Everything you need to know about commercial lease indexation: current figures for 2026, calculation formulas, retroactive indexation, and practical examples. Advice from attorneys specializing in commercial leases.
Table of contents
- Introduction: commercial lease and indexation
- Legal framework for commercial lease indexation
- Indexing mechanisms and calculation
- Practical aspects of indexation
- Special indexation situations
- Frequently asked questions (FAQ)
Introduction: commercial lease and indexation
What is indexation and why is it important in commercial leases?
Indexation of commercial lease is a mechanism that allows the adjustment of the rent to the evolution of longevity. It is an essential component of long-term commercial leases, which, according to the Commercial Lease Law have a minimum duration of nine years.
Commercial lease indexing protects your income as a landlord from currency depreciation and inflation. For tenants, it means predictable, gradual rent adjustments rather than sudden, large increases.
Indexation commercial lease is not a revision of the rent, but rather a method of pricing where a variable fee is negotiated instead of a fixed amount. It is an automatic mechanism that protects the parties from economic fluctuations over the long term of the agreement.
Legal basis for indexation
The ability to index commercial lease finds its legal basis in article 1728bis of the old Civil Code. No article in the Commercial Lease Law opposes an indexation clause. The rent indexation commercial lease is considered a method of rent determination, not a modification of the contract.
Including an indexation clause in a commercial lease is not mandatory but is strongly recommended. Parties remain free to negotiate a fixed rent that remains unchanged throughout the lease term.
Difference between indexation and rent review
It is important to make a clear distinction between indexation trade rent and rent review:
- Indexation automatically adjusts the rent to life expectancy according to a predetermined formula, usually annually.
- Rent review (Section 6 Commercial Lease Law) is an independent claim that can be brought every three years when new circumstances have changed the normal rental value by at least 15%.
An indexation clause does not prevent the possibility of triennial rent review. Both mechanisms can coexist.
The different indexes explained
For the indexation of commercial leases the health index has been used since February 1, 1994. Before this date, the consumer price index was used.
The health index is a derivative of the consumer price index, but without taking into account the price evolution of alcoholic beverages, tobacco products and motor fuels.
The evolution of these indices is published monthly by the FPS Economy and determines the calculation of your index adjustment commercial lease.
Legal framework for commercial lease indexation
Legal basis for indexation
The legal basis for the indexation commercial lease is in article 1728bis of the old Civil Code.
The regulation provides a mandatory formula for calculating the indexed rent when the parties have chosen in their agreement to adjust to the index. This provision applies to all leases, including commercial leases.
Differences between ordinary rent indexation and commercial lease indexation
The rules for commercial lease indexation broadly follow the same principles as for other leases, but there are some specifics:
- With trade leases, parties have more contractual freedom to choose reference points other than the health index.
- They are free to determine the frequency of adjustment, although the legal limitation of no more than one indexation per year continues to apply.
- For mixed premises (both commercial and residential), it is appropriate to negotiate a split rent for tax purposes.
What if the contract does not contain an indexation clause?
If the parties forget to include an indexation clause in the commercial lease, this cannot be rectified until the renewal of the lease after nine years. There is no legal option to add an indexation clause during the term of the agreement unless both parties expressly agree to it through an addendum.
An indexation clause cannot be inserted by the court in the lease following any triennial review under Section 6 of the Commercial Lease Law
Indexing mechanisms and calculation
The indexing formula explained
The legal formula for commercial lease indexation is as follows:
Indexed rent = Base rent × New index figure / Starting index figureThis formula is mandated by article 1728bis of the Civil Code and may not be changed to the detriment of the tenant.
- Base rent: the rent determined when the contract was concluded, renewed or revised.
- Start index: the index figure of the month preceding the month in which the agreement was concluded, renewed or revised.
- New index: the index figure of the month preceding that of the anniversary of the effective date of the lease.
Current index figures for 2026
For correct indexation of commercial leases in 2026, use the current health index figures published by the FPS Economy (Statbel). You can always consult the most recent figures at official website of Statbel.
According to Statbel's most recent publication, the evolution of the health index (base 2013 = 100) is as follows:
- 2021: ranging from 110.35 (January) to 115.60 (December)
- 2022: ranging from 118.21 (January) to 127.89 (December)
- 2023: ranging from 126.70 (April) to 129.53 (December)
- 2024: ranging from 130.19 (January) to 133.73 (December)
- 2025: ranging from 135.52 (January) to 136.69 (December)
These index figures are updated monthly and are essential for correctly calculating your commercial lease indexation for 2025 and commercial lease indexation for 2026.
Step-by-step indexation calculation
To correctly perform the index commercial lease calculation, follow these steps:
- Determine the base rent: This is the originally agreed rent without costs and charges.
- Find the starting index number: This is the index figure for the month prior to the conclusion of the lease.
- Find the new index number: This is the index figure for the month before the anniversary of the effective date of the lease.
- Apply the formula: Base rent × New index figure / Starting index figure
Example: A commercial lease agreement concluded on December 15, 2019, with a base rent of €1,500 per month and effective January 1, 2020.
- We look up the initial index figure: this is the index figure for the month before the agreement was concluded (November 2019). According to Statbel's official table, this is 109 (base 2013 = 100).
- For the indexation in 2026, we need the new index figure for the month before the anniversary of the entry into force (December 2025). According to the official figures from Statbel, the health index for December 2025 is 136.69.
- We apply the legal formula: Indexed rent = €1,500 × 136.69 / 109 = €1,500 × 1.2540 = €1,881.06
The indexed rent will therefore be €1,881.06 per month from January 2026.
Note that even small differences in index figures can lead to noticeable differences in the indexed rent. This shows why it is so important to always use the exact correct index figures in these calculations.
Maximum indexation and limitations
Pursuant to Article 1728bis of the Civil Code, there is a legal limit on the indexation of commercial leases. The indexed rent may never exceed the amount obtained by applying the statutory indexation formula.
Moreover, it stipulates that the index adjustment should be done only once a year. Any clause providing for more frequent adjustments is against the law.
Conversely, index clauses that are more favorable to the tenant than the statutory regulation (for example, indexing every two or three years instead of annually) remain valid.
Practical aspects of indexation
When to index?
In principle, the indexation trade rent occurs annually, on the anniversary of the effective date of the lease. The adjustment does not take effect automatically, unless the agreement expressly states that the indexation occurs "by operation of law" or "automatically."
In practice, this means that the landlord mustcommercial lease. It is advisable to set up a system of reminders to avoid forgetting to request indexations.
Procedure for correct indexing
For a correct index adjustment commercial lease, follow this procedure:
- Check if your lease contains an indexation clause: Without this clause, indexing is not possible.
- Calculate the new rent: Use the legal formula and current indices.
- Inform the tenant: Send timely written notification with the detailed calculation.
- Document the process: Keep copies of all communications and calculations.
Preparation of an indexation letter
A proper indexation letter for commercial lease indexation contains at least the following elements:
- Identification of the leased premises
- Reference to the indexation clause in the lease
- Clear statement of base rent
- The starting index number and the new index number
- The detailed calculation of the new rent
- The effective date of the indexed rent
- Payment Instructions
The letter should be sent in a timely manner, ideally one month before the anniversary of the effective date of the lease.
What if the tenant does not agree?
If the tenant does not agree to the indexation trade rent, there are several options:
- Consultation: An amicable conversation can clear up misunderstandings.
- Control calculation: Have the calculation checked by an independent third party, such as an accountant or real estate expert.
- Legal advice: Consult an attorney specializing in commercial leases.
- Judicial proceedings: As a last resort, a claim can be filed with the justice of the peace.
In practice, disputes usually arise from miscalculations or discussions about the applicability of the indexation clause, not about the principle of indexing commercial lease itself.
Special indexation situations
Retroactive indexation
One of the most frequently asked questions concerns the possibility of retroactive indexation of commercial rents. The law provides for a limitation period of one year for the indexation of rents (commercial lease and common lease), in accordance with Article 2273 of the old Civil Code.
In practice, this means that a landlord who has forgotten to index the rent can do so retroactively for a maximum of one year. However, it is important to note that receiving a non-indexed rent does not imply a waiver of the right to indexation.
Retroactive indexation of commercial leases requires careful calculation using the correct indices for each year.
Indexation on long-term contracts
For long-term commercial leases, consistent application of the indexation commercial lease is essential to prevent depreciation. Indeed, over a nine-year period (the minimum term of a commercial lease), inflation can have a significant impact on the fair value of the rent.
Successive indexations should always be based on the original base rent. It is not correct to take the already indexed rent as the new base, as this would lead to an exponential increase (the so-called "snowball effect").
Indexation forgotten or omitted
If, as a landlord, you have forgotten to apply for commercial lease indexation, you have the right to correct this retroactively, within the statutory limitation period of one year.
Defaulting on indexation does not lead to loss of this right. The case law is clear: merely receiving a non-indexed rent without reservation does not count as a renunciation of the right to indexation.
For correct rectification of forgotten indexations, you as a landlord must:
- Accurately calculate missed indexations
- Inform the tenant in writing of the correction
- Propose a reasonable payment plan for the overdue amounts
Indexation on revised or renewed contracts
When a commercial lease is renewed or extended, a new contractual situation arises. For the index trade lease, this means:
- Upon renewal, the new agreed rent becomes the base rent before future indexations.
- The starting index number will be the index number for the month prior to the renewal.
- Any revised rent (through Section 6 Commercial Lease Law) also becomes the new base rent.
It is important to re-evaluate the indexation clause each time the contractual terms are changed and, if necessary, adjust it to the current situation.
Frequently asked questions (FAQ)
How should I index commercial lease?
To index commercial leases, apply the formula: Base rent × New index figure / Initial index figure. First, check if your lease contains an indexation clause and make sure you are using the correct indices.
What index is used for commercial lease?
For commercial leases concluded as of February 1, 1994, the health index shall be used. For contracts prior to this date, the consumer price index shall apply.
Can I retroactively index commercial lease?
Yes, retroactive indexation is possible within the statutory limitation period of one year. However, you must use the correct index figures for each year.
May I index commercial lease without mentioning it in the contract?
No, indexation is possible only if the contract contains an indexation clause. Without this clause, the rent remains unchanged during the term of the contract.
How do I calculate commercial lease indexation correctly?
For a correct calculation, you need: the base rent, the starting index number (month before contract closing) and the new index number (month before anniversary). Then apply the legal formula.
When should commercial lease indexation be requested?
Indexation is usually requested around the anniversary of the effective date of the lease. Some contracts provide for automatic indexation, but usually the landlord must actively request it.
Is indexation of commercial lease mandatory?
No, indexation is not mandatory. It is a contractual option that parties can include in the lease. Without an indexation clause, the rent remains unchanged.
What is the maximum period for retroactive indexation?
The maximum period for retroactive indexation of commercial leases is one year, in accordance with article 2273 of the old Civil Code.
Should I report indexation of commercial lease via registered letter?
The law does not require a registered letter to notify indexation. Nevertheless, it is advisable to communicate indexation in writing and keep proof of mailing.
How frequently may I index commercial lease?
Legally, indexation may only occur once a year. Clauses providing for more frequent adjustments are against the law and therefore invalid.
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