Checking a supplier's tax debts in Belgium: how it works

Many Belgian clients only check whether a supplier owes social security contributions to the NSSO. But the withholding obligation has two parts. Besides social debts, it also matters whether your supplier has tax debts with the FPS Finance. Forgetting that second part is a separate and very real risk.

Why the NSSO is only half the check

The rules for construction and similar work rest on two separate systems:

Both are calculated on the invoice amount excluding VAT. A supplier can be fully in order with the NSSO and still owe tax. In that case you must withhold 15%, even if the NSSO status is green.

What counts as a tax debt

These are tax debts established by the FPS Finance that are due, such as:

• unpaid corporate or personal income tax;
• unpaid VAT;
• payroll withholding tax that was not remitted.

A debt under dispute or covered by a payment plan can be treated differently. That is why you always rely on the official result on the day of payment, not on what the supplier tells you.

How to check, step by step

1. Look up the enterprise number. It is on the invoice or in the Crossroads Bank for Enterprises. Use the full ten digit number.
2. Consult the official withholding service. The government offers an online lookup that shows, per enterprise number, whether there is a tax and or social withholding obligation.
3. Read both parts separately. The result shows the NSSO and the FPS Finance apart. Look at both.
4. Check on the day of payment. A result from last month does not protect you.
5. Keep the proof with date, time and reference in the payment file.

Worked example

A supplier sends an invoice of 20,000 euro excluding VAT. The check shows a tax debt but no social debt.

If the supplier also has a social debt, another 35% goes to the NSSO, 50% in total. For the next steps, read our guide on a supplier subject to withholding.

What happens if you forget

If you pay the full invoice while a tax withholding obligation existed, you become jointly liable for your supplier's tax debts, up to 35% of the total price of the work excluding VAT. The FPS Finance can also claim the amount you should have withheld directly from you.

Both parts in one go

With the withholding obligation check you check the social and tax status of all your suppliers together. Checkplicht repeats the check automatically, emails you as soon as a supplier becomes subject to withholding and keeps a PDF proof with date and official reference for every check. For the social side in detail, read checking social security debts.

Frequently asked questions

Do I need a tax check if the NSSO status is fine? Yes. The two parts are independent. A green NSSO status says nothing about tax debts.

How much do I withhold for a tax debt? 15% of the invoice amount excluding VAT, remitted to the FPS Finance.

Does this also apply to small invoices? The obligation applies to construction work and certain designated sectors, regardless of the invoice amount.