CAC 40 Explained: How the French Stock Index Works
The CAC 40 is the headline number for French shares, quoted on news bulletins whenever markets move. As protests, budget worries and rising bond yields kept France in the news in October 2026, more people started asking what the index actually measures. This explainer covers how the CAC 40 is built, what moves it, how to read it and how investors typically gain exposure to it.
Key takeaways
- The CAC 40 tracks 40 large companies listed on Euronext Paris, weighted by free-float market capitalization.
- It started at a base of 1,000 points at the end of 1987, so the level shows change since then, not a price in euros.
- Many index companies earn much of their revenue outside France, so the CAC 40 is not a pure measure of the French economy.
- Investors usually gain exposure through index funds or ETFs; costs, structure and diversification matter more than the index name.
You hear "the CAC 40 rose" or "the CAC 40 fell" almost every day, but rarely what that means. The index is useful as a quick gauge of how large French-listed companies are valued, and it is the basis for many funds and financial products. Knowing how it works helps you read market news more critically and understand what you own if you hold a French or European fund.
This article is general information, not investment advice. It does not recommend buying or selling any security and does not predict future prices.
What the CAC 40 is
The CAC 40 is the main stock market index of the Paris exchange, operated by Euronext. The name comes from "Cotation Assistée en Continu," the continuous trading system the Paris exchange introduced in the 1980s. The index includes 40 of the largest and most actively traded companies listed on Euronext Paris.
It started at a base value of 1,000 points at the end of 1987. Every movement since then reflects changes in the combined value of the companies in the index, adjusted so that changes to the list of members do not create artificial jumps.
How the index is calculated
You do not need to do the maths yourself, but understanding the method explains why some companies move the index far more than others.
Free-float market capitalization weighting
Market capitalization is a company's share price multiplied by its number of shares. "Free float" counts only the shares available to trade on the market, excluding large blocks held by founders, families, governments or other long-term holders. The bigger a company's free-float market value, the more weight it has in the index.
That means a large company moving 2% can shift the CAC 40 more than several smaller companies moving 5%. A handful of the largest members can drive much of the daily change.
Weight limits and reviews
To avoid any single company dominating, index rules cap the weight of individual members. An independent committee reviews the index regularly and can add or remove companies based on size and trading activity. When a company leaves, another takes its place, and the calculation is adjusted so the index level does not jump because of the change itself.
Price index and total return
The headline CAC 40 is a price index: it reflects share prices but not the dividends companies pay. Euronext also publishes total return versions that assume dividends are reinvested. When comparing performance over long periods, check which version you are looking at, because the difference can be significant.
Common mistake
Comparing the CAC 40 with another index by its point level. An index at 7,800 is not "worth more" than one at 4,000; each started from a different base on a different date. Compare percentage changes over the same period, and check whether dividends are included.
What kinds of companies are in it
The CAC 40 includes many global companies. Major sectors represented include luxury goods, industrials, energy, banks, consumer goods, healthcare and technology. Several of these companies earn much of their revenue outside France, from customers in the rest of Europe, the Americas and Asia.
This has two consequences for investors:
- The index is not a pure measure of the French economy. It can rise while French growth is weak, or fall because of events elsewhere, such as demand in other regions or global interest rates.
- Sector concentration matters. If a few large companies from one sector carry a big weight, news about that sector can move the whole index.
What moves the CAC 40
Many forces affect the index at once. They broadly fall into four groups.
| Driver | How it can affect the index |
|---|---|
| Company results and news | Earnings, guidance, deals and scandals at large members move the index directly |
| Global economy | Demand in Europe, the US and Asia matters for exporters and luxury groups |
| Interest rates and bond yields | ECB decisions and government bond yields affect valuations and bank profits |
| French politics and economy | Budget debates, ratings and domestic growth weigh on domestically focused members |
The 2026 context
As of late October 2026, French politics was firmly among the drivers. The CAC 40 closed at about 7,838 points on 20 October 2026, down 0.4% that day, with reports linking the dip to the unrest that followed the 17 October day of action, the higher OAT yield and budget worries. France's 10-year government bond yield was above 4%, and close to 5% in some reports, while its spread over the German Bund had passed 100 basis points in September for the first time in about 14 years.
Other scheduled events can also matter: the ECB monetary policy meeting on 29 October 2026 and Insee's first estimate of third-quarter growth on 30 October 2026. Search interest in "French stocks" rose sharply in October 2026, according to Google Trends, a sign that many people were looking for exactly this kind of explanation.
Pro tip
When you read that the CAC 40 moved, check which members drove the change. Financial news sites usually list the biggest gainers and losers. You may find that one large company's results, not the wider political situation, explains most of the day's move.
How investors gain exposure to the CAC 40
You cannot buy an index directly, but you can buy products that track it. Here are the most common routes and what to check for each.
- Index funds and ETFs. Exchange-traded funds that track the CAC 40 aim to match its performance, minus fees. Check the ongoing charge, whether the fund holds the shares directly or uses derivatives, and whether dividends are paid out or reinvested.
- Broader European funds. Many investors get French exposure through funds covering the euro area or Europe. These spread risk across more countries.
- Individual shares. Buying single companies means you take on company-specific risk. It requires research and usually more diversification across holdings.
- Derivatives and leveraged products. Futures, options and leveraged products can magnify gains and losses. They are complex and generally unsuitable for most beginners.
Tax treatment depends on where you live and what kind of account you use. In France, for example, some accounts have specific rules about which funds qualify. Check with a tax adviser or official sources such as impots.gouv.fr before choosing an account.
Hypothetical example
Imagine Sophie, a made-up freelance designer in Bordeaux, who already holds a global index fund. She is curious about the CAC 40 after seeing it in the news. Before buying anything, she checks her global fund's country breakdown and finds it already includes French companies. She realizes an extra CAC 40 fund would increase her exposure to one country and a few sectors. She decides to keep her current mix and revisit the question with an adviser. The name and details are invented for illustration.
What a CAC 40 tracker offers
- Exposure to 40 large companies in one product
- Usually low cost and easy to trade
- Access to many globally active businesses
Limits to keep in mind
- Single-country exposure and political risk
- Concentration in a few large companies and sectors
- Not a direct bet on French economic growth
Your CAC 40 understanding checklist
- Remember that the index level shows change from a base of 1,000, not a price
- Compare indexes by percentage change, not point level
- Check whether figures are price only or include dividends
- Look at which large members drove a day's move
- Review your existing funds for French exposure before adding more
- Compare fees, structure and dividend policy of any tracker
- Check account tax rules and speak to a licensed adviser if unsure
Frequently asked questions
Is the CAC 40 a good indicator of the French economy?
Only partly. Many index members are global companies that earn much of their revenue abroad, so the index can diverge from French growth. For the domestic economy, look at Insee data on growth, unemployment and inflation alongside the index.
How often does the list of companies change?
An index committee reviews the composition regularly and may replace companies based on size and trading activity. Changes are announced in advance by Euronext. Funds that track the index adjust their holdings accordingly.
Can foreigners invest in the CAC 40?
Generally yes, through brokers and funds available in their own country. Check currency effects, since the index is in euros, and the tax treatment where you live. Product availability varies by country and platform.
Why did the CAC 40 fall during the October 2026 protests?
Reports linked a dip on 20 October 2026 to the unrest, the higher French bond yield and budget worries. Index moves usually have several causes at once, including company news and global markets. Nobody can reliably say how the index will move next.
Related reading
The bottom line
The CAC 40 is a free-float weighted index of 40 large companies listed in Paris, starting from 1,000 points at the end of 1987. It reflects global business trends as much as the French economy, and a few large members can drive its daily moves. In 2026, French politics and bond yields joined the list of influences. Read the index in context, compare by percentages, understand what any tracker holds and keep your overall portfolio diversified.
