How is rent indexation calculated in Belgium?

The formula is: New rent = Base rent × (New health index ÷ Starting index). The starting index is that of the month before the lease was signed. The new index is that of the month before the anniversary date.

When can rent be indexed?

Indexation is possible each year on the anniversary date of the lease coming into effect, provided the contract is written and does not exclude it. The request must be made in writing to the tenant.

Is the indexation calculation the same in Wallonia, Brussels and Flanders?

The formula is identical in all three regions. However, specific rules limit indexation based on the EPC of the property, with a schedule specific to each region since 14 October 2023.

Does the EPC prevent rent indexation?

Since 14 October 2023, a weak EPC (E, F or G depending on the region) can limit or prohibit indexation. The rules vary between Wallonia, Brussels and Flanders.

Rent indexation calculator: free tool Belgium

Q: Can indexation be retroactive?

No. Indexation must be requested in writing within three months of the anniversary date. After this deadline, it is no longer retroactive for elapsed months.

How does our indexation calculator work?

Our tool follows the official method of FPS Finance. You enter three pieces of information:

The base rent amount stated in the lease agreement.
The lease signing date (or the date the contract came into effect).
The anniversary date on which you are indexing.

The simulator automatically calculates the result. No need to look up the health index yourself — everything is built in.

What is rent indexation in Belgium?

Rent indexation allows the rent to be adjusted to reflect changes in the cost of living. In Belgium, the calculation is governed by the Civil Code. Indexation is only possible if:

The lease agreement is written.
The lease covers a primary residence, student housing, or includes an indexation clause.
A full year has elapsed since the anniversary of the lease coming into effect.

For a deeper understanding, see our complete guide to rent indexation.

The official indexation formula

The formula used for calculating rent indexation in Belgium:

New rent = Base rent × (New health index ÷ Starting index)

Base rent: the rent set in the lease agreement.
Starting index: the health index of the month before the lease was signed.
New health index: the index of the month before the anniversary date.

Price indices are published monthly by Statbel.

Rent indexation calculation example

Take a lease signed in March 2024, rent of €900.

Health index February 2024 (starting index): 129.23
Health index February 2025 (new index): 132.47
New rent = 900 × (132.47 ÷ 129.23) = €922.56

The calculation results in an increase of €22.56 per month.

Rent indexation calculation 2025 and 2026

The rules remain stable, but indices change monthly. Our calculator is updated automatically. You always get an up-to-date calculation without having to look up indices yourself.

Indexation must be requested in writing from the tenant, within three months of the anniversary date. After this deadline, it is no longer retroactive.

EPC and indexation: rules since 14 October 2023

Since 14 October 2023, the energy performance of the property affects the right to index.

Indexation in Wallonia

In Wallonia, properties rated F or G see their indexation limited or prohibited. Properties rated A to E can be indexed normally.

Indexation in Flanders

Flanders applies similar rules, with its own timeline. Energy-inefficient properties are progressively regulated.

Indexation in Brussels

Brussels has specific regulations for rents of energy-inefficient properties. Properties rated E, F or G are affected — a stricter threshold than Wallonia.

Rules by region

The three Belgian regions apply different rules:

Region	Legal framework	EPC prohibits indexation
Wallonia	Walloon Decree	F, G
Brussels	Brussels Housing Code	E, F, G
Flanders	Flemish Decree	F, G

Our calculator adapts to the region of the property to ensure a reliable result.

Why use our tool?

Our simulator offers:

A precise result in 10 seconds.
Indices updated in real time.
Automatic adaptation to your region.
PDF export of the result to send to your tenant.
History of previous indexations.

Also discover our other tools: rental yield simulator, inventory generator.

Ready to calculate your indexation?

Use our calculator now and send the new rent to your tenant in just a few clicks.