In short: during a running lease you can't simply raise the rent. There are only two routes: the yearly indexation, and a rent revision at the end of each three-year period, for example if your works raised the rental value by at least 10%. With a new tenant and a new lease, you set the rent again, in principle freely; in Brussels, within the limit of a non-excessive rent.

Three situations that often get mixed up

During the lease: indexation isn't an increase

Indexation adjusts the rent once a year to the health index, on the anniversary of the lease's start. It isn't a free increase and can't be used to pass on renovation costs. How to calculate it: How to Calculate Rent Indexation in Belgium (2026).

The rent revision: the only route after works

In a nine-year lease, landlord and tenant can ask for a rent revision at the end of each three-year period. It has to be requested in a specific window: between the ninth and the sixth month before the end of that period.

• By agreement, you can set a new rent together. Put it in writing.
• Without agreement, the justice of the peace can revise the rent, but only if the normal rental value:
  • is at least 20% higher or lower than the current rent because of new circumstances, or
  • has risen by at least 10% through works at your expense. Ordinary maintenance and repairs don't count.

The judge decides fairly and may, for example, take normal depreciation of the works into account. A revision can also lead to a lower rent if the rental value has fallen.

In practice: renovating during the lease

1. Agree the works in advance with the tenant, and whether and how they affect the rent.
2. Keep invoices and before-and-after photos: they're your proof of the higher rental value.
3. Note the revision window: between nine and six months before the end of the current three-year period.
4. Request the revision in writing, preferably by registered letter, with a concrete amount.

A new tenant: a new rent

If the tenant leaves and you sign a new lease with a new tenant, you set the rent again. In Flanders and Wallonia it's in principle free; the indicative rent tools aren't binding. In Brussels, since May 2025, the rent may not be excessive compared with the reference grid.

Careful: signing a new lease with the same tenant just to raise the rent doesn't work that simply. A nine-year lease keeps running, and a series of short-term leases can turn into a nine-year lease on the original terms. See How Long Is a Belgian Residential Lease?

What about energy performance?

With renovations, also think of the EPC: in Flanders and Wallonia, a poor EPC can limit the indexation you're allowed to apply. Energy works improve the rental value and can also restore full indexation.

The right rent, at the right time

ImmoDesk keeps the rent and every change for each lease. On the lease anniversary it calculates the indexation with the health index and prepares the indexation letter; you approve it before it's applied. Try ImmoDesk free for 7 days, no credit card required.

This article is general information about rent adjustments under residential leases in Belgium, valid in 2026, and is not legal advice. The rules differ by region (Flanders, Brussels, Wallonia) and change over time. Check your situation with a lawyer or a landlords' association.