Knowledge base

Practical guides on the Belgian withholding obligation.

nsso·9/22/2026·7 min read

Declaration of works to the NSSO: when, how and why

Anyone having immovable works carried out in Belgium must declare them to the NSSO beforehand. Here is who declares, within what deadline, through which channel and what happens if you forget.

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nsso·9/16/2026·7 min read

Requesting an NSSO certificate: who, where and how long it is valid

Step by step: which document you need for a withholding obligation check, where to request it and how long it stays valid.

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nsso·9/1/2026·7 min read

How to find your supplier's NSSO number: a guide for clients

Finding your supplier's NSSO number is the first step of every withholding obligation check. Here are the four most reliable ways, plus the pitfalls to avoid.

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nsso·8/20/2026·7 min read

Checking social security debts: step by step

How to correctly check a contractor's social security and tax debts: what you need, how to read the result and what to do when an amount must be withheld.

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