Rent indexation

How StoffRent calculates the indexed rent, and the steps from “due” to “applied”.

How the new rent is calculated

For a Belgian lease, the indexed rent is the rent in the contract multiplied by the health index of the month before the anniversary, divided by the base index:

new rent = contract rent × index of the month before the anniversary ÷ base index

  • The contract rent is always the original one, never last year’s indexed rent: there is no snowball effect.
  • The base index is the one of the month before the lease was signed, unless the contract states another one - you can enter it on the lease.
  • The anniversary follows the lease’s start date.
  • Charges are not indexed.
  • The index series follows the signature year: the 2013 base for leases signed before 2026, the 2025 base for leases signed from 2026.

From due to applied

Every lease gets its anniversaries on the Indexations page. Each one goes through the same steps:

  • Upcoming: the anniversary is ahead.
  • Due: the anniversary has come; the index needed is (or soon will be) published.
  • Calculated: StoffRent has computed the new rent - check it.
  • Letter sent: you have sent the letter to the tenant.
  • Applied: the new rent is the lease’s current rent from the anniversary on.
  • Skipped: you decided not to index this year. Skipping one year does not lose it: the next calculation still starts from the contract rent.

The indexation letter

Once an indexation is calculated, download the letter: a PDF in the lease’s language with the formula, the index values and the new rent, ready to send. Mark it as sent with the date you sent it.

Energy certificate and warnings

Some regions limit or forbid indexation depending on the energy certificate. When a rule applies, or when an index value is missing or not verified, StoffRent shows a warning next to the amount, before you send anything. The warnings cannot be dismissed: read them, and check the amount against the rules that apply to your lease.

Your own index series

If a lease follows an index StoffRent does not publish, create your own series in Settings → Index series and enter its values by hand or import them from a CSV file (period;value). Leases can then use it like any official series.