Belgium Rent Indexation: The Huurindexatie / Indexation du Loyer Formula by Region

Every year, a Belgian landlord who wants to raise the rent in line with inflation runs the same calculation: new rent equals the base rent, multiplied by the current health index, divided by the starting index. The formula itself is identical in Flanders, Wallonia and Brussels. What differs by Region, and differs enough to genuinely change the number, is which month each of those two index figures is read from, whether an energy label limits the result, and whether an unregistered lease can be indexed at all.

The single most common mistake is elsewhere, though, and it has nothing to do with Region. Base rent means the rent fixed when the lease was concluded. It is not last year's rent, and it is not last year's already-indexed figure. Indexing an already-indexed rent, rather than the original base rent, compounds the same error every year it happens.

Information last verified on 21 July 2026. This page provides general legal information and does not constitute legal advice in an individual case.

The formula, and the error that costs the most

The formula is the same across the whole country: new rent equals base rent, multiplied by the new health index, divided by the starting index. Both index figures are the gezondheidsindex, the indice santé, published monthly by Statbel, and it is the only index Belgian law recognises for rent indexation.

Base rent is the rent as fixed when the lease was concluded, never a figure from last year, and never an already-indexed amount. Applying the formula to last year's rent instead of the original base rent, even once, means every later indexation compounds the same mistake forward.

Enter your Region, your lease's start date, the base rent, and the date of the request, and the calculator below applies the correct starting month for your Region and works out the result.

Which month counts, and it genuinely differs by Region

Flanders: entry into force, both ends

Under article 34 of the Vlaams Woninghuurdecreet, the starting index is the health index of the month before the lease entered into force, and the annual anniversary that triggers a new indexation also runs from that same entry-into-force date. Both ends of the Flemish rule point at the same event.

Wallonia: signature for the start, entry into force for the clock

In Wallonia, the starting index is the health index of the month before the lease was signed, but the anniversary that decides which month the new index comes from is the anniversary of the lease ENTERING INTO FORCE, not of signature. Article 26 of the décret of 15 March 2018 is explicit about both halves. So Wallonia has the same mixed structure as Brussels: signature sets the starting index, entry into force sets the annual clock. Only Flanders uses a single anchor at both ends.

Brussels: signature for the start, entry into force for the clock

Brussels genuinely mixes the two reference points used separately in Flanders and Wallonia. The starting index is still the month before signature, matching Wallonia, and the annual clock that decides when a new indexation is due runs from entry into force, matching Flanders. Reading only one of the two rules and assuming it covers Brussels in full is the mistake this subtlety exists to prevent.

Frequency, and the written request Brussels alone extends

Indexation can happen at most once a year, on the lease's anniversary date under whichever rule above applies to your Region. It is not automatic in any Region: the landlord must request it in writing. Skipping a year does not let a landlord claim two years' worth of increase at once; a missed request is simply a missed year.

Brussels adds one further allowance not confirmed for the other two Regions: a request there can reach back retroactively, up to three months before the month in which it is made. Flanders has the same three-month cap, in article 34 §1 of the Vlaams Woninghuurdecreet: the adjustment applies only where the interested party asks in writing, and it reaches back no more than three months before the month of the request. For Wallonia we could not confirm the equivalent wording inside article 26 itself, so this page does not state a Walloon retroactivity window either way.

The health index, and reading both figures off the same base

Both the starting index and the current index are the gezondheidsindex, the indice santé, published monthly by Statbel. Its original base sets 2013 equal to 100.

Statbel has since re-expressed the series on three different bases, 2004, 2013 and 2025, side by side. That creates a genuine trap: a lease's starting index and its current index must be read off the same base as each other. Mixing a base-2013 starting figure with a base-2025 current figure produces a rent that is badly wrong, not just slightly off.

Energy labels: a Region-specific limit, not a single Belgian rule

Belgium has, at different times, limited how much a poor energy label lets a landlord recover through indexation, and the current position is genuinely different in each Region.

Wallonia. The PEB-based limitation ran only from 1 November 2022 to 31 October 2023. Since 1 November 2023, indexation is again possible at 100 percent for every label, with a special calculation built in specifically to stop a landlord recovering the frozen year retroactively.

Brussels. A correction factor applies only to labels E, F and G, and only where the lease took effect before 14 October 2022. There is no correction factor at all for labels A, B, C or D; a Brussels property with a D label is indexed on the ordinary, uncorrected formula. The coefficients themselves drift month to month, and the official calculation tool states it is valid only until 31 July 2026, so treat the current figures as subject to change rather than fixed.

Flanders. A correction factor applies to labels D, E, F and to leases with no EPC at all, where the lease was in force before 1 October 2022, following an earlier freeze that ran from 1 October 2022 to 30 September 2023. The mechanism itself is confirmed, but this page does not publish the numeric factor table or the 2028 cutoff sometimes quoted for it, because neither could be confirmed against an authority source. If your lease is Flemish and falls into this category, check the current factor directly with the Flemish administration rather than relying on a figure repeated elsewhere.

Registration: an unregistered lease can block indexation

Brussels and Wallonia both confirm the same rule on their own authority sources: an unregistered lease blocks indexation. In Wallonia this has applied since 1 September 2018, specifically where indexation would raise the rent.

Flanders almost certainly works the same way, but that position was not confirmed against a primary Flemish source at the time of writing. Treat it as highly likely rather than settled, and register your lease regardless, since registration itself is free and required for other reasons besides indexation.

This page provides general legal information about Belgian rent indexation and does not constitute legal advice for an individual case. The correct figures depend on your Region, your lease's exact dates and its energy label, and several of the rules described here change on stated dates. Confirm the current position with the competent regional administration, Statbel, or a notaris / notaire, before acting.