Commercial lease indexation requires a contractual clause
Yes, the rent of a commercial lease can be indexed, but only if the lease contains an explicit indexation clause. Without it, no indexation is possible. The applicable index is the consumer price index (not the health index used for residential leases). The landlord must actively claim the indexation each year — it is not retroactive.
Commercial lease law (Law of 30 April 1951) does not provide for automatic rent indexation. This is a fundamental difference from residential lease law, where indexation is a legal right. For commercial leases, indexation is a matter of contractual agreement between the parties.
This distinction reflects the principle that commercial parties negotiate on equal footing and should be free to determine whether and how rent adjustments occur. Many commercial tenants negotiate fixed rent periods or caps on indexation as part of their lease negotiations.
How to claim commercial lease indexation
| Step | Action |
|---|---|
| 1 | Verify the indexation clause exists in the lease |
| 2 | Identify the base index and reference month |
| 3 | Look up the current consumer price index |
| 4 | Apply the formula: Base rent x (New CPI / Base CPI) |
| 5 | Notify the tenant in writing |
| 6 | Apply the new rent from the following month |
Key rules:
- Indexation is claimed annually on the lease anniversary
- The landlord must notify the tenant in writing
- It is not retroactive — if the landlord forgets to claim for a year, that increase is lost
- The tenant can verify the calculation and challenge errors
Set an annual reminder for the lease anniversary to claim indexation. Missing even one year means that year’s adjustment is permanently lost. Keep a record of all indexation notifications and calculations.
Drafting an effective indexation clause
A well-drafted indexation clause for a commercial lease should include:
- Reference to the consumer price index (specify base year, e.g. base 2013 = 100)
- Base index — the index of the month preceding the lease start
- Indexation date — the anniversary of the lease entry into force
- Formula — explicitly state: New rent = Base rent x (New CPI / Base CPI)
- Notification procedure — how the landlord must inform the tenant
- Optional: cap on increase — some tenants negotiate a maximum annual increase (e.g. 3%)
Without specifying these elements, the clause may be too vague to enforce. Courts require sufficient precision to calculate the indexed rent without ambiguity.
Negotiation points for tenants:
- Annual cap on indexation (e.g. maximum 2% per year)
- Indexation holiday for the first years of the lease
- Downward indexation protection (floor clause)
Regional specifics
Brussels-Capital Region
Commercial lease law is federal and applies uniformly across Belgium. The Law of 30 April 1951 governs indexation of commercial leases in Brussels identically to other regions. No regional variation exists for commercial lease indexation.
Walloon Region
The same federal law applies. Any temporary residential rent indexation freezes imposed in Wallonia do not affect commercial leases. Commercial lease indexation follows purely contractual terms.
Flemish Region
Federal commercial lease law applies equally. Flemish measures limiting residential rent indexation (based on energy performance) have no effect on commercial leases.
Law of 30 April 1951 on commercial leases — Text on Justel. Law of 2 August 1966 (indexation mechanism). Commercial lease indexation is federal and contractual.