Short answer: In Belgium, indexation is a right, not an obligation. A landlord who never asks for it simply forgoes the increase — your rent legally stays where it is. They can start indexing at any future lease anniversary, and they can backdate a claim, but only by about three months for a residential lease. Once a valid indexation is requested, the tenant does have to pay it.
Why isn't my rent going up?
Many Belgian tenants notice that their rent has stayed the same for years and wonder if something is wrong. Usually nothing is wrong at all. Rent indexation — the annual adjustment to the official health index (gezondheidsindex / indice santé) — is a right the landlord may exercise, not a duty. If the landlord never sends a written indexation request, the increase simply does not happen and the rent stays at its current amount.
Landlords forgo indexation for all sorts of reasons: they forget the lease anniversary, they manage the property casually, they want to keep a reliable tenant happy, or they never registered to track the index. None of this makes the tenancy irregular. The rent you are paying is fully legal.
Can a landlord suddenly start indexing again?
Yes. Skipping indexation one year does not waive it forever. At the next lease anniversary the landlord can send a written request and begin indexing going forward. Two things are worth understanding:
- The formula always refers back to the original starting index — the health index of the month before the lease was signed. So if a landlord never indexed for several years and then finally requests it, the new rent generally jumps to reflect the full accumulated index change since the start of the lease, not just one year. That single step can feel large.
- Backdating is strictly limited. For a residential lease, the landlord can only claim the higher (indexed) rent for roughly the last three months before the written request — not for all the years they skipped. If they request indexation on 1 October, they can claim the difference for July, August and September, but not for the months before that.
So the level can catch up in one move, but the back-payment cannot: years of missed indexation are lost to the landlord, capped at about three months.
Do I have to pay if my landlord asks later?
If the request is valid, yes — indexation is a legal right and cannot simply be refused. A request is valid when the lease is registered, the amount follows the official health-index formula, it is applied on the lease anniversary, and it respects any regional cap. In recent years Flanders, Brussels and Wallonia each linked indexation to the property's energy performance certificate (EPC/PEB), and those rules differ by region and have changed over time — so a low-energy-label property may be entitled to only a reduced indexation. Check the current rule for your region before paying or before charging.
What you do not owe is retroactive back-rent beyond the ~3-month window, or any amount above what the formula produces. If a landlord suddenly demands several years of back-payments, that part of the claim is generally not enforceable.
What should you do?
If you are the tenant: don't panic if an indexation arrives after years of silence — check that it lands on your anniversary, recompute it with the free indexation calculator (French: indexation du loyer), and confirm any backdating is capped at three months. Ask for the calculation in writing if anything looks off.
If you are the landlord: forgetting indexation quietly erases income you cannot fully recover — the retroactive window is only three months. The fix is simply to track each lease anniversary and send the request on time, every year. That is exactly the kind of thing a management tool handles for you.
Frequently asked questions
Is my landlord obliged to index the rent in Belgium?
No. Indexation is a right, not an obligation. A landlord who never requests it simply forgoes the increase, and the rent legally stays at its current amount. The tenancy remains completely regular.
My landlord skipped indexation for years — can they claim it all back?
No. For a residential lease, backdating is limited to roughly the last three months before the written request. The landlord can start indexing going forward and the rent level can catch up to the current index, but the missed years of back-payments cannot be reclaimed.
Do I have to pay indexation if my landlord asks after a long gap?
Yes, if the request is valid — lease registered, correct health-index formula, applied on the anniversary, and within any regional energy-label cap. Indexation is a legal right and cannot simply be refused. You do not owe back-rent beyond about three months, though.
Why would a landlord choose not to index the rent?
Often they forget the anniversary, manage the property informally, or want to keep a good tenant. Because indexation is not automatic, nothing happens unless the landlord actively sends a written request each year.
Can a landlord raise the rent by more than indexation to make up for lost years?
No. Outside the health-index formula, a landlord cannot unilaterally raise a running residential rent. They can only apply the legal indexation, which references the original starting index — so the level may rise in one step, but not beyond what the formula produces.
Never lose income to a forgotten indexation
ImmoDesk tracks every lease's anniversary, fetches the official Statbel health index, calculates the correct indexed rent, and generates a compliant indexation letter in Dutch or French — so landlords never quietly lose income, and tenants always get a figure they can verify. Start free — no credit card required, or try the free calculator first.
This article is general information about Belgian residential rent indexation as of 2026 and is not legal advice. Rules differ by region (Flanders, Brussels, Wallonia) and change over time — verify the current rule for your situation or consult a professional.
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