The Consumer Price Index, which is a Laspeyres-type index, is based on a fixed basket of goods and services  whose prices are tracked each month. This basket is updated each year to take into account changes in household consumption. The index is then chain-linked annually during the month of January to update the basket, review the weights associated with each product and introduce a number of methodological improvements.

Consumption items are described according to the European Classification of Individual Consumption by Purpose, 2nd version (eCOICOPv2). It is linked to the international COICOP 2018 nomenclature and supplemented by a 5th level developed by Insee, referred to as 'postes' (expenditure items).