Rent indexation is one of the most important — and most forgotten — tasks for a landlord. Apply it correctly and you protect your rental income against inflation. Forget it, and you quickly leave hundreds of euros on the table each year. This guide explains how to calculate rent indexation correctly in 2026.
What is rent indexation?
Rent indexation is the annual adjustment of the rent to the cost of living, based on the health index (gezondheidsindex). The health index is a derivative of the consumer price index that excludes products such as alcohol, tobacco and fuel.
When can you index?
- At most once per year.
- At the earliest on the anniversary of the lease entering into force.
- Only if indexation was not excluded in the lease.
Important: for residential leases, indexation is not automatic. As a landlord you must notify your tenant in writing. You can backdate the indexation by a maximum of three months from the moment of your written request.
The formula
The calculation is simpler than it looks:
New rent = Base rent × (new health index / starting index)
The starting index is the health index of the month preceding the month the lease was signed. The new index is the health index of the month preceding the month of the lease anniversary.
Worked example
Suppose a lease started on 1 May with a base rent of €900. To index on the 2026 anniversary you need two index figures:
- The starting index: the health index of the month before signing.
- The new index: the health index of April 2026 (the month before the May anniversary).
- Then apply the formula: New rent = €900 × (new index / starting index).
You can find the exact index figures on the official Statbel rent calculator.
Mind the EPC restriction
Since 1 October 2023, indexation in Flanders is restricted for properties with an EPC label of D, E or F, with the strictest limits applying to the worst labels. Always check your property’s energy label before indexing. For leases signed before 1 October 2022, a correction factor also applies.
Never miss an indexation again
The biggest pitfall is not the calculation — it is forgetting. A missed indexation can cost you €500 or more per property per year, money you cannot fully recover retroactively. Proproll calculates the correct indexation automatically for every property, accounts for the EPC label, and reminds you in time for each anniversary.
This guide is general information and not legal advice. Always check the current index figures on statbel.fgov.be and consult a property expert when in doubt.