January 2025: annual update of the consumer price index (CPI) with reference year 2013 = 100

The consumer price index (CPI) with reference year 2013 = 100, which was introduced in January 2014, is a chain index that is updated every year in January. The purpose of the annual updates is to keep the CPI representative over time and to avoid misrepresenting the measured inflation as the index ages.

For the CPI with reference year 2013 = 100, this is the eleventh update in a row. With a chain index, the choice of the reference year, i.e. the year in which the average of the index equals 100, is purely mathematical. The current reference year is 2013, which means that the average of the indices at all levels is 100 for that year.

The representativeness and the quality of the chain index are guaranteed over time, among others by keeping the product basket up-to-date, further refining calculation methods, integrating new price sources and by keeping a representative shop sample.

This is an overview of the changes for 2025. The Index Commission, composed of academics and representatives of the social partners, gave a unanimous positive opinion on this to the Minister of Economy. The Minister follows this opinion and the changes will therefore be implemented by Statbel in the consumer price index of January 2025.

Changes to the CPI in 2025

1. New products in the basket

First, it should be noted that the concept of “representative item” has become obsolete with the use of alternative data sources such as scanner data and webscraping. Indeed, for the relevant product groups, virtually the whole range is now captured, so the “sample” retains its representativeness. Indeed, instead of the traditional items, product segments are now monitored that contain a multiple of the previous items. For example: where previously, for women's footwear, only 3 representative items were monitored, (low shoes, boots and tennis shoes), since 2021, the entire range of footwear is covered via webscraping (ankle boots, boots, laced boots, hiking shoes, sandals, sneakers, slippers, etc.).

In terms of more traditional price recordings, from 2025 the representative item “horse riding lessons” was added to COICOP group 09.4.1.2 “Recreational and sporting services - Participation”.

2. Adaptation of calculation methodology

Three adjustments were made to the calculation methodology, enabling Statbel to meet Eurostat's recommendations.

Plane tickets: in addition to flights from Zaventem, from January 2025 onwards, flights from Charleroi are also monitored for the calculation of the plane ticket index. Price indices for Brussels Airport and Charleroi Airport are aggregated to one index using weights, based on Statbel’s air transport statistics.

Medical fee supplements in hospitals (single room): previously, the “hospitalisation in single room” index was based on the official patient’s contributions and room supplements, while in single rooms, fee supplements are usually also charged. From January 2025, the index for hospitalisations in single room also takes into account fee supplements and all related costs.

Package holidays abroad: the calculation method for package holidays abroad was also adapted. Until now, a summer sample and a winter sample were used. From 2025, a seasonal imputation method (the “all-seasonal estimation”) is used. This is a procedure to obtain an estimated price for an “off-season” destination so that in the first out-of-season month, a typical price from the previous in-season period is used and in the following months, the estimated price is imputed based on the observed prices over all “in-season” destinations. There was also a switch to the use of the geometric mean and a different imputation method when substituting hotels in the sample.

3. Weighting scheme 2025

From 2024 onwards, the 2022 household budget survey, the results of which were published in September 2023, is used.

Since a chain index is used, in which the prices of the twelve months of the current year are compared with December of the previous year, the weighting scheme needs to be adjusted annually to the year of the reference month. This is done using a comparison of the price evolution with the year in which the values are expressed. This procedure is known in professional literature as the “price update” of weights.

So the weights based on the 2022 HBS were updated to December 2024 based on the price evolution of each product group, since December 2024 is the new reference month for the chain index in 2025.

The table below compares the new weights for 2025 with those for 2024. The large fluctuations for the 12 main groups of the index basket are mainly caused by natural gas and electricity (contained in group 4), which result in a decrease in the relative weight of the other groups. The relative share of energy in the index basket goes from 7.87% to 11.41%; an increase of 45%.

Evolution of the basket weights of the index from 2024 to 2025