Rental lawIndexing the rent: when, how, how much
The exact formula, the health index, the anniversary date, the fact that nothing is automatic and retroactivity is capped, and what the EPC still changes in 2026, Region by Region.
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Indexing is not a rent increase
Indexation is not a revision. It does not reward works, it does not track the market: it simply preserves the purchasing power of the agreed rent by tying it to price movements. The base rent never changes; only the amount payable is recalculated each year, starting from that base rent.
For a main-residence lease, the conditions are, as a rule:
Registration is in any case compulsory and free in all three Regions: see our guide to lease registration.
The formula
New rent = base rent × new health index ÷ starting health index
- Base rent: the rent agreed at signature, excluding charges. Not last year's indexed rent: you always restart from the original rent, otherwise indexation would compound on itself.
- Starting index: the health index of the month preceding the month of signature.
- New index: the health index of the month preceding the anniversary of the lease's commencement.
The health index is the consumer price index without alcoholic drinks, tobacco and motor fuels (petrol and diesel). It is calculated every month by Statbel, the Belgian statistical office. That is where the exact value comes from; or use Statbel's rent calculator directly, which looks up the right months' indices from the lease dates.
A worked example
Lease signed in May, commencing 1 June. Base rent: EUR 900 excluding charges. Starting index: April's, in the year of signature. On 1 June of the following year, you take the health index of May of that year.
If the starting index is 128.50 and the new index 131.60: 900 × 131.60 ÷ 128.50 = EUR 921.71, about EUR 22 more per month. Two years later, you will again start from EUR 900 and from the April index of the signature year, never from EUR 921.71.
These figures are illustrative: use the indices actually published by Statbel.
When? Once a year, on the anniversary
Indexation may occur only once a year, at the earliest on the anniversary of the lease's commencement. Not on the signature date, not on 1 January: on the commencement date. A lease that started on 15 September is indexed from 15 September each year.
It is not automatic, and retroactivity is capped
This is the rule landlords discover too late: indexation must be requested in writing. Until a request has been sent to the tenant, the indexed rent is not owed. And when the request arrives late, its retroactive effect is capped: it reaches back only over the three months preceding the month of the request.
A landlord who "forgets" to index for four years and then claims the whole backlog runs straight into that cap. He can index going forward and recover at most three months. The rest is lost.
Landlord's tip: set an annual reminder a week before the anniversary and send a plain letter (or a written, dated message) stating the base rent, the starting index, the new index, the calculation and the new amount. A tenant accepts an indexation that is explained; he contests one that lands without justification.
Tenant's tip: redo the maths. The most frequent errors are indexing from the already-indexed rent, instead of the base rent, or using the wrong month's index. Both inflate the figure.
The EPC can still limit indexation
During the 2022 energy crisis, all three Regions froze or reduced the indexation of poorly rated homes for a year. The freeze is over, but it left rules that differ from one Region to the next:
| Region | Prior condition | What the EPC changes in 2026 |
|---|---|---|
| Brussels | Registered lease and a valid EPC certificate given to the tenant | No EPC, no indexation. Lease that commenced before 14 October 2022 and EPC E, F or G: correction factor at every indexation |
| Wallonia | Registered lease | Indexation possible again for all labels since 1 November 2023. For EPC D to G, the calculation starts from the rent adjusted during the limitation period: what was not indexed then is not recovered |
| Flanders | Written lease | Lease that commenced before 1 October 2022 and label D, E or F (or no EPC): correction factor at every indexation |
In Wallonia the limitation ran from 1 November 2022 to 31 October 2023: full indexation for EPC A to C, 75% for D, 50% for E, none for F, G or without a certificate.
Flanders has also announced its intention to ban, from 2028, the indexation of homes rated E or F. Check how far that text has progressed before relying on it, either way.
Concretely:
What indexation is NOT
- Rent revision: it requires the parties' agreement, or a decision of the justice of the peace, within precise time windows (generally at the end of a three-year period of a main-residence lease) and on limited grounds (new circumstances, works that raised the rental value).
- A charges increase: provisions may move with real costs; that is a different mechanism, unrelated to the health index (see rental charges).
- A new rent imposed on renewal: a renewed lease continues on the same terms. It is not an opportunity to raise the rent. The rent of a new lease is set differently: see our guide to setting the rent.
In summary
| Point | Rule |
|---|---|
| Calculation base | Original rent, excluding charges, never the already-indexed rent |
| Starting index | Health index of the month before signature |
| New index | Health index of the month before the anniversary |
| Frequency | Once a year, at the earliest on the anniversary of commencement |
| Automatic? | No, written request by the landlord |
| Retroactivity | Capped at the three months preceding the month of the request |
| Registration | A condition for indexation in Brussels and Wallonia |
| EPC | No indexation without an EPC in Brussels; correction factor for some older leases, rule specific to each Region |
Letting with an EPC in order
If you let a property, the EPC label is more than a compulsory line in the ad: in Brussels, without a valid certificate given to the tenant, you cannot index. State it from the ad onwards, for example on Domilinko, a Belgian peer-to-peer rental site with no intermediary, where the listings' EPC certificates and owners' identity are verified, and the move-in inspection is done jointly, with photos and meter readings. Our guide to letting your property covers the other steps.
Compatri does not let housing and plays no part in your lease: this guide helps you understand your rights and find the right people to turn to.
Official sources
- Statbel: health index: official monthly values
- Statbel: rent calculator: applies the indexation formula from the lease dates
- Brussels Housing: rental price indexation: registration, EPC certificate and correction factor
- Wallonia: indexing a rent: registration and calculation for EPC D to G since 1 November 2023 (in French)
- Huurdersbond: rent indexation in Flanders: conditions and EPC correction factor (in Dutch)
Frequently asked questions
How is rent indexation calculated?
New rent = base rent (excluding charges, the original one) times the new health index, divided by the health index of the month preceding signature. The new index is that of the month preceding the commencement anniversary. Never restart from the already-indexed rent. Depending on the Region and the EPC label, a correction factor may then apply.
Is indexation automatic?
No. The landlord must request it in writing. Until he does, the indexed rent is not owed. And a late request has retroactive effect only over the three months preceding the month of the request: indexing four years late does not recover four years of arrears.
Can rent be indexed if the dwelling has a poor EPC?
Yes in principle, but not always at 100%. In Brussels no indexation is possible without a valid EPC certificate given to the tenant, and leases that commenced before 14 October 2022 with an EPC E, F or G are subject to a correction factor. In Flanders a correction factor applies to leases that commenced before 1 October 2022 with label D, E or F. In Wallonia indexation has been normal again since 1 November 2023, but the loss during the limitation is not recovered for EPC D to G. Check the rule with your Region's official source.
Must the lease be registered before the rent can be indexed?
In Brussels and Wallonia, yes: registration is a condition for indexation, and in Brussels the landlord must also have given a valid EPC certificate. In all three Regions, registering a main-residence lease is in any case compulsory, free, and the landlord's responsibility.
On what date can the rent be indexed?
Once a year only, at the earliest on the anniversary of the lease's commencement, not the signature date and not 1 January. A lease that started on 15 September is indexed from 15 September each year.
What is the health index?
It is the consumer price index without alcoholic drinks, tobacco and motor fuels (petrol and diesel). Calculated monthly by Statbel, the Belgian statistical office, it is the reference for indexing rents. Always use the official published value, or Statbel's rent calculator, never an estimate.