The IM index is an update of the value of property in the absence of an available replacement value in the calculation of the equipment charges, apprehended from 7 positions in a cost accounting approach : "labour costs" once called "salaries and expenses", "materials" , "material", "energy", "transport", "miscellaneous expenses", similar to the productivity economists' approach called "KLEMS"(K = capital for "equipment", L = "Labour" ," E = "energy", M = "materials", S = "Services" for miscellaneous expenses) and which are added the positions T (= transport) for "transport" and D (= déchets) for "wastes". Each position is it-self treated from elementary indices.

The structure and weights of the IM index have been reviewed on the occasion of the change in base and reference 2010.

Weights are constructed following, in particular, structural sources Insee and the work carried out with professional unions which rely on building site data returns.

IM index is chained Laspeyres indice of elementary indices from public statistics, in particular the all employees-revised index of hourly labour cost (ICHTrev-TS) and the Industrial Producer and Import Price Indices (IPPI)