Each year, on the anniversary date of the lease, the rent may be indexed according to a precise legal formula. Since 2022, the rules have changed: the EPC certificate now influences the indexation amount in all three Belgian regions. Here is the complete guide to calculating your new rent, region by region.
Calculate your indexation in a few clicks with our free calculator — it takes into account your region, your EPC rating, and all the rules currently in force.
What is rent indexation?
Indexation is the legal mechanism that allows the rent to be adjusted to the evolution of the cost of living, measured by the health index published each month by the FPS Economy (Statbel). It is not a free rent increase: it is a legally governed adjustment based on a mathematical formula.
Indexation only applies under the following conditions:
- The lease is in writing (not oral)
- The lease does not contain a clause excluding indexation
- Indexation is requested on the anniversary date of the lease's entry into force (or within the following 3 months, no later)
- The landlord makes the request — indexation is never automatic
The calculation formula
The legal formula is identical in all three Belgian regions:
New rent = Base rent x (New index / Base index)
Base rent: the initial rent agreed in the lease (excluding charges).
New index: the health index for the month preceding the anniversary date of the lease's entry into force.
Base index: the health index at a reference date that depends on the region and the date of signature of the lease.
The result is always rounded up to the nearest cent. Indexation can never exceed the result of this formula — no additional "margin" is permitted.
The base index by region
This is where regional differences begin. The choice of base index directly affects the indexation amount.
Brussels and Wallonia
The base index is the health index for the month preceding the signing of the lease. This is the classic rule, inherited from Article 1728bis of the Civil Code.
Example: lease signed on 15 March 2020 → base index = health index for February 2020.
Flanders
Flanders has introduced a distinction with the Flemish Residential Tenancy Decree:
- Leases signed from 1 January 2019 onwards: the base index is the health index for the month preceding the entry into force of the lease (not the signing date)
- Leases signed before 2019: the classic rule applies (month preceding signing)
This distinction matters when the signing date and the entry into force date differ by several months.
The impact of the EPC certificate on indexation
Since the 2022–2023 reforms, all three Belgian regions have introduced mechanisms limiting indexation for energy-intensive properties. These measures aim to incentivise landlords to renovate.
Brussels — correction factors
The ordinance of 14 October 2022 (Brussels Housing Code, Art. 224) introduces correction factors that reduce indexation for poorly rated properties:
| EPC | Correction factor |
|---|---|
| A to D | 100% (full indexation) |
| E | Correction factor depending on the anniversary month |
| F and G | More restrictive correction factor |
The correction factor depends on the anniversary month and progressively reduces the permitted indexation. For an EPC E property, the reduction is moderate. For EPC F or G, it can almost entirely cancel indexation.
Important: this restriction only applies to leases signed before 14 October 2022. Leases signed after that date are not affected (the landlord is assumed to have incorporated the energy performance into the initial rent).
Wallonia — adjusted base rent
The Walloon decree of 19 October 2022 (amending the decree of 15 March 2018, Art. 26) introduces the concept of an adjusted base rent. Rather than reducing the indexation percentage, Wallonia caps the base rent used in the formula.
For EPC D, E, F, and G properties, the base rent is replaced by a lower adjusted rent, calculated in two phases:
- Phase 1 (November 2022 to October 2023): initial restriction with a reduced base rent
- Phase 2 (since November 2023): the adjusted base rent is recalculated, generally more restrictive
The result: even if the health index rises, since the calculation base is capped, the new rent remains contained.
Flanders — permanent correction factor
The decree of 10 March 2023 (Flemish Residential Tenancy Decree, Art. 34) imposes a permanent correction factor for EPC D, E, and F certificates:
| EPC | Correction factor |
|---|---|
| A+ to C | 1.0 (full indexation) |
| D | 0.975 (2.5% reduction) |
| E | 0.950 (5% reduction) |
| F | 0.900 (10% reduction) |
This factor is applied directly to the result of the standard formula. Unlike Brussels, it is fixed and does not vary over time.
Condition: the lease must have been signed before 1 October 2022 for the restriction to apply.
Special cases
Commercial leases
Commercial leases follow the standard indexation formula (Article 1728bis of the Civil Code), without any EPC restriction. The energy corrections introduced in 2022–2023 only concern residential leases.
The formula therefore remains:
New rent = Base rent x (New index / Base index)
The base index is always that of the month preceding the signing, regardless of the region.
Unregistered leases
Lease registration is free and mandatory for residential leases. Absence of registration has consequences for indexation:
- Wallonia: an unregistered lease cannot be indexed at all. This is a direct sanction provided for under Walloon legislation.
- Brussels: indexation is possible, but only from the date of actual registration of the lease.
- Flanders: no specific restriction linked to registration for indexation.
Retroactivity
Indexation can only be claimed retroactively for the 3 months preceding the written request. If the landlord forgets to index for several years, they can only recover 3 months of arrears.
Calculate your indexation for free
Rather than looking up indices, applying EPC corrections, and checking regional rules manually, use our free indexation calculator.
Simply enter:
- The type of lease (residential or commercial)
- Your region
- The EPC rating of the property
- The base rent
- The signing date and entry into force date
The calculator automatically applies the correct formula, the correct indices, and the EPC corrections currently in force. You obtain your new rent in a few seconds, with a detailed explanation of the calculation.
Managing several properties? SEIDO automates indexation across your entire portfolio: notification on each anniversary date, pre-filled indexation letter, lease and EPC tracking.
Frequently asked questions
Is indexation mandatory?
No. Indexation is a right of the landlord, not an obligation. If the landlord does not request it on the anniversary date, the rent remains unchanged. The tenant is never required to propose indexation.
Can a rent already indexed the previous year be indexed again?
Yes. Indexation is always calculated on the base rent (the initial rent in the lease), never on the indexed rent from the previous year. The formula always uses the base rent as the starting point.
What if my EPC rating changes after renovation?
If you obtain a better EPC certificate following works, the correction factor is updated at the next indexation. Moving from EPC F to EPC C, for example, restores full indexation.
Does indexation apply to service charges?
No. Indexation only concerns the base rent, never service charges (whether fixed or provisional). Charges are adjusted separately under the terms of the lease.
Which index to use: health index or consumer price index?
Rent indexation in Belgium uses the health index, which is a smoothed version of the consumer price index excluding certain products (tobacco, alcohol, motor fuel). It is the index published monthly by Statbel.
Can my tenant refuse indexation?
If the legal conditions are met (written lease, correct formula, request on the anniversary date), the tenant cannot refuse indexation. In the event of a dispute, the justice of the peace has jurisdiction.
Last updated: March 2026. This article is provided for information purposes only and does not constitute legal advice. For any specific situation, consult a qualified property law professional.