What does Belgian law say about rent indexation?

Brief answer

Belgian law on rent indexation now rests on three texts, one per region: in Brussels, article 1728^bis of the former Civil Code and article 224/2 of the Brussels Housing Code; in Wallonia, article 26 of the decree of 15 March 2018 on residential leases; in Flanders, article 34 of the Vlaams Woninghuurdecreet (leases concluded since 1 January 2019; article 1728^bis for older written leases). The formula is common, but the starting index is that of the month preceding the signature in Brussels and Wallonia, and of the month preceding the entry into force in Flanders (leases concluded since 2019). Since the sixth state reform (2014), the three regions each add their mechanisms (EPC correction factors in Brussels and Flanders for certain leases that entered into force before autumn 2022; in Wallonia, limitation period ended on 31/10/2023, but a permanent special method remains for the EPC D to G leases limited in 2022-2023 — 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
• A retroactive effect limited to the three months preceding the month of the request

In substance, the text provides that the rent is adapted to the cost of living once a year, on the anniversary date of the lease’s entry into force, on the basis of the health index and on the landlord’s written request.

2. Law of 6 August 1993 on lease contracts

This federal text is complemented, since regionalisation, by conditions specific to each region:

• Lease registration: in Brussels and Wallonia, the lease must be registered; in Flanders, a written lease is enough
• Consequence of non-registration (Brussels, Wallonia): no indexation is due 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 — EPC certificate provided to the tenant as a condition (§ 1), in addition to the registered lease; § 1/2: correction factor for leases that entered into force before 14 October 2022 with an EPC E, F or G (ordinances of 13 October 2022 and 13 October 2023)
• Flanders: Vlaams Woninghuurdecreet, art. 34 (leases concluded since 1 January 2019: written lease, written request, starting index of the month preceding the entry into force); decree of 3 October 2022 — correction factor for contracts that entered into force before 1 October 2022 (EPC D, E, F or no EPC)
• Wallonia: decree of 15 March 2018 on residential leases, art. 26 (formula, starting index of the month preceding the signature; written and registered lease required), amended by the decree of 19 October 2022 (still in force) — limitation period until 31/10/2023, then a permanent special method (calculation from the adapted rent) for the EPC D to G or uncertified leases limited in 2022-2023; ordinary formula for all others

Regional detail on our Wallonia, Brussels and Flanders pages.

The official formula step by step

The three regional texts use the same formula, always calculated from the base rent:

Indexed rent = Initial rent × (Health index of the month preceding the anniversary of the entry into force ÷ Starting index)

The starting index is that of the month preceding the signature of the lease in Brussels (art. 1728^bis) and Wallonia (art. 26 of the decree of 15 March 2018); in Flanders, for leases concluded since 1 January 2019, it is that of the month preceding the entry into force (art. 34 of the Vlaams Woninghuurdecreet).

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 — our calculator handles five bases (1988, 1996, 2004, 2013, 2025); base 2025 applies to leases signed from 1 January 2026

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 mechanisms)
« 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: a written lease is required in all three regions

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
3 October 2022	Flemish decree	Temporary EPC-based limitation (1/10/2022 → 30/9/2023), then correction factor since 1/10/2023
13 October 2022	Brussels ordinance (in force on 14/10/2022)	Temporary EPC-based limitation (14/10/2022 → 13/10/2023)
19 October 2022	Walloon decree (still in force)	Temporary EPC-based limitation (1/11/2022 → 31/10/2023)
13 October 2023	Brussels ordinance (in force on 14/10/2023)	Correction factor for leases in force before 14/10/2022 (EPC E, F, G)
31 October 2023	End of the Walloon period (decree of 19/10/2022)	Ordinary formula, except special method for the limited EPC D to G leases
1 January 2026	Base 2025 of the health index	Used for leases signed from 1/1/2026 (our calculator handles five bases: 1988, 1996, 2004, 2013, 2025)

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. Regional conditions — in Brussels and Wallonia, is the lease registered? Free verification via MyMinfin (« My real estate » section). In Brussels, was the EPC certificate provided to the tenant? In Flanders, a written lease is enough
2. Calculation — is the formula respected? Our calculator returns the exact indexes and the official result
3. Regional mechanism — does an EPC correction factor (Brussels, Flanders) or the Walloon special method apply? Depends on the region, the certificate and the date the lease entered into force (see 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 (Brussels Housing Code, Walloon decree of 15 March 2018, Vlaams Woninghuurdecreet) — be.brussels, Wallex and codex.vlaanderen.be
• 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 — registration condition in Brussels and Wallonia
• 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.