Indexation is strictly limited to the health index
No, the landlord cannot apply a rent increase above what the indexation formula yields. Only the health index published by Statbel can be used. Any lease clause providing for a higher increase is deemed unwritten (legally void).
The restrictions are clear:
- Only the health index (indice sante) can be used — not the CPI or any other index
- The formula cannot be modified by contract
- No additional percentage can be added on top of the formula result
- Any clause providing otherwise is automatically void
Examples of invalid indexation clauses
These lease clauses are legally void and unenforceable:
- “The rent will be increased by 3% annually” (arbitrary percentage, not formula-based)
- “The rent will follow the consumer price index” (wrong index — must be health index)
- “The rent will be indexed at 110% of the health index evolution” (multiplication above formula)
- “The landlord may adjust the rent at their discretion” (no discretionary power)
If your lease contains such a clause, the legal formula applies instead. The invalid clause is simply ignored.
If your landlord applies an increase above the health index formula, you can contest it by providing the correct calculation based on official Statbel data. You are only obliged to pay the amount resulting from the legal formula.
What to do if the landlord charges above the formula
If you suspect your landlord is indexing above the legal formula:
- Recalculate using the official formula with Statbel indices
- Compare your result with the amount the landlord is requesting
- Notify the landlord in writing of the discrepancy
- Pay only the correct amount — you are not in default for paying the legally calculated indexed rent
- Request reimbursement of any overpayment
- If needed, refer the matter to the Justice of the Peace
Regional specifics
Brussels-Capital Region
Under the Ordinance of 27 July 2017, indexation above the health index is void. Additionally, EPC restrictions may further limit indexation below the formula result.
Wallonia
The Decree of 15 March 2018 applies the same rule. Invalid indexation clauses are deemed unwritten.
Flanders
The Flemish Housing Rental Decree of 9 November 2018 confirms that only the health index formula is valid. Any deviating clause is void.
Article 1728bis of the Belgian Civil Code — the formula is mandatory and cannot be modified by contract. Deviating clauses are deemed unwritten pursuant to the same article.