Commercial Rent Review Simulator and the 2026 ILC: Complete Guide

Are you the owner or tenant of commercial premises and wondering how your rent will change? Revising a commercial rent by reference to the commercial rent index (indice des loyers commerciaux, ILC) is a major financial issue and calls for a methodical approach. Understanding how a commercial rent review simulator works and mastering the calculations for the 2026 ILC will allow you to anticipate your obligations and protect your interests.

What is the commercial rent index (ILC)?

Definition and role of the ILC

The commercial rent index is the reference tool for revising rents under commercial leases in France. Published quarterly by INSEE (the French national statistics institute), it reflects changes in the cost of living and in economic activity. It applies specifically to leases entered into or renewed since 1 September 2014, and has gradually replaced the construction cost index (ICC) in many contracts.

The ILC is made up of three main components, which represent the costs borne by commercial businesses:

• The consumer price index (50%)
• The construction cost index (25%)
• The retail turnover index (25%)

Recent changes in the ILC

2024 was a period of high volatility for the ILC, mainly because of inflationary pressure. That trend continues in 2026, which makes a commercial rent review simulator all the more useful for anticipating variations. Owners and tenants alike should monitor these developments closely in order to plan their budgets.

The legal framework for commercial rent reviews

The provisions of the French Commercial Code

Commercial rent reviews are governed by a strict legal framework set out in the French Commercial Code. Articles L145-37 et seq. regulate the review procedure, the time limits and the conditions of application. The lease must provide for a review clause before a review can be carried out. The various mechanisms for increasing rent, from automatic indexation to renewal, are set out in our article on rent increases under a commercial lease.

A review can take place in two ways:

• A contractual review provided for in the lease (generally every 3 years)
• A statutory review requested by one of the parties

Conditions of application

Several conditions must be met for a review to be valid. The lease must contain an express indexation clause stating the reference index. The review request must comply with the form and time limits prescribed by law. Where the contract contains no such clause, a statutory review remains possible but on more restrictive terms.

How a commercial rent review simulator works

Basic calculation principle

A commercial rent review simulator automates the complex calculation of the new rental value. The principle remains simple: the new rent equals the initial rent multiplied by the ratio between the current ILC and the reference ILC.

The basic formula is: New rent = Initial rent × (current ILC / reference ILC)

Data required for the calculation

To use a simulator effectively, you need to gather several key items of information:

• The amount of the base rent at the time it was set or last revised
• The reference date for the index (generally the date the lease was signed or last revised)
• The ILC figure corresponding to that reference date
• The most recent ILC figure published by INSEE

Types of simulator available

The market offers different types of tool for calculating commercial rent. Free online simulators provide a first approach, but their accuracy may be limited. Professional software incorporates the latest regulatory developments and offers advanced functions. Law firms that focus on this area sometimes develop their own tools suited to their practice.

Detailed calculation for the 2026 ILC

Step-by-step calculation method

To carry out an accurate calculation with the 2026 ILC, follow this structured approach:

Step one: identify the reference index stated in your lease or corresponding to the date of the last review. This information is generally found in the contract's indexation clause.

Step two: consult INSEE's official publications to find the applicable 2026 ILC. The index published for the relevant quarter is the one to use in the calculation.

Step three: apply the calculation formula, checking that the dates and indices used are consistent.

Worked example

Let us take a concrete example to illustrate the use of the 2026 ILC. A commercial lease signed in 2023 provides for an initial rent of €2,400 per month, with a reference ILC of 115.8 points (2nd quarter 2023). If the 2026 ILC for the 1st quarter reaches 122.4 points, the calculation is:

New rent = 2,400 × (122.4 / 115.8) = 2,400 × 1.057 = €2,537

This increase of €137 per month represents a rise of 5.7%, which illustrates the significant effect of changes in the index.

Particular features of the 2026 calculation

The 2026 ILC has certain features linked to the current economic context. The effects of inflation on the "consumer prices" component continue to influence the index. Monetary policy and geopolitical tensions also affect construction costs. These factors make a commercial rent review simulator particularly relevant for anticipating variations.

Special cases and exceptions

Differential review

Some leases provide for differential review mechanisms, under which the increase may not exceed a certain annual percentage. In that case, the simulator must take this contractual limit into account in order to give an accurate result.

Capping of increases

The law provides mechanisms to protect against excessive variations. Where the index changes exceptionally, specific rules may apply. In certain circumstances, the tenant may ask for the increase to be spread over several years.

Derogatory leases

Short-term leases (under 3 years) and leases derogating from the commercial lease statute (baux dérogatoires) may follow different rules. The indexation clause must be analysed carefully to determine which index applies.

Common errors to avoid

Confusion between indices

A frequent error is to confuse the ILC with the ICC (construction cost index) or the IRL (reference rent index). Each index has its own specific field of application. Always check that your lease does refer to the ILC before using a commercial rent review simulator. The choice of the applicable index under the lease since the Pinel Act is explained in our guide to the construction cost index.

Date errors

The reference date of the index must match exactly the date provided for in the lease. An error of one quarter can significantly distort the calculation. Keep all documents relating to previous reviews carefully.

Neglecting time limits

A review request must comply with strict time limits. A delay can cause the right to a review to be lost or its effects to be postponed. Plan your steps ahead by using a calendar to track deadlines. The point from which the request may be made is explained in our step-by-step guide to the three-yearly review of commercial rent.

Practical implications for owners and tenants

For owners

Mastering the calculation of commercial rent makes it possible to optimise the return on your property portfolio. Monitor changes in the ILC regularly and schedule your review requests at the right time. A simulator can help you assess the financial impact before starting a procedure.

For tenants

Understanding the review mechanism allows you to budget accurately for your rental costs. You can also check the validity of review requests made by your landlord and challenge any calculation errors.

Negotiation and mediation

Transparent calculations make negotiation between the parties easier. A simulator can serve as an objective basis for discussion and reduce disputes. Where disagreement persists, mediation remains a worthwhile alternative to litigation.

Regulatory developments and outlook

Ongoing reforms

The legislature regularly adapts the legal framework for commercial leases to economic change. Recent reforms aim to balance landlord and tenant relations and to protect businesses in difficulty. Follow the official publications to stay informed of changes.

Impact of digitalisation

Digital tools are transforming the management of commercial leases. Online simulators are improving and incorporating advanced functions. Artificial intelligence may soon allow more accurate forecasts of how indices will move.

Advice on choosing a simulator

Selection criteria

A good commercial rent review simulator should offer several guarantees:

• Automatic updating of the official indices
• An intuitive interface and clear results
• Handling of special cases
• Traceability of the calculations carried out
• Technical support in case of difficulty

Validating the results

Whatever tool is used, always check that your results are consistent. Compare them with manual calculations on simple examples. If in doubt, do not hesitate to consult a property law professional.

Mastering the tools used to calculate commercial rent reviews is a strategic matter for everyone involved in commercial property. A reliable commercial rent review simulator, combined with a good understanding of the 2026 ILC, will allow you to make informed decisions and secure your contractual relationships. Given the growing complexity of the regulations and the considerable financial stakes, the support of a French lawyer who focuses on property law remains the best guarantee for protecting your interests and optimising your asset strategy.