Indexation is a legal right for residential leases
Yes, for primary residence leases, rent indexation is a legal right that applies even without an explicit clause in the lease. The landlord must request it in writing — it is not automatic. For commercial leases and other non-residential contracts, an express indexation clause is required. The parties can contractually waive the right to indexation for residential leases.
Regional housing legislation in Belgium grants landlords the right to annual rent indexation based on the health index for all primary residence leases. This right exists by law and does not need to be written into the lease contract. The rationale is to protect landlords against inflation while maintaining tenant protections.
However, “legal right” does not mean “automatic.” The landlord must actively claim the indexation each year by notifying the tenant in writing. The indexed rent is due only from the month following the written request, not retroactively.
How to request indexation without a lease clause
Even without an indexation clause, the process is straightforward:
- Calculate the indexed rent using the formula: Base rent x (New health index / Base health index)
- Notify the tenant in writing — by letter, email, or any traceable means
- Apply from the following month — the indexed rent takes effect from the month after the request
- No retroactive claim — you cannot claim past indexation you did not request
| Situation | Indexation possible? |
|---|---|
| Written lease, no indexation clause | Yes (legal right) |
| Written lease, clause excluding indexation | No (valid waiver) |
| Verbal lease | Yes (legal right, but proof challenges) |
| Commercial lease, no clause | No (clause required) |
| Garage/parking lease, no clause | No (clause required) |
Even though no clause is legally required, it is best practice to include an indexation clause in the lease. This avoids misunderstandings and clearly informs the tenant that annual indexation will be applied. It also specifies the reference month for the base index.
When indexation is not possible without a clause
The legal right to indexation applies only to primary residence leases. Other lease types require an express clause:
- Commercial leases — governed by the Law of 30 April 1951, which does not provide automatic indexation
- Garage and parking leases — governed by ordinary contract law, no automatic indexation
- Office leases — governed by ordinary contract law
- Student housing — may follow residential rules depending on the region
- Short-term holiday rentals — not covered by residential lease legislation
Additionally, the parties can contractually waive the right to indexation in a residential lease. Such a waiver is valid if it is clear and unambiguous. The landlord then cannot claim indexation for the duration of the waiver.
Regional specifics
Brussels-Capital Region
The ordinance of 27 July 2017 confirms that rent indexation is a legal right for primary residence leases in Brussels, with or without a clause. Brussels has also introduced temporary energy-related indexation restrictions for properties with poor energy performance.
Walloon Region
The decree of 15 March 2018 provides the same legal right to indexation. Wallonia has adopted similar energy-related restrictions, temporarily freezing indexation for the worst-performing properties.
Flemish Region
The Vlaams Woninghuurdecreet of 9 November 2018 grants the same indexation right. Flanders has introduced indexation limits for properties with low energy performance certificates (EPC label E or F).
Regional housing legislation (Brussels ordinance 2017, Walloon decree 2018, Flemish decree 2018) establishing rent indexation as a legal right for primary residence leases. No clause required.