HICPs across Member States aim to be comparable. Any differences at all levels of detail should only reflect differences in price changes or expenditure patterns.

To this end, concepts and methods have been harmonised by means of legislation. HICPs that deviate from these concepts and methods are deemed comparable if they result in an index that is estimated to differ systematically by less than or equal to 0.1 percentage points on average over one year against the previous year (Article 4 of Council and Parliament Regulation (EU) 2016/792).

HICP data are fully comparable over time. There have been several improvements in methodology since HICP was introduced with the aim of improving reliability and comparability of the HICP. These changes may have introduced breaks in time series. However back calculations under the newer standards were performed when appropriate basic data was available.

The CPI and HICP classification is consistent with the 5-digit ECOICOP classification. Around the 15 of each month m+1, to coincide with the publication of the definitive CPI and HICP, other complementary indicators are published: overall index corrected for seasonal variations, index excluding public tariffs and products with volatile prices corrected for tax measures (core inflation), and index for the large retail sector. Indices which are representative of the different household categories are also published (at a monthly or annual rate according to the household category). All of these indices are consistent with the HICP.