The Indexeuro PX1 is the mnemonic code used on trading platforms to refer to the CAC 40, the flagship index of the Paris Stock Exchange. This technical code, often encountered in financial data streams, designates exactly the same basket of values as the CAC 40. Understanding what this designation encompasses allows for a proper reading of a trading screen and interpreting movements in the French stock market.
Free Float Capitalization and Weighting Cap per Share: The Calculation Behind the Indexeuro PX1
Most presentations of the Indexeuro PX1 simply state that it includes the forty largest French capitalizations. The calculation mechanism deserves more precision, as it directly conditions the actual weight of each company in the index.
The index is weighted by free float, meaning the portion of capital that is actually available for buying and selling on the market. Shares held by the state, founders, or locked in shareholder agreements do not count in this calculation. A company with a very high total capitalization but a limited float will therefore weigh less in the index than one might assume.
A little-documented mechanism in educational content is the weighting cap set at 15% per share. This threshold, revised annually, prevents any single stock from excessively dominating the overall performance of the index. When the free float capitalization of a group exceeds this cap, its weight is mechanically reduced in the next revision. You can learn more about the indexeuro PX1 and how this capping influences the reading of the index.
Sector Concentration of the PX1: Industry and Finance at the Forefront
An index of forty stocks does not guarantee balanced diversification across sectors. The actual exposure of the Indexeuro PX1 leans significantly towards certain segments of the economy, and this distribution has practical consequences for anyone using the index as a reference.
Allocation data collected from several ETFs replicating the CAC 40 (Amundi CAC 40, Lyxor CAC 40, EasyETF CAC 40) show a lasting overweighting of the industry and financial services. These two sectors concentrate a significant share of the total weight, ahead of luxury, health, or energy.
This sectoral structure means that a rise or fall in French industrial and banking stocks moves the index much more than a similar movement in technology or utility stocks would. For an investor following the Indexeuro PX1 as a barometer of the French economy, this sectoral reading is more relevant than the simple figure displayed at the end of the session.
A Concentration Phenomenon on a Few Mega-Stocks
Beyond sectors, concentration is also observed at the level of individual companies. A few large French groups alone account for a considerable share of the index. This phenomenon has intensified in recent years, driven by the growth of the capitalization of certain luxury and industrial stocks.
The 15% cap partially mitigates this effect, but it does not eliminate it. Five to six companies can represent more than a third of the total weight of the index. In practice, following the PX1 partly means tracking the trajectory of these few groups. The thirty-five other stocks, taken individually, have a marginal impact on overall performance.
Variants of the CAC 40: Reinvested Dividends or Not
The PX1 code designates the “naked” version of the index, which only takes into account the evolution of prices. This version is the most cited in the media. It has a structural bias: it ignores the dividends paid by the companies in the basket.
Two other versions exist that correct this bias:
- The CAC 40 GR (Gross Return) reintegrates gross dividends into the performance calculation, as if each dividend were immediately reinvested in the index.
- The CAC 40 NR (Net Return) performs the same calculation but after deducting withholding tax on dividends, which better reflects the actual yield perceived by a non-resident investor or one subject to standard taxation.
The difference between the naked PX1 version and the GR version is far from negligible over the long term. The dividends paid by the forty companies in the CAC 40 represent a significant annual yield. Over ten or twenty years, the GR version shows a performance significantly superior to the naked version, sometimes by a factor of two. Therefore, comparing a portfolio of French stocks to the PX1 alone systematically underestimates the actual performance of the market.
Using the Indexeuro PX1 to Manage a Stock Portfolio
The index serves as a benchmark for evaluating the performance of a fund or portfolio invested in French stocks. A manager who performs worse than the PX1 over a given period has not justified their management fees compared to a simple ETF replicating the index.
For a retail investor, three concrete uses emerge:
- Comparing the performance of their PEA or securities account to the evolution of the PX1 over the same period, choosing the right version (GR if dividends are reinvested).
- Identifying a sectoral bias in their portfolio compared to the composition of the index: an overexposure to French technology stocks, for example, decouples performance from the benchmark.
- Spotting market phases (uptrend, correction, consolidation) by observing the history of the PX1 rather than following each stock individually.
The Indexeuro PX1 is not a prediction tool. It reflects the state of the market at a given moment, weighted by the size of the companies that compose it. Its reading gains relevance when integrating the sectoral structure, the weighting cap per share, and the choice between naked version or reinvested dividends. These three parameters transform a simple figure displayed on a trading screen into a true analytical tool.