Indexation of commercial leases in Belgium

Answer in brief

The indexation of a commercial lease in Belgium falls under a legal regime distinct from residential. Unlike the residential lease where indexation is a right (subject to registration), commercial lease indexation Belgium strictly depends on an explicit contractual clause in the lease. Without a clause, no indexation. With a clause, the health index remains the default reference.

The legal framework: Law of 30 April 1951

The regime of the Belgian commercial lease is governed by the Law of 30 April 1951 on commercial leases, still in force (modified several times but never repealed). This federal law frames property rentals intended for the exercise of a retail trade or a craft activity in direct contact with the clientele.

Main characteristics:

• Minimum duration of 9 years (article 3)
• Triennial renewal possible: the tenant can request renewal under the conditions set by the law (articles 13 to 22)
• Triennial rent revision provided in article 6 (distinct from indexation, see below)
• Scope: shops, workshops, restaurants, hair salons, etc.

⚠️ Important exclusions: liberal professions (lawyers, doctors, architects…) fall under another regime — the common law lease of the Civil Code. Pure offices without client contact may also escape the 1951 law depending on the circumstances.

Indexation: contractual clause rather than law

This is the key point of any commercial lease indexation Belgium: unlike residential, the 1951 law does not provide for automatic indexation. The mechanism of annual adaptation of the commercial rent rests entirely on contractual freedom.

Three practical consequences:

1. The commercial lease must explicitly provide for indexation for it to be due
2. Without an indexation clause, the rent stays frozen during the 9 years of the lease (except triennial revision, which follows a different logic — see dedicated section)
3. If the clause is vague or ambiguous, the settled case law of the Court of Cassation interprets it in favour of the tenant (the commercial tenant). A poorly drafted clause can be declared non-opposable

This contractual autonomy is both an opportunity and a risk. Opportunity, because the parties can freely negotiate the formula, the reference index and the periodicity. Risk, because an approximate drafting can deprive the landlord of their indexation right during the entire duration of the lease.

The health index remains the reference (except contrary clause)

When a commercial lease provides for an indexation clause without specifying the reference index, the constant practice since the Law of 6 August 1993 is to use the health index. This is also what the courts retain in case of dispute on the applicable index.

The health index is calculated each month by Statbel and excludes products like tobacco, alcohol and fuel. It is the same index as the one used for residential — which simplifies the practice for landlords with mixed portfolios.

Theoretically, a commercial lease can provide for another index:

• Consumer price index (CPI)
• Specific sector index
• Mixed formula (e.g. weighted average of indexes)

In practice, these alternative clauses are rare and present an increased risk of dispute. The health index remains the safe value for the majority of commercial lease indexations in Belgium.

Periodicity: annual or triennial?

A frequent confusion concerns the periodicity of the commercial rent adaptation. Two mechanisms coexist and it is essential not to confuse them:

Annual indexation (contractual clause)

If the lease provides for an indexation clause, it generally applies each year on the lease’s anniversary date, according to the contractual formula. It is the equivalent of residential indexation, but of contractual and not legal origin.

Triennial revision (article 6 of the 1951 Law)

At each triennial term of the commercial lease (end of the 3rd, 6th or 9th year), the landlord or the tenant can request a rent revision if they demonstrate that the rental value has varied by at least 15 % compared to the indexed rent.

This procedure is distinct from indexation:

• Indexation follows a mathematical formula (health index)
• Triennial revision is based on the property’s actual rental value and generally requires a judicial expertise in case of disagreement
• Both can coexist: a lease can be indexed each year and revised every 3 years

Differences with the residential lease

The table below summarises the main differences between residential and commercial lease in terms of indexation and general framework:

Criterion	Residential	Commercial
Main legal framework	Law of 6 August 1993 + regions	Law of 30 April 1951 (federal)
Indexation	A right (if lease registered)	Mandatory contractual clause
Reference index	Health index (imposed)	Health index by default, free by contract
EPC coefficient	Yes (Brussels, Wallonia since 2022-2023)	No, never
Minimum duration	Variable (3, 6 or 9 years depending on type)	9 years (mandatory)
Triennial rent revision	Not provided	Yes (article 6 of 1951 Law)
Renewal	Tacit or simple notification	Formal procedure (art. 13-22 of 1951 Law)
Registration	Mandatory (landlord’s responsibility)	Mandatory (tenant’s responsibility)

This differentiation explains why the same owner can hold two properties leased under radically different regimes — hence the importance of checking the nature of the lease before any indexation action.

Special case: Wallonia / Brussels / Flanders

For residential, the three Belgian regions have adopted their own rules since 2018 (EPC coefficients, temporary capping, reinforced registration requirements). In commercial lease matters, the landscape is much simpler:

• The federal Law of 30 April 1951 applies uniformly throughout the territory
• The recent Brussels ordinances and Walloon decrees (2022-2023) on indexation linked to EPC only concern residential
• No EPC coefficient applies to commercial leases, in any region
• Flanders also has no specific regional regime for commercial

In practice, commercial lease indexation Belgium therefore follows the same rules in Liège, Brussels or Antwerp — subject, of course, to the language and the competent court. This uniformity simplifies management for multi-regional commercial portfolios.

How to calculate a commercial indexation

If your commercial lease provides for an indexation clause based on the health index (majority case), the applicable formula is identical to the residential one:

Indexed rent = Base rent × (New index ÷ Base index)

With:

• Base index: health index of the month preceding the lease signature (or the stipulated contractual base — 1996, 2004, 2013)
• New index: health index of the month preceding the adaptation anniversary date

Our indexation calculator applies this formula. Be careful: the contractual clause may specify an index base different from the standard (for example, base 2013 = 100). One must then strictly respect the base provided in the contract and use the indexes converted in the same base. Our methodology page details the conversions between health index bases.

Concrete example: Brussels retail business

Take a retail business in Brussels, lease signed on 1 September 2018 for the amount of €2,400 excl. VAT/month, with an annual indexation clause based on the health index.

In September 2026, the landlord applies the annual indexation:

• Base index = August 2018: 107.07
• New index = August 2026: 132.69
• Calculation: 2,400 × (132.69 ÷ 107.07) = €2,974.16 excl. VAT/month

The increase is €574.16/month, that is 23.9 % over 8 years, which reflects the cumulated inflation measured by the health index over this period. To automate this calculation:

Frequent errors

Three recurring pitfalls in commercial lease indexation Belgium:

1. Confuse indexation and triennial revision. Annual indexation is an automatic mathematical formula (if clause). Triennial revision (art. 6) is a distinct procedure based on the rental value and limited to triennial terms. Both can accumulate but do not substitute each other
2. Index a commercial lease without an explicit clause. No legal basis allows automatic indexation in commercial. If the lease is silent, the tenant has the absolute right to refuse. Our when to index guide details the general applicable conditions
3. Apply a regional EPC coefficient. The EPC modulations introduced by the regions in 2022-2023 only concern residential. Any attempt to modulate commercial indexation according to the energy class is legally unfounded and disputable before the justice of the peace

A fourth, more subtle error: forget that civil prescription also applies to commercial. If an annual indexation provided by the lease is not claimed, it follows the same prescription rule as residential — see our guide on forgotten indexation.

Going further

• How to calculate an indexation step-by-step
• When can a rent be indexed?
• What to do after several years without indexation?
• Complete calculation methodology
• Indexation calculator

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This article is informative and does not constitute legal advice. For high-stake commercial leases, consultation of a lawyer specialised in real estate law is recommended. Main sources: Law of 30 April 1951 on commercial leases (notably art. 6 and art. 13-22), Law of 6 August 1993 on lease contracts, article 1728^bis of the Belgian Civil Code, settled case law of the Court of Cassation on the interpretation of contractual clauses.