What does Belgian law say about rent indexation?

Brief answer

Belgian law on rent indexation rests on two federal pillars: article 1728^bis of the Civil Code (formula and principle right) and the Law of 6 August 1993 on lease contracts (application conditions, mandatory registration, written request). Since the sixth state reform (2014), the three regions each add their modulations (EPC coefficients in Brussels and Flanders; in Wallonia, capping window ended on 31/10/2023, but a permanent adapted method remains for capped EPC D-G leases — decree of 19/10/2022, still in force).

The 4 key texts to know

1. Article 1728^bis of the Belgian Civil Code

It is the legal foundation of indexation. Inserted into the Civil Code by the law of 20 February 1991, it lays down:

• The landlord’s right to request indexation once per year on the anniversary date
• The obligation of a written request (simple letter, registered or electronic)
• The mathematical formula based on the health index published by Statbel
• The effect at receipt by the tenant — never retroactively before this date

The exact text (excerpt):

« § 1^er. Unless otherwise agreed in writing, the rent is adapted to the cost of living once per rental year, on the anniversary date of entry into force of the lease. (…) The adaptation is based on the consumer price indexes. »

2. Law of 6 August 1993 on lease contracts

This law frames the substantive conditions of indexation:

• Mandatory registration of the lease within 2 months following signature (art. 5^bis)
• Sanction in case of non-registration: no right to indexation as long as regularisation is not done (our unregistered lease guide details the procedure)
• Notification modalities: free form but traceable (registered mail recommended in practice)
• Articulation with successive leases: a new lease starts on its own index base

3. Royal Decree of 24 December 1993

The RD introduced the health index as a specific basis for rent indexation, instead of the general consumer price index (CPI). The health index excludes:

• Fuels (petrol, diesel, heating oil)
• Tobacco
• Alcohol

This exclusion aims to neutralise price shocks linked to these products, which are highly volatile and do not reflect ordinary cost of living. In practice, the health index follows the CPI within 0.3 points over the long term.

4. Regional codes (since 2014)

With the sixth state reform, the regions are competent for residential leases. Each region added its own normative layer:

• Brussels: Brussels Housing Code, art. 224/2 §1^bis/2 — EPC coefficient for leases prior to 14/10/2022
• Flanders: decree of 4 July 2023 — permanent EPC coefficient for all leases
• Wallonia: decree of 19 October 2022 (still in force) — capping window until 31/10/2023, then a permanent adapted method for capped EPC D-G leases

Regional detail on our Wallonia, Brussels and Flanders pages.

The official formula step by step

Article 1728^bis imposes this formula:

Indexed rent = Initial rent × (Health index of the month preceding the anniversary ÷ Health index of the month preceding the signature)

Three important precisions:

1. « Month preceding » means strictly prior — if the lease was signed on 15 June, the reference index is that of May, not June
2. The « initial rent » is the one written in the lease, excluding charges and excluding security deposit
3. The health index must be from the right statistical base — Statbel simultaneously publishes 4 series (1996, 2004, 2013, 2025) and each lease uses the base in force at its signature date

For the detail of successive bases and the conversion table, see our methodology or directly the calculator which automatically applies the right base.

What the law DOES NOT IMPOSE (the false myths)

Many received ideas circulate. Here is what the law does not say:

Myth	What the law really says
« Prior notice is required before the anniversary date »	No prior deadline imposed
« Indexation must be notified by registered mail »	Free form — simple letter suffices
« The landlord must index every year or loses their right »	Waiver allowed, no precedent
« There is a federal cap in percentage »	No cap (except regional EPC coefficients)
« The tenant can refuse if they find the rent too expensive »	Invalid ground, probable conviction
« Indexation is calculated on the general CPI »	No, on the specific health index
« A verbal lease can be indexed »	No, due to impossibility of registration

For valid (and invalid) refusal grounds, see our can one refuse? guide.

Recent legislative evolutions (2022-2026)

The matter has moved a lot between 2022 and 2024 due to post-Covid inflation:

Date	Text	Effect
14 October 2022	Brussels ordinance (transitional)	EPC coefficient for old Bxl leases
19 October 2022	Walloon decree (still in force)	Capping window for EPC D-G leases (1/11/2022 → 31/10/2023)
4 July 2023	Flemish decree	Permanent EPC coefficient in Flanders
31 October 2023	End of the Walloon capping window	Permanent adapted method remains for capped EPC D-G leases (decree of 19/10/2022)
1 January 2026	New Statbel base 2025	Recalibration of the health index for new leases

Federal law (1728^bis) has not been modified, but its application conditions now vary from one region to another. This is precisely the object of our regional pages.

How to verify that an indexation complies with the law?

Three sequential checks:

1. Registration — is the lease registered? Free verification via MyMinfin (« My real estate » section)
2. Calculation — is the formula respected? Our calculator returns the exact indexes and the official result
3. Regional coefficient — does an EPC coefficient apply? Depends on the region and lease date (see tables in our cap guide)

If the three checks are positive, the indexation complies. If one fails, the tenant has a valid ground for contestation before the justice of the peace.

Official sources to consult

To go to the source, the integral texts are available on:

• Civil Code, art. 1728^bis — Justel database (Federal Public Service Justice)
• Law of 6 August 1993 — Belgian Official Journal of 7 October 1993
• RD of 24 December 1993 — Belgian Official Journal of 31 December 1993
• Regional decrees and codes — websites of respective regional parliaments
• Statbel health index — statbel.fgov.be (monthly update, around the 26th)

To go further

• When can one index a rent? — annual calendar and frequency rules
• Unregistered lease: consequences — sanction of art. 5^bis of the 1993 Law
• Can an indexation be refused? — legal refusal grounds
• Calculate the official indexation — direct application of texts
• Complete methodology — detailed legal sources
• Wallonia indexation, Brussels, Flanders

Belgian law on indexation is, in its federal principle, stable since 1993. But the regional variations since 2022 now require reasoning region by region — what the texts did not say 10 years ago.