The indexation notice can be sent:
- Earliest: on the anniversary of the lease’s entry into force
- Effect: the indexed rent is due from the month following the written request
- Retroactivity: maximum 3 months back (from the written request)
Example: lease entered into force on 1 March 2024. You can request indexation from 1 March 2025. If you send the letter on 15 April 2025, the new rent is due from May 2025, with the possibility to claim the difference for March and April.
The legal indexation formula is:
Base rent x New index / Starting index = Indexed rent
| Element | Definition |
|---|---|
| Base rent | Initial rent stated in the lease |
| New index | Health index of the month preceding the anniversary |
| Starting index | Health index of the month preceding the lease signing |
Our generator automatically performs this calculation using your lease data.
The document includes:
- Identification of landlord and tenant
- Reference to the lease (date, address)
- Reminder of the base rent
- Calculation detail (indices used, formula)
- New indexed rent amount
- Effective date
- Reference to the applicable legal article
The notification can be sent by:
- Ordinary mail: legally sufficient
- Email: accepted if the lease provides for electronic communication
- Registered mail: recommended for difficult tenants
- Via the platform: automatic notification through LeaseBelgium’s tenant portal
Keep proof of sending (dated copy, email read receipt, or postal tracking).