN = 900523001 followed by 70 = 90052300170.The check digits are 70, giving the full RRN 90052300170.
Edge cases
- The month field of the date head carries a BIS offset for non-national numbers: +40 when the sex is known, +20 when it is not; the actual month/day/year are never altered, so the birth date is recoverable by subtracting the offset before checksum validation still applies to the offset digits as written.
- The serial (digits 7-9) is clamped to 001..998; the registry never issues serial 000 or 999.
- Serial parity encodes sex: odd serial = male, even serial = female.
Gotchas
- The check is a plain complement (97 minus the remainder), NOT the ISO 7064 MOD 97-10 IBAN-style scheme. Do not use `98 - (payload*100 mod 97)` — this generator calls the plain `mod97()` and subtracts from 97.
- The '2' prefix for years ≥ 2000 is a literal string concatenation on the front of the nine digits before the BigInt conversion, changing the modulo result — it is not an arithmetic add of 2,000,000,000 done separately (though the source comment describes it that way, the code does string prepend).
- A remainder of 0 yields check digits '97', which is a valid RRN check value.
Parameters
| Parameter | Type | Description |
|---|---|---|
| atAge | integer | Exact age in years at request time. |
| bornAfter | stringpattern ^\d{4}(?:-\d{2}(?:-\d{2})?)?$ | Born after this date or fragment (YYYY, YYYY-MM, YYYY-MM-DD). |
| bornBefore | stringpattern ^\d{4}(?:-\d{2}(?:-\d{2})?)?$ | Born before this date or fragment (YYYY, YYYY-MM, YYYY-MM-DD). |
| bornOn | stringpattern ^\d{4}(?:-\d{2}(?:-\d{2})?)?$ | Born on a date or within a fragment: YYYY, YYYY-MM, or YYYY-MM-DD. |
| count | integer1–1000 | Number of records to return, 1–1000 (your plan may lower this). Omitted returns a single record; set it for a batch. |
| edge | boolean | Restrict output to edge-case values. |
| extreme | boolean | Return a correct value wrapped in a hostile encoding (untrimmed whitespace, invisible/zero-width characters, BOM, or bidi/combining marks). Homoglyphs are excluded so the value stays machine-parseable; it still validates after normalisation. |
| invalid | boolean | Return an RRN with deliberately wrong check digits; birth date/sex stay valid. |
| kind | "national" | "bis" | Number kind: ordinary national RRN (default) or a BIS-number. |
| olderThan | integer | Minimum age in years at request time. |
| seed | integer | Integer seed for reproducible output: the same seed always yields the same record. |
| sex | "m" | "f" | Encoded sex: "m" or "f". |
| youngerThan | integer | Maximum age in years at request time. |
Response fields
| Field | Type | Description |
|---|---|---|
| value | string | The 11-digit RRN rendered as bare digits. |
| digits | string | The canonical 11-digit RRN. |
| birthDate | string | The encoded birth date, ISO `YYYY-MM-DD`. |
| sex | "m" | "f" | Encoded sex: `m` (odd serial) or `f` (even serial). |
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