The ILAT is never included in classic commercial leases, while the ILC remains excluded for certain professional premises. Here, choosing your index is far from a trivial formality: a simple mistake is enough to invalidate the rent revision. The rules are evolving, the update rhythms diverge, and each index applies to a very specific sector. At the crossroads of exceptions, negotiating a real estate contract requires a vigilant eye and a deep understanding of this balancing act.
Why the ILAT and ILC indices have taken precedence in rental contracts
For years, the INSEE construction cost index served as a benchmark in most professional leases. It was imposed without discussion, as an obvious choice in the landscape of rent revisions. Since the Pinel law, it is no longer a matter of selecting the index at will: it must now accurately reflect the activity conducted in the premises. A discrepancy opens the door to disputes and challenges to indexing clauses.
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Before any signature, knowing the nature of each index helps avoid missteps:
- ILC: designed for commerce and crafts, it follows the evolution of household consumption.
- ILAT: reserved for offices, liberal professions, young companies, or consulting firms, it aligns with the tertiary sector.
Their logic is simple: the ILC reflects the climate of daily spending, while the ILAT accompanies tertiary activity and its own inflation. This framework limits deviations: in 2025, the ILAT increase cap at 3.5% will ensure greater stability. As for the ICC, it is no longer valid: using it poses a major legal risk if the contract were to be contested in court.
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ILAT or ILC: distribution according to activity
The choice of index influences everything: the drafting of the revision clause, the calculation methods, the tone of negotiation during renewal. The assignment of one index or the other is never neutral and corresponds to clear categories:
- ILC: businesses, artisans, workshops, salons, or restaurants naturally refer to it.
- ILAT: it is aimed at offices, intellectual professions, service companies, start-ups, or agencies.
A downtown chocolatier will logically see their indexations follow the ILC, true to the fluctuations of local consumption. A consulting firm shifts to the ILAT, which is less volatile, indexed to the dynamics of the tertiary sector. This division preserves contractual equity, as well as the security of both parties. Since 2014, neglecting the coherence of the index exposes the lease to the nullity of its revision clause. Here, the margin for error is almost nonexistent.
Practical calculation: securing your contract step by step
To recalculate a rent, simply apply the formula: current rent × (new index / reference index of the lease). With up-to-date data from INSEE and the right quarter in sight, the rent revision is carried out without unpleasant surprises. This is how the indexing clause retains its strength against scrutiny or contestation.
There are still some old leases indexed to the ICC, mainly for parking lots or small premises. But today, it is with the ILC and especially the ILAT that the majority of professional contracts are aligned. The ILAT frames the increase, offers mutual protection against spikes, and accompanies the changes in the tertiary sector for a smooth adaptation of rents. Both parties, landlord and tenant, benefit from greater predictability, far from the jolts of the past.
Every line counts when drafting the lease: each date, each rate, each type of index must be checked. It is impossible to settle for a copy-paste. In this matter, rigor is the true signature of the contract.
Adopting the right index also helps to pacify relationships: fewer disputes, open discussions, a shared foundation from the start. When each party masters the mechanics of the indices, negotiations proceed without fear of ambiguity or arbitrary decisions. The contract gains in serenity: everyone finds their rhythm, and every adjustment its clarity.