What is my Belgian national register number and where do I find it?

It is an 11-digit personal ID number in the format YY.MM.DD-XXX.XX. Once you have your Belgian eID or residence card, it is printed on the front and stored in the card's chip. Before the card arrives, your commune will give you the number in writing after your first registration appointment.

Can I open a bank account or start a job without a national register number?

Not properly. Belgian banks, your employer's payroll, the tax authority and the mutuelle all need this number to identify you. You may be able to register with your commune and begin the process, but the number is what unlocks each of these steps, so getting registered quickly is the priority.

What is a bis number and how is it different?

A bis number is an 11-digit identifier issued by the Crossroads Bank for Social Security (BCSS/KSZ) to people who have dealings with Belgian authorities but are not entered in the National Register (for example cross-border workers who live abroad). It looks like a national number except the birth-month digits are increased by 40 (or 20 if sex is unknown at issue). Most residents get a real national number, not a bis.

How long does it take to get the number after I arrive?

You must report to your commune within 8 working days of arriving. Many communes give you a provisional national register number at or shortly after that first appointment, but full registration also depends on a neighbourhood police check confirming you live at your address, which can take several weeks.

Your Belgian National Register Number (Numéro National / Rijksregisternummer)

What the Belgian national register number is, its YY.MM.DD-XXX.XX format, how you get one at your Brussels commune, and why it gates banking, tax and itsme.

If one piece of paper controls your entire arrival in Belgium, it is this: your national register number (French: numéro de registre national or numéro national; Dutch: rijksregisternummer). Almost nothing — bank account, salary, health cover, tax, even logging into government websites — works without it, so understanding what it is and how to get it early will save you weeks of frustration.

What the number actually is

Your national register number is a unique 11-digit identifier assigned to everyone entered in Belgium's National Register (the population and foreigners registers held by the communes). It follows this format:

YY.MM.DD-XXX.XX

The first six digits are your date of birth, written year-month-day (so someone born on 4 March 1990 starts 90.03.04).
The next three digits (XXX) are a sequence number. It is odd for men and even for women.
The last two digits (XX) are a check number that mathematically validates the first nine, so the system can catch typos.

Within Belgian social security this same number is called your NISS (numéro d'identification de la sécurité sociale) / INSZ. National register number and NISS are the same 11 digits for ordinary residents — don't be thrown by the different name on different forms.

Where it appears

Once you are registered and your card is produced, the number is:

Printed on the front of your Belgian eID or residence card (the titre de séjour / verblijfskaart), and stored in the card's chip.
On your SIS-equivalent health data, your payslips, tax documents and most official letters.
Retrievable via the federal MyBEID / MyGov help centre once you have an account.

Before the physical card arrives, your commune gives you the number in writing at or shortly after your first appointment — keep that slip of paper safe and photograph it.

Why it gates everything

Belgium runs on this number. Here is what genuinely depends on it:

You want to…	Why the number is needed
Open a bank account	Banks are legally required to identify you; the national number is the key identifier they record.
Get paid a salary	Your employer's payroll and social-security declarations (Dimona/DmfA) are filed against your NISS.
Join a mutuelle / mutualité / ziekenfonds	Belgium's mandatory health insurance is registered under your national number.
Do your taxes	The FPS Finance systems (Tax-on-web, MyMinfin) link everything to it.
Use itsme® and government portals	itsme and Belgian public services read the national number that is stored only on a Belgian eID.
Sign contracts	Leases, phone contracts and utilities routinely ask for it.

That last point matters more than expats expect. To activate itsme® — the digital-identity app you'll use to log into your bank, your commune, MyMinfin and dozens of other services — you generally need either a Belgian eID or a Belgian bank card. The national register number is the piece of data that ties the whole digital identity together, and it is stored on the Belgian eID specifically.

How and when you get it

You do not apply for the number directly — it is created when your commune registers you. The sequence in Brussels looks like this:

Report to your commune within 8 working days of arriving. Non-EU nationals and EU/EEA nationals planning to stay more than three months must register in person at the maison communale / town hall of the commune where they live. This first step is the déclaration d'arrivée / aangifte van aankomst. Check which commune you're in first — the City of Brussels covers postal codes 1000, 1020, 1120 and 1130 (and part of 1040/1050), but Brussels-Capital has 19 separate communes, each with its own town hall.
You receive a national register number. Many communes issue a provisional national register number at or soon after this appointment so administrative steps can begin.
A neighbourhood police check. To confirm you actually live at your stated address, the commune asks the local police to visit. These visits happen at random times — daytime, evenings, weekends — and the officer usually wants to see you in person. Make sure your name is on the letterbox.
Positive report → full registration. If the report is positive, you are entered in the appropriate residents' register, and your eID / residence card is ordered.
Collect and activate your card. Your PIN and PUK codes arrive by post to your registered address. You then return to the commune to collect the physical card and activate it with your PIN.

For some categories of foreigner a federal fee (redevance) applies at registration; the amount depends on your situation, so check the current figure on your commune's page rather than trusting a number you read on a forum.

Provisional and "bis" numbers explained

Two things confuse newcomers:

A provisional national register number is simply your real number issued before the police check and card are complete. It is a normal national number — keep using it.
A bis number (numéro bis / bisnummer) is different. It is issued by the Crossroads Bank for Social Security (BCSS / KSZ) to people who deal with Belgian authorities but are not entered in the National Register — for example cross-border workers who work in Belgium but live abroad. Its format mirrors the national number except the birth-month digits are increased by 40 (or by 20 if the person's sex is unknown when it's created). If you are moving to and living in Brussels, you should normally end up with a proper national register number, not a bis.

Common problems and fixes

"I need a bank account to activate itsme, but a national number to open the bank account." Register with your commune first — that produces the number. Some banks will start onboarding on your provisional number; ask before assuming you must wait.
The police never came. Chase your commune. The visit is on you to enable: correct name on the letterbox, and be reachable at the address. Without a positive report, your registration stalls.
The number is wrong on a document. Because the last two digits are a checksum, a single transposed digit will fail validation. Ask the issuer to re-check against your eID or commune slip.
You have both a bis and a national number. This happens if a Belgian body identified you before you moved (e.g. you worked here first). Flag it to your commune and to any institution using the old bis number so records can be linked to your national number.

Your next step

Before you do anything else administrative in Brussels, book your commune registration appointment for the correct one of the 19 communes and go within 8 working days of arriving. Everything downstream — bank, salary, mutuelle, itsme — flows from the number that appointment sets in motion. Confirm your commune's exact requirements and any fee on its official page: brussels.be/registration-foreigner.