The quarterly commercial rent index (ILC) created by Law n°2008-776 of 4 August 2008 on modernisation of the economy, is composed of indices representing trends in :
- consumer prices ;
- new construction prices ;
- retail trade sales.
The index representing trends in consumer prices is the INSEE consumer price index, excluding tobacco and housing rents, for households in Metropolitan France and the overseas departments (IPCL). New construction prices are taken into account by the INSEE cost-of-construction index (ICC). Retail sales trends, meanwhile, are represented by the monthly retail sales index. This is published by INSEE, expressed in value and corrected for seasonal variations and working days (ICAVaCD).
Each of the indices composing the ILC is calculated as a mean :
- over 12 consecutive months for consumer prices and sales, which are monthly indices (mIPC and mICAVaCD) ;
- over 4 consecutive quarters for the cost of construction index which is quarterly (mICC). To calculate these means, the last month (or quarter) taken into consideration corresponds to the last month of the quarter (or to the quarter) for which the ILC is being calculated. Each of the means calculated in this way and the ILC itself are expressed in relation to a reference of 100 in the first quarter of 2008.
The three indices contribute to the calculation of the ILC according to the following weighting: Quarterly commercial rent index (ILC) = 50% mIPCL + 25% mICC + 25% mICAVaCD.
Decree n°2008-1139 of 4 November 2008 relating to the quarterly national commercial rent index defines the terms of calculation and publication of this index, as well as the activities concerned.
According to the Law 2014-626 of June 18th, 2014 (article 9) which modifies it, and the article L145-34 of the commercial law by resulting, two indicators can be used for the revision of the professional leases: the commercial rents index and the tertiary activities rent index.