Knowledge base
Practical guides on the Belgian withholding obligation.
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.
Supplier subject to withholding: what to do at payment
Your check flags the withholding obligation. Here is how much to withhold, who to transfer it to, which certificate can lower the amount and what proof to keep.
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.
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.
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.
Belgian withholding obligation for contractors: complete 2026 guide
Everything about the Belgian withholding obligation in 2026: when to check, how much to withhold, who to pay and how to avoid penalties.