He can only do this once a year, in writing and at the earliest on the anniversary of the start of the lease and he can go back three months at most. 

There are only two rules where indexation may not be applied:

- When your lease expressly states that indexation is not allowed.

- When you concluded an oral lease after 30 May 1997 and the landlord cannot prove that this was agreed.

The Flemish government froze the rents of the most energy-hungry houses for 1 year: from 1 October 2022 to 30 September 2023. The ban on indexation of rents applies to all current housing leases. In other words, these are rental agreements concluded before 1 October 2022 under the Housing Rental Act or the Flemish Housing Decree.

In concrete terms, this means:

- The EPC must be valid. An EPC has a maximum validity period of 10 years. 

EPCs issued before 1 October 2012 are no longer valid. An EPC that was still valid at the time the lease was signed but has since expired is also no longer eligible.

- Indexation is not allowed for houses with an EPC label E or F or for houses without an EPC certificate.

- For houses with an EPC label D, the indexation is limited to 50%. 

The landlord calculates the difference between the current rent and the indexed rent (calculated using the standard indexation formula) and divides this amount by two. The landlord then adds this divided amount to the current rent.

- For energy-efficient houses with an EPC label A+, A, B or C, nothing changes. Landlords of those homes are still allowed to index the rent.

From 1 October 2023, indexation for rental homes without an EPC or with a label D, E and F will again be allowed, but according to a modified formula. This way, tenants will not suddenly get a very high rent after 1 year.