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How to calculate the indexation of residential rent in Belgium

Rent indexation in Belgium is based on a simple but precise legal mechanism. The principle is to adjust the amount of the rent according to changes in the health index, an indicator that reflects changes in consumer prices excluding certain sensitive products. This helps protect both the tenant and the owner against the erosion of purchasing power or an excessive increase.

The key elements for properly understanding rent indexation

Review the clauses of your lease agreement

Indexation only applies if the lease provides for it. Usually, a specific clause states that the rent will be indexed annually on the basis of the health index. Without that mention, the rent remains fixed, even if the index rises. You will often find the reference period used for the calculation in that clause.

Defining the reference period for indexation

The reference period refers to the timeframe over which health indices are compared. It is usually based on a rolling year or a period specified in the lease. For instance, the March index for the current year can be compared to that of March in the previous year. This directly affects the outcome of the calculation.

The health index: the basis for calculating indexation in 2026

The health index is published every month by FPS Economy. It is this index, and not the general price index, that is used for the legal revision of rents. It excludes certain food products and energy, which makes it more stable and better suited to measuring changes in the cost of living for housing.
https://statbel.fgov.be/en/themes/consumer-price-index/health-index

Calculating residential rent indexation correctly

The formula is simple: the new rent is equal to the old rent multiplied by the ratio between the new index and the old index.
Use the following formula to calculate the indexation:
New rent = Old rent x (new index / old index) 
In this formula, the new index is the health index of the current reference period, and the old index is the health index of the previous reference period.
Accuracy is essential: you must choose the exact indices corresponding to the periods defined in the lease. A small error can lead to an incorrect amount and therefore to disputes.

Complying with the legal deadlines for applying indexation

The law requires the tenant to be notified in writing at least one month before the new amount takes effect. This notification must clearly state the old rent, the new health index used, the calculation performed and the new amount. Without this formality, the indexation cannot be applied.

The specific regional and legal rules in 2026

In recent years, the rules have evolved differently across regions. For example, restrictions may apply depending on the property’s energy performance (EPC). Some regions even limit or suspend indexation to encourage renovations. It is therefore important to check the rules in force in your region, whether in Brussels, Wallonia or Flanders.
Because of these regional differences, there is no single rule for the whole of Belgium. The local authorities regularly publish updates that you should consult before applying the indexation.

With TREVI, benefit from automatic and secure indexation

TREVI handles your rent indexation, removing the need to manage calculations or administrative steps. The system automatically uses official health indices and applies the appropriate method, while factoring in regional and legal requirements. This reduces the risk of errors and ensures each revision is compliant.
You receive a clear notification with the details of the applied indexation, which ensures transparency and peace of mind. Our advisers can help you gain more clarity if you have any doubts about your situation.

FAQ

  • How does rent indexation work in Belgium ?

    Rent indexation in Belgium allows rental prices to be updated according to the health index, ensuring the landlord’s income keeps pace with inflation. This process is strictly regulated and relies on a specific calculation tied to the regularly published index.

  • Is a tenant allowed to refuse rent indexation in Belgium ?

    No, rent indexation in Belgium is typically automatic and legally regulated, so tenants cannot refuse it when the lease contains an indexation clause. That said, exceptions may exist depending on the lease conditions or any agreements between both parties.

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