Registered Office vs. Mailing Address: A Guide to Belgian Company Law in Brussels

Setting up a business in Brussels is an exciting gateway to the European market. However, one of the first hurdles entrepreneurs face is choosing an official address. In Belgium, this isn’t just a logistics choice—it is a critical legal requirement.

Misunderstanding the difference between a Registered Office and a Mailing Address can lead to heavy fines or even the forced closure of your company. This guide breaks down everything you need to know to stay compliant with Belgian law.

What is a Registered Office (Siège Social)?

In Belgium, your Registered Office (known in French as the Siège Social) is the “legal home” of your company.1 It is much more than just a place to receive letters; it is the official headquarters where your company’s “brain” resides.

Belgium follows the “Real Seat Theory.” This means that for tax and legal purposes, your company is considered to be located where its central administration and management actually happen.2 To be valid, your registered office must be the place where:

• The Board of Directors meets.

• Shareholders hold their general assemblies.

• The company’s central accounting files are kept.

Can I use a P.O. Box as my company address?

The short answer is no. A simple mailing address or P.O. Box (boîte postale) is strictly for receiving mail and has no legal standing for company registration. The Crossroads Bank for Enterprises (KBO/BCE)—the official Belgian business registry—will reject any application that uses a P.O. Box.

Why a P.O. Box is insufficient:

• Accessibility: Authorities, bailiffs, and creditors must be able to physically visit your office to deliver legal documents.

• Legal Service: A bailiff cannot legally serve a court summons to a locked mailbox in a post office.

• Banking: Most Belgian banks will refuse to open a business account if you cannot provide a physical address for your “real seat.”

Registered Office vs. Mailing Address: At a Glance

What are the risks of a “Fictitious Seat” (Siège Fictif)?

If you register an address where no real business activity or management takes place, the Belgian authorities may label it a Fictitious Seat. This is viewed as an attempt to hide from the law or evade taxes.

The consequences of being caught with a fictitious seat are severe:

1. Judicial Dissolution: A court can force your company to shut down permanently.

2. Tax Penalties: Authorities may re-evaluate your taxes, often adding surcharges ranging from 10% to 200%.

3. Personal Liability: Directors can be held personally responsible for the company’s debts and may face criminal charges for forgery.

   How do I register my address with the KBO?

Once you have a physical location (either through a lease or a regulated domiciliation provider), you must follow these steps to make it official:

1. The Notary (for SRL/SA companies)

A notary drafts your Deed of Incorporation, which includes your registered office address.4 This is then published in the Belgian Official Gazette (Moniteur Belge).

2. The Business Counter (Guichet d’Entreprises)

You must visit an accredited Business Counter (like Liantis, Xerius, or Securex) to activate your Enterprise Number.5 They will ask for Proof of Occupancy, such as a signed lease or a domiciliation contract.

3. VAT and Social Security

Once the KBO activates your number, you can apply for a VAT number. Note that the VAT administration may visit your address to verify that your business actually exists there.

How Domiciliation Services keep you compliant

Many startups and international firms use Regulated Domiciliation Services instead of renting a full private office.6 Providers like Interoffices offer a legal way to establish a registered office without the high overhead of a traditional lease.7

Under the Anti-Money Laundering (AML) Law of 2017, these providers act as “compliance gatekeepers.” A valid domiciliation contract provides:

• Physical Substance: You gain access to meeting rooms and coworking spaces, proving to tax authorities that your “real seat” is active.

• Privacy: It allows you to keep your private home address off the public KBO records.

• Legal Security: These providers are registered with the FPS Economy and perform “Know Your Customer” (KYC) checks, ensuring your business address is prestigious and fully legal.

Establishing a Branch as a Foreign Company

If you are a foreign business looking to open a branch in Brussels, the rules are slightly different but equally strict:

• You must register an “Establishment Unit” in the KBO.

• You must provide translated copies of your home country’s articles of association.

• You must appoint a legal representative based in Belgium.

Note: The address of this branch will determine how much Belgian corporate tax you pay on profits earned within the country.

How Interoffices Solves the Registered Office Challenge

For businesses that need a professional presence without the overhead of a traditional office lease, Interoffices provides a “compliance-first” solution. By offering registered business addresses and virtual office packages, they bridge the gap between legal necessity and operational flexibility.

A Valid Registered Office (Siège Social)

Unlike a standard mailbox, an Interoffices registered business address is fully compliant with the KBO/BCE requirements. Because Interoffices is a regulated provider, their contracts are recognized by Belgian Business Counters and Notaries as valid “Proof of Occupancy.” This ensures your company is built on a solid legal foundation from day one.

Virtual Office Solutions with Physical Substance

To avoid the risks of a “fictitious seat,” you must show that your business has a physical presence. The Interoffices Virtual Office package goes beyond simple mail handling. It includes:

• On-Demand Meeting Rooms: Access to professional spaces at prestigious locations like Avenue Louise or Brussels Airport to hold your official board meetings.

• Professional Multilingual Reception: A team to handle your calls and greet visitors or state officials, ensuring your business is always “accessible” as required by law.

• Seamless KYC Compliance: Interoffices handles the necessary Anti-Money Laundering (AML) checks, giving your business instant credibility with banks and tax authorities.

By using these services, you ensure that your “real seat” of management is documented and verifiable, protecting you from the legal and fiscal pitfalls of non-compliance.