It is the once-a-year adjustment of the rent to the cost of living, measured by the health index. It is the legal default for a written residential lease: it applies unless the lease explicitly excludes it, and no indexation clause is needed for it to exist. It is not automatic — the landlord has to ask for it in writing — and it can be applied at the earliest on the anniversary of the lease coming into force.

new rent = base rent × (new health index ÷ starting health index). The base rent is the rent written in the lease, excluding charges and costs paid by the tenant. It is the ratio of the two index figures that matters, which is why both must be expressed in the same base year.

The new index is the health index of the month preceding the anniversary month — never the anniversary month itself. The starting index is the health index of the month preceding the start of the lease. In Flanders the decree ties that to the month before the lease entered into force; in Brussels and Wallonia the official guidance refers to the month before signature. If you signed in one month and moved in another, that difference matters — check the rule for your region.

No — and this is the mistake landlords make most often. You always index from the original base rent in the lease and the original starting index, never from last year's already-indexed amount. The rent still rises with cumulative inflation, because the new index keeps climbing, but re-indexing an indexed rent overcharges the tenant.

Once per rental year, at the earliest on the anniversary of the lease entering into force. Not twice, not on 1 January for everyone, and not on a date the landlord finds convenient.

No. It is an indicative tool, not legal advice. Belgian rent law is regionalised and changes regularly. Always check the result against the official regional calculator and the exact wording of your lease before applying or paying an indexation.

It is the consumer price index with a few products removed: alcoholic drinks (in a shop or in a café), tobacco, and motor fuels — except LPG. It has been published monthly since January 1994 and is the figure used for rent, wages and social benefits.

No, and mixing them up is a classic error. The smoothed index (afgevlakte index / indice lissé) is a four-month moving average, used for the pivot-index mechanism that triggers wage and benefit increases. Rent indexation uses the ordinary monthly health index. In any given month the two figures are different.

Base 2013 = 100 for the whole series, from January 1994 to the most recent published month. Using one base for both figures is what keeps the ratio — and therefore the result — correct.

From January 2026 the Belgian CPI and health index were rebased to 2025 = 100, so the freshly published figures look much smaller than the ones in your lease. It does not change what you are owed, but you must not mix bases: a base-2013 starting index divided by a base-2025 new index understates the rent by roughly a third. Convert one side first — the published conversion coefficient for the health index is about 1.3557 from base 2025 to base 2013 (and about 0.7376 the other way) — or simply use the built-in table here, which is entirely on base 2013.

Statbel publishes the index for a month at the end of that same month, normally around the 26th. So an anniversary early in the month is calculated from a figure that has been available for weeks; an anniversary on the 1st still needs the previous month's figure, which is already out.

The law phrases the result as a ceiling — the adapted rent may not be higher than base rent × new ÷ starting. If the health index dropped, the formula produces a lower rent, and the party with an interest can request that adjustment in writing. In practice a landlord will simply not ask in a deflation year, so a tenant who wants the reduction has to request it themselves.

Yes. A verbal lease cannot be indexed — the Flemish decree makes the written form an explicit condition, and the same logic applies elsewhere: without a written base rent and a written start date there is nothing to index from.

In Brussels and Wallonia registration is an explicit legal precondition: an unregistered lease may not be indexed, and a tenant can reclaim indexation already paid. In Flanders the housing decree does not list registration among the conditions in its indexation article, although some sources say otherwise. Registration is compulsory and free in any case, and it is the landlord's obligation for a residential lease — so register, and the question does not arise.

Yes, in all three regions. Indexation only happens if the interested party requests it in writing. An email or a message can be enough, but registered post is what you will want if it is ever disputed. A model letter is available on the Walloon housing site and most tenants' associations publish one too.

No. Indexation works back at most three months before the month of the written request. A landlord who forgets for three years recovers a quarter of a year, and the rest is gone permanently. From the next anniversary onwards the rent is at the correct indexed level again — the loss is the back payment, not the level.

Yes. The parties are free to agree that the rent will not be indexed, or will be indexed less than the law allows. They cannot agree to more than the legal formula — a clause going further is reduced to the legal maximum.

Yes. For a written residential lease indexation is the legal default; the clause is not what creates the right. Its absence changes nothing, whereas an explicit exclusion does.

During the 2022 energy crisis all three regions decided that landlords of badly insulated homes should not fully benefit from index-driven rent increases while their tenants were paying the energy bill. Each region did it differently, on different dates, and the temporary measures have since expired — but two of the three left a permanent trace.

Between 1 October 2022 and 30 September 2023, a lease on a home with EPC label D could only be indexed for half the increase, and a home with label E, F or no valid EPC could not be indexed at all. That window has closed.

Not necessarily. Since 1 October 2023 a correction factor applies at every subsequent indexation, for leases that entered into force before 1 October 2022 on a home with label D, E, F or no valid EPC. Its purpose is to make the frozen year permanent — without it the rising index would quietly recover the whole freeze at the next anniversary. The rule as adopted has no end date.

Two ways: obtain a better EPC label for the property, or start a new lease. Leases that entered into force on or after 1 October 2022 index normally whatever the label says.

That was announced as policy by the Flemish government in November 2024 — no indexation for EPC E and F from 2028, and no letting them at all from 2030. As far as we can establish it has not been enacted as a decree yet. Treat it as a strong signal about where Flanders is going, not as a rule that applies today, and check the current text before you rely on it.

Full indexation, no correction, no complications. The energy-crisis measures only ever touched D and below.

The 2022 twelve-month measure (label E at half, F and G blocked) expired on 13 October 2023 and was replaced by a system of correction factors that is still in force. It applies to leases that took effect before 14 October 2022 on a property whose certificate is rated E, F or G. The standard formula result is multiplied by a factor that depends on the label and on the month of the anniversary.

They run roughly from 0.945 to 0.990 for label E and from 0.891 to 0.980 for labels F and G, depending on the anniversary month — a reduction of between one and eleven percent of the indexed rent. The official table is published on be.brussels, and that is the version to use if there is any money at stake.

Yes — a valid certificate must exist and have been communicated to the tenant at the moment indexation is requested. No certificate, no indexation for the labels concerned.

Nothing, energy-wise. The Walloon PEB limitation applied only to anniversaries between 1 November 2022 and 31 October 2023 (D at 75%, E at 50%, F/G/no certificate blocked) and has fully expired. Since 1 November 2023 the PEB score has no effect on the right to index or on the amount.

Yes — a level effect. For leases whose anniversary fell inside the 2022–2023 window, the reduced rent from that period becomes the baseline for later indexations, so the freeze is not recovered afterwards. Wallonia publishes a dedicated FAQ on that specific calculation; use it rather than a rule of thumb.

Because residential rent law was regionalised in 2014, and each region legislated separately during the energy crisis with its own dates, its own labels and its own arithmetic. It is genuinely three regimes, which is why a single national answer to “can I index?” does not exist.

The base rent from the lease, the region, the energy label, the date the lease came into force and the anniversary date you are indexing on. The two index figures fill themselves in from the built-in table once the dates are set — the auto-fill button does it in one click.

The original base rent written in the lease, before any indexation, and excluding charges. If you enter the currently indexed rent the result will be too high, because the formula would then compound.

That month has not been published yet. Statbel publishes each month's index around the 26th of that month, so an anniversary very early in a month may need a figure that appears only days before. Wait for publication, or enter the figure by hand once it is out.

The federal Statbel calculator is authoritative but limited: it states itself that it can be used as-is only for properties with an energy label A, B or C — plus label D in Brussels. For D and below elsewhere you are sent to the regional sites. This tool applies the regional corrections in one place, which is convenient — and precisely why you should verify a result that carries a correction factor against the official regional source.

No. The index table, the formula and the regional rules are all part of the page, and the calculation runs in your browser. Nothing you type is transmitted or stored, which matters because a rent, an address and a lease date together say quite a lot about you.

Yes, once the page has loaded. Everything it needs, including thirty-two years of monthly index values, is already in the page.

Only on legal grounds. Valid ones: the lease is not registered where registration is required, the calculation uses the wrong months or the wrong index, a regional correction factor was ignored, or more than three months of retroactivity is claimed. Not valid: the rent already feels high, you were not warned in advance, or money is tight. Refusing without a legal ground puts you in default on the rent.

Probably not all of it. Belgian law applies a short prescription period to indexation: claims relating to the index adjustment — both the landlord's arrears and the tenant's overpayment — prescribe in about a year rather than the five years that apply to rent generally. Act quickly and get advice; do not assume you have five years.

The justice of the peace (vrederechter / juge de paix) of the place where the property is, which is the cheap and accessible court for rental disputes. Before that, a tenants' association or a mediation service will usually resolve an arithmetic disagreement in one conversation.

Indexing last year's indexed rent instead of the base rent in the lease. It looks harmless in year two and is badly wrong by year six. The second most common is using the anniversary month's index instead of the month before it.

Assuming the increase is illegal because it arrived without warning, and simply not paying. Indexation does not need advance notice beyond the written request itself. Check the arithmetic first — that is where the real errors are.

Ask for it. You are entitled to know which base rent, which two index figures and which months were used, and a landlord who has done it correctly can supply all four in one line. A request that cannot be explained is usually a request that is wrong.

A residential lease of three years or less follows the same indexation regime: once a year, on the anniversary, same formula, same regional corrections. The differences between short and nine-year leases are about notice and duration, not about indexation.

Different regime entirely. Commercial leases are governed by the federal law of 1951, which contains no automatic indexation: the rent can only be indexed if the lease actually contains an indexation clause. Where it does, the health index is the usual reference and it applies once a year. No EPC or PEB correction factor applies to commercial leases in any region.

It does not work like this at all. Social rent is calculated from the tenant's income and recalculated every year, not indexed under the residential-lease rules. This calculator does not apply to a social lease; your housing company is the source of truth.

Student leases and shared-housing arrangements are separately regulated in each region and often for a fixed term of one year, where the question of an anniversary indexation rarely comes up. Where a longer student lease does allow indexation, the health-index formula is the same — but check the regional student-lease rules first.

A furnished let that is the tenant's main residence follows the residential rules, including indexation. Short holiday lets are not main-residence leases at all and fall outside this regime entirely.

Statbel for the index itself and the federal rent calculator; be.brussels for Brussels including the correction-factor table; wallonie.be for Wallonia including a model letter; and the Vlaams Woninghuurdecreet on Codex Vlaanderen for Flanders. Tenants' associations and the justice of the peace handle the cases the websites do not cover.