Rent indexation calculator (Belgium)
Calculate the annual indexation of your rent from the legal Belgian formula: base rent × new health index ÷ starting index. Enter the indices published by Statbel and the new rent falls out; the French side uses the INSEE IRL index instead. A rent is a private figure, so the calculation stays on your device.
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This tool runs entirely in your browser — nothing is sent to a server.
In Belgium, the rent of a registered lease can be indexed once a year, on the anniversary of the lease taking effect, using the legal formula: base rent × new index ÷ starting index. The indices used are the health indices published monthly by Statbel.
The starting index is the one for the month preceding the lease signature; the new index, the one for the month preceding the lease anniversary. This tool applies the formula and shows the new rent and the increase in percent.
How it works
Type the figures or drop the file you want to process — the tool checks them as you go.
Everything is computed directly in your browser. Nothing is sent to a server.
The result appears instantly, with the detailed breakdown ready to copy, download or keep.
Why use this tool
No account, no download, no limit: the result appears as soon as you enter your data.
Every rule, algorithm and check reflects what we use ourselves every day at Flexina.
The calculations follow the official standards, and the step-by-step detail lets you double-check the outcome.
What does running it locally bring you?
Files, figures and documents never leave your device: nothing is stored, nothing is sent.
Once the page is loaded, you can cut the network: the tool keeps working.
No upload, no account, no third-party server in between: results stay fast and fully private.
Frequently asked questions
Which indices should I use?
The health index (not the consumer price index), in the base in force, published by Statbel. Starting index: the month before the lease signature; new index: the month before the lease anniversary.
Is the indexation automatic?
No: the landlord must request it in writing. It is not retroactive beyond 3 months and requires a written, registered lease.
Does this formula also apply in France?
No. In France, the revision uses the IRL (rent reference index) published by INSEE, with a different formula. This tool applies the Belgian rule.