Short answer: Yes — in Belgium a landlord can increase the rent once a year through indexation, but only on the lease's anniversary date, only using the official health index, and only if they request it (it is not automatic). The increase is not a free choice: it follows a fixed legal formula, so the exact amount is predictable and can be checked in seconds.

What is rent indexation?

Rent indexation is the annual adjustment of the rent to the rising cost of living. In Belgium it is based on the health index (gezondheidsindex / indice santé), published monthly by Statbel. The health index is a version of the consumer price index that excludes products such as alcohol, tobacco and motor fuel, so it tends to rise a little more slowly than headline inflation.

Crucially, indexation is not a rent increase the landlord invents — it is a legally defined recalculation. A landlord cannot raise the rent by a freely chosen amount "because the market went up." They can only apply the indexation formula below.

How much can the rent go up? The formula

The legal formula for indexing residential rent in Belgium is:

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

• The base rent is the rent agreed in the lease (before any earlier indexation).
• The starting index is the health index of the month before the lease was signed.
• The new index is the health index of the month before the lease's anniversary date.

Worked example. Suppose the base rent is €1,000, the starting index was 120.00 and the new index is 124.80. The indexed rent is:

€1,000 × (124.80 ÷ 120.00) = €1,040.00 — a €40 (4%) increase.

Because the index changes every month, the only way to get the exact figure for your lease is to use the current published health index. Our free rent-indexation calculator fills in the official index automatically and shows the formula, the percentage and a ready-to-send letter. (French-speaking? Use the calcul d'indexation du loyer.)

When can the rent be indexed?

• Once per year, on the lease anniversary — the date the lease took effect, not 1 January.
• It is not automatic. The landlord must actively request it, in writing. If they forget, the rent stays the same — many landlords quietly lose income this way.
• Limited backdating. A landlord can generally only claim indexation up to about 3 months retroactively; wait longer and the right to those past months is lost.
• The lease must be registered, and depending on your region and the property's energy performance certificate (EPC/PEB), the indexation may be reduced or capped. These energy-based conditions differ across Flanders, Brussels and Wallonia and have changed in recent years — check the current rule for your region before applying an increase.

Is my rent increase legal? (for tenants)

If you have just received an indexation notice, check it in three steps:

• Timing: is it on or near your lease anniversary, and not more than ~3 months late?
• The maths: run your base rent and dates through the calculator. If the landlord's figure is higher than the formula gives, it is not correct.
• The index: it must be the health index — not headline inflation or a round-number "market" increase.

Indexation that follows the formula is a legal right of the landlord and cannot simply be refused. But an increase that ignores the formula, the timing, or a regional EPC cap can be challenged — start by asking your landlord, in writing, to show the calculation.

Never miss (or miscalculate) an indexation again

ImmoDesk tracks every lease's anniversary, fetches the official Statbel health index, calculates the correct indexed rent, and generates a legally compliant indexation letter in Dutch or French — so landlords never lose income to a forgotten indexation, and never overcharge by accident. 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.