Formal notice letter (refusal of indexation)
To use when your tenant disputes or doesn't pay the indexation after your initial notification. It is the mandatory step before referring to the justice of the peace.
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Avenue Louise 367
1050 Brussels
RECIPIENT (to send by registered mail)
Jean Vandenberghe
Rue Haute 142
1000 Brussels
Subject: Formal notice to pay the due indexation — Rue Haute 142, 1000 Brussels
Dear Sir or Madam,
By letter dated 1 July 2026, I notified you of the annual indexation of the rent relating to the property you occupy under the lease signed on 14 June 2021.
As of today, 45 days after this notification, the indexed rent supplement remains unpaid. I hereby formally notify you to proceed with payment as soon as possible.
I remind you that under article 1728bis of the Belgian Civil Code, indexation is a right for the landlord as soon as the lease is registered and the request has been made in writing — which is the case here.
Awaiting your payment, yours faithfully.
Signature,
Marie Dupont
When to send a formal notice?
Three typical situations that justify a formal notice:
- The tenant doesn't pay the supplement — they continue to pay the old rent after your indexation notification.
- The tenant disputes the calculation — they write to you that they disagree with the amount.
- The tenant ignores your letter — no response, no full payment, no explicit dispute.
Registered mail mandatory
Unlike the simple indexation notification (which can be sent by simple letter), the formal notice must be sent by registered mail with acknowledgment of receipt. This proof of dispatch will then allow referring to the justice of the peace.
Without registered mail, the judge will not be able to consider that the tenant has been duly formally notified — your action risks being rejected for procedural defect.
And after the 15 days?
If the tenant has still not regularised after the deadline given in the formal notice:
- Refer to the justice of the peace of the property's commune (free procedure)
- Attach the documents: registered lease, initial notification letter + acknowledgment of receipt, formal notice letter + acknowledgment of receipt, detailed calculation of the indexation
- Quick hearing: 4-8 weeks on average
- Judge's decision: if your calculation is correct, the tenant is ordered to pay the supplement + the costs (procedural fees)
Frequently asked questions
When to use this letter? + −
When the tenant disputes or doesn't pay the indexation after your first notification. It's the step before referring to the justice of the peace.
What deadline to grant? + −
15 days from receipt of the registered mail. Reasonable and standard deadline for a formal notice. Beyond that, you can refer to the justice of the peace.
Should it be sent by registered mail? + −
Yes, mandatory. The formal notice has legal value only if sent by registered mail with acknowledgment of receipt. Without this proof, you cannot refer the case to the justice of the peace.
What if the tenant still doesn't pay after 15 days? + −
You refer to the justice of the peace of the property's commune. The procedure is free and quick (a few weeks). The judge decides: if your calculation is correct, the tenant is ordered to pay + costs.
Can the tenant refuse the indexation due to poor maintenance? + −
No. Maintenance and indexation are two separate matters. The tenant who complains about maintenance can bring another action in court, but cannot unilaterally refuse to pay the indexation.
Related templates
- Initial notification letter — to send first
- Registered mail slip — to attach
- Complete example