What this checker does
Paste a Belgian rijksregisternummer (Dutch), numéro de registre national (French) or BIS number and the page tells you immediately whether the structure and the two check digits are correct. If the number is valid it also reads the birth date and the sex that are encoded in it. Spaces, dots and dashes are ignored, so you can paste 85.07.30-033.28, 85073003328 or a number copied from a PDF without cleaning it first.
The check happens in your browser. The number is never sent to a server and never stored, which matters because a national number is personal data. If you need to scan a whole text or spreadsheet for several kinds of Belgian identifier at once, use the Belgian Identifier Detector.
How the number is built
An 11-digit national number has the shape YY.MM.DD-SSS.CC:
- YY.MM.DD – the birth date: year (two digits), month and day.
- SSS – a three-digit sequence number for people born on the same day. It is odd for men and even for women.
- CC – two check digits that protect the first nine digits against typing errors.
The check digits are 97 − (first nine digits mod 97). For anyone born in 2000 or later, a 2 is put in front of the nine digits before the calculation. This is how a checker can tell a person born in 1917 from one born in 2017 even though the printed year is the same.
Worked examples
Born before 2000. Take 85.07.30-033.28, a commonly used example. The first nine digits are 850730033. Dividing by 97 leaves a remainder of 69, and 97 − 69 = 28, which matches the last two digits. The sequence number 033 is odd, so the number encodes a man born on 30 July 1985.
Born in 2000 or later. Take 99.01.01-001.47. Calculated as a 1999 birth it fails. Calculated with the leading 2, the number 2990101001 leaves a remainder of 50 and 97 − 50 = 47, so it is valid only as a birth date of 1 January 2099. That is also why the test-number generator uses a date in 2099 by default: the result cannot belong to a real person.
BIS numbers and partly unknown dates
People who are not in the national register, such as many foreign workers, receive a BIS number from the Crossroads Bank for Social Security. A BIS number looks like a national number but the month is shifted: +20 when the sex was not known at registration and +40 when it was known. A month or day of 00 means the birth date is only partly known. The checker recognises these variants and explains which one it found.
Together, national numbers and BIS numbers are called INSZ in Dutch and NISS in French (identification number of social security). If a form asks for an INSZ or NISS, either type is accepted.
Common reasons a number is rejected
- A digit was mistyped or two digits were swapped – the check digits no longer match.
- The number was copied with a leading or trailing digit that is not part of it, for example a page or line number.
- The month is 13 or higher without being a BIS offset, or the day does not exist in that month.
- The number belongs to a different system, such as an enterprise number. For companies use the VAT and KBO checker; for bank accounts the IBAN checker.
What a valid result does and does not prove
A passing checksum only shows that the number is well-formed. It does not prove that the number was ever issued, that it belongs to the person in front of you, or that you are allowed to process it. Belgian law regulates who may use and store national register numbers, so check your legal basis before you keep them in a database. Never test with real people's numbers when fictional ones will do.
Privacy
This page processes the number only in your browser and never logs or transmits it. Use fictional test data in development.
Frequently asked questions
How does the Belgian national number checksum work?
Take the first nine digits as a number, divide by 97 and subtract the remainder from 97. The result must equal the last two digits. For people born in 2000 or later a 2 is put in front of the nine digits first.
What is the difference between a rijksregisternummer, INSZ and NISS?
Rijksregisternummer and numéro de registre national are the national register number. INSZ (Dutch) and NISS (French) are the umbrella term for the social-security identification number, which is either a national register number or a BIS number.
How can I tell whether a number belongs to a man or a woman?
Look at the three-digit sequence number after the birth date. Odd means male and even means female. BIS numbers with an unknown sex use a month offset of 20 and carry no reliable sex information.
Why does a valid-looking number fail the check?
Most often a digit was mistyped, the year was read in the wrong century, or extra characters were copied with the number. Retype it and check whether the birth date matches the person.
Is my national number sent to a server?
No. The validation runs entirely in your browser and nothing is logged or stored.