Using the official health index and the legal formula per region, including the Flemish EPC correction factor. Unlimited, no account needed.
How do you calculate the indexed rent of a house, apartment or commercial property? We explain the legal formula with concrete examples.
Indexation follows a fixed legal formula: new rent = base rent x new health index / initial index. The base rent is the amount agreed in the original lease, excluding charges. The initial index is the health index of the month preceding the signing of the lease. The new index is the one for the month preceding the anniversary date. Note: for Flemish residential leases that took effect from 1 January 2019, the reference is the month before the lease took effect rather than the signing month.
The health index is derived from the consumer price index, with tobacco, alcohol, petrol and diesel removed. It is calculated and published monthly by Statbel, the Belgian statistical office, usually towards the end of the month. It is this index, and not the ordinary price index, that serves as the legal basis for rent indexation, so that the adjustment reflects the real cost of living without the effect of excise goods.
Suppose a lease signed in January 2021 with a base rent of 800 euro. The health index for December 2020, the month before signing, was 109.88. In December 2021, the month before the anniversary, it stood at 115.60. The calculation is: 800 x 115.60 / 109.88 = 841.65 euro. From January 2022 your tenant therefore pays 841.65 euro per month, which is 41.65 euro more, or 499.80 euro over the year. Our calculator applies exactly this formula using the official index figures.
Indexation is only possible on the anniversary of the date the lease took effect, which is not always the signing date. If the contract was signed on 15 December 2020 but the tenant only moved in on 1 January 2021, then 1 January is the relevant date. Indexation does not happen by itself: as a landlord you must request it in writing. Without a request the rent stays unchanged, even when all conditions are met.
If you forgot to index you can still do so, but only for a limited period. A written request has retroactive effect for a maximum of three months from the date it is sent. Beyond that the difference is permanently lost, and it repeats every year, because the rent you index from stays lower. With our platform you never miss a deadline again: we track every anniversary automatically.
How do you calculate the indexed rent of a house, apartment or commercial property? We explain the legal formula with concrete examples.
The formula is in principle identical for residential and commercial leases. The contract may however contain specific provisions: a fixed charge that is not indexable, a different indexation date, or a clause limiting indexation. Indexable charges follow the same ratio as the rent, while fixed charges stay unchanged. Our calculator handles both categories separately, for residential leases as well as shops, offices, warehouses and parking spaces.
You can calculate your indexation yourself using Statbel's calculator, or use ours: it is free, requires no account and automatically applies the Flemish EPC correction factor. You immediately see the new rent, the percentage increase and the additional amount over the year. You can also receive a free indexation letter as a PDF, ready to send to your tenant.
In exceptional cases the health index can fall, which would give an indexed rent lower than the previous year. In that case the rent can never drop below the base rent set in the contract, which acts as a floor. In practice the health index has almost always risen over recent decades, so a decrease remains very rare. Our calculator applies this floor automatically.
A rent indexation calculator is more than a simple calculator. The formula itself is straightforward — base rent times the new index divided by the initial index — but the difficulty lies in knowing which figures to enter. Which month serves as the initial index? Does that differ by Region? Does a correction factor apply to your energy certificate? Our calculator answers those questions automatically: you enter the basic details of your lease, we look up the official Statbel index figures and apply the rules of your Region.
Indexing a rent always follows the same order. First you establish your lease's anniversary date: the day it took effect, not the day it was signed. Next you look up the index for the month before that anniversary, along with the initial index that applies to your lease. Then you apply the formula. Finally you send your tenant a written request — without that request the old rent continues to apply, even when every condition is met.
Submit your contract and never miss an indexation.