The tenant refuses the indexation: what to do?

Answer in brief

When a tenant refuses the indexation, everything depends on their motive. Three motives are legally valid: unregistered lease, miscalculation, or retroactivity over 3 months. All other motives (landlord’s oversight, tenant’s financial situation, rent “already too high”) are invalid and the landlord can assert their right up to the justice of the peace.

The VALID refusal motives

A refusal of indexation is legally founded in three precise cases. In these situations, the landlord will not win the case before the justice of the peace as long as the motive is not lifted.

Unregistered lease: indexation not due

The lease’s registration with the competent registration office is mandatory within 2 months of the signature, at the landlord’s charge. Without registration, the right to indexation does not exist, regardless of the elapsed duration.

It is the most radical effect of the absence of registration: the tenant can refuse the indexation without compensation or notice, and the landlord has no remedy as long as the lease is not regularised. Our guide on unregistered leases details the retroactive registration procedure and its tax consequences.

Miscalculation: recalculation necessary

If the landlord made an error in the calculation (wrong index month, formula misapplied, incorrect reference month), the tenant has the right to refuse the exact requested amount. They are not refusing the indexation in principle — they are refusing an incorrect calculation.

The most frequent errors:

• Index of the signature month instead of the month preceding the signature
• Raw health index instead of the smoothed one (or vice versa, depending on the lease)
• Anniversary date based on the move-in date instead of the signature

Our step-by-step guide on indexation calculation explains each step with a worked example. In case of doubt, the official calculator automatically applies the correct formula.

Retroactivity over 3 months: impossible

Article 1728bis, §1 of the Belgian Civil Code limits the retroactive effect of the indexation request to the 3 months preceding the month of the request. If the landlord tries to claim 3, 5 or 8 years of retroactive indexation, the tenant can legitimately refuse the part beyond the last 3 months.

Our dedicated article rent indexation after 5 years quantifies this effect: an 8-year oversight only entitles to 3 months recoverable, the rest is permanently lost. A partial refusal on this basis is legally founded.

The INVALID refusal motives

All other motives don’t hold up before the justice of the peace. Here are the three most frequent, with the counter-arguments to oppose in your reply letter.

”You should have warned me earlier”

Counter-argument: Belgian law imposes no notice before the lease’s anniversary date. Indexation is not automatic (it requires a written request), but it takes effect on the anniversary date as soon as the notification is made — not on a “courtesy” date chosen by the tenant.

Article 1728^bis of the Civil Code and the Law of 6 August 1993 on main residence leases mention no obligation of notice. The only constraint is the retroactivity limit: the request only reaches back to the 3 months preceding the month of the request (art. 1728bis, §1).

”The rent is already too expensive”

Counter-argument: the absolute amount of the rent is not a legal motive of refusal of indexation. Indexation follows a strict mathematical formula based on the health index published by Statbel. The “high” character of the rent is a subjective appreciation without legal basis opposable to the landlord.

If the tenant considers the rent disproportionate, they can request a rent revision at the justice of the peace at the triennial renewal of the lease (procedure distinct from indexation, subject to strict conditions).

”I have financial problems”

Counter-argument: the tenant’s financial situation is a human motive but not a legal one. The landlord remains entitled to demand the due indexation. However, it is often the right time to propose an amicable arrangement: spreading the difference over 6 or 12 months, temporary indexation freeze in exchange for a guarantee, etc.

A formal refusal on this motive will be rejected by the justice of the peace. But a written amicable compromise (lease addendum signed by both parties) sustainably protects the rental relationship.

Recommended procedure in 3 steps

Faced with a refusal of indexation, methodically follow this progression. Never go directly to court without having exhausted steps 1 and 2.

1. Verify your own calculation. Before responding to the refusal, redo the calculation on the official calculator. Verify: exact signature date, month of the reference index (month preceding the signature), month of the new index (month preceding the anniversary date), applied formula. An error on your side completely changes the deal — better correct it before hardening the tone.

2. Re-notify by motivated registered mail. Send a second written request, by registered mail with acknowledgment of receipt, containing: reference to article 1728^bis of the Civil Code and to the Law of 6 August 1993, calculation detail (used health indexes, formula, dates), new monthly rent, effective date, and PDF proof of the calculation as an attachment. This documented reminder often makes a good-faith tenant yield who had simply misunderstood.

3. Formal notice then justice of the peace. If the registered reminder remains without effect within 15 days, send a formal notice by registered mail, with a final 15-day deadline. Without response, refer to the territorially competent justice of the peace (property’s commune). The procedure is almost free, without mandatory lawyer.

The justice of the peace: what to expect

It is the Belgian jurisdiction competent for all rental disputes, including indexation refusal. Here is the concrete progression for a landlord who has never referred to this instance.

Cost: the procedure is free on the merits. Only a fiscal stamp of about 50 euros must be paid with the petition. No mandatory lawyer — you can represent yourself. Many landlords do.

Delay: hearing generally set in 4 to 8 weeks after filing the petition. The justice of the peace handles rental disputes as a priority.

Decision: if your calculation is correct and the lease registered, the judge orders the tenant to pay the due arrears within the limit of the 3 months preceding the month of the request, plus the new indexed rent from the effective date. The tenant is also ordered to pay the costs, which covers the fiscal stamp and any expenses of the landlord.

Concrete procedure example: Brussels lease of €950/month signed in March 2020. In March 2026, the landlord calculates the due indexation (new rent: €1,124). The tenant refuses by SMS invoking “an already too high rent”. The landlord sends a motivated registered reminder in late March (step 2). Without response, formal notice in mid-April (step 3). Without response, petition filed at the justice of the peace of Brussels in late April. Hearing on 12 June 2026, that is 6 weeks after filing. Decision: tenant ordered to pay 3 months of arrears (€522) + costs (€50), new rent effective since March 2026. Total cost for the landlord: €0, the fiscal stamp being reimbursed by the costs.

Useful letter templates

Three templates cover the entire refusal management procedure:

• Indexation notification to the tenant — the first request, to send each year on the anniversary date
• Formal notice letter — step 3 of the procedure, to send by registered mail with a 15-day deadline
• Registered mail slip — systematically to attach for formal proof of receipt date

All templates integrate the mandatory legal references (article 1728^bis of the Civil Code, Law of 6 August 1993) and the indexation calculation detail.

Going further

• How to calculate an indexation step-by-step
• Indexation after 5 years: retroactivity rules
• Unregistered lease: consequences on indexation
• Tenant notification letter template
• Complete calculation methodology