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.
Your check says a supplier is subject to the withholding obligation. You then cannot pay the invoice in full. You withhold part of it and transfer that part to the authority claiming the debt. Here is the full routine, with the amounts, the deadlines and the proof to keep.
What withholding means
You pay your supplier less than the invoice amount and the difference goes to the authorities. The supplier still treats the invoice as paid: your transfer counts as payment on their behalf.
| Type of debt | Who claims | Percentage | Base |
|---|---|---|---|
| Social security debt | NSSO | 35% | invoice amount excluding VAT |
| Tax debt | FPS Finance | 15% | invoice amount excluding VAT |
| Both | NSSO and FPS Finance | maximum 50% | invoice amount excluding VAT |
With both debts you withhold 35% plus 15%, so 50%, and transfer each part to the right authority.
Step by step for one invoice
- Check on the day of payment. Last week's situation does not count. Keep the date and the official reference of your check.
- Work out the amount to withhold, on the amount excluding VAT.
- Pay your supplier the balance, stating why the amount is lower.
- Transfer the withheld part, with the correct reference, to the NSSO or FPS Finance.
- Keep the proof: the check and its reference, the calculation, and proof of the transfer.
When you withhold less, or nothing
A supplier can ask the authority for a certificate showing the debt is lower than the amount you would withhold. With that certificate you withhold only the amount of the debt. Its validity is short, so it must be recent on the day you pay. Ask your supplier for the document and keep it with the payment file.
What it costs if you do not withhold
Pay an invoice in full while withholding was due and you become jointly liable for your supplier's debt, capped at the value of the works. On top of that comes an administrative fine equal to double the amount you should have withheld. An oversight of a few thousand euro can therefore cost a multiple.
Keeping this workable
The practical difficulty is not the calculation but the timing: the status can change between your last check and your payment. Three habits make the difference:
- Check automatically and periodically, not only at contract signing.
- Send an alert as soon as a supplier becomes subject to withholding, so bookkeeping can hold the payment.
- Keep a dated, referenced proof document per check, so nothing has to be reconstructed during an inspection.
Frequently asked questions
Do I withhold on advance invoices? Yes, the duty applies to every payment for immovable works, including advances and interim statements.
What if the supplier objects? Your transfer counts as payment. The supplier settles the debt with the authority, not with you.
Does this apply to foreign suppliers? Yes. Foreign companies carrying out immovable works in Belgium fall under the same rules, even when their details are not in the Belgian register.
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.
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.
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.