Ex-Dividend Dates and Index Prices: Why the CAC 40 Drops in Spring

Every spring, French companies pay most of their annual dividends, and on some mornings the CAC 40 opens lower without any bad news. Nothing has gone wrong: the index is simply losing the cash that has left the companies. Understanding this mechanism avoids reading a dividend as a market move.

What happens on an ex-dividend date

On the ex-dividend date, a share starts trading without the right to the upcoming dividend. Its price usually opens lower by roughly the dividend amount, because the buyer no longer receives that cash.

For a price index such as the CAC 40 or the Euro Stoxx 50, the index is calculated from those share prices, so it drops too, in proportion to each company's weight. A performance index such as the DAX assumes the dividend is reinvested and does not drop (see the DAX explained).

A worked example

Imagine, for illustration, an index at 7,500 points in which one member weighing 6% pays a dividend equal to 3% of its share price.

Step	Calculation	Result
Drop of the share	3%	−3%
Effect on the index	6% × 3%	−0.18%
In points	7,500 × 0.18%	about −13.5 points

Illustrative calculation, not an expectation of results. On a day when several heavyweights go ex-dividend together, the mechanical effect adds up and can reach dozens of points.

Why the season matters in France

Many large French companies pay once a year, after their annual general meeting, so ex-dividend dates cluster between April and June. During that period the CAC 40 can look weaker than the DAX on a chart, even when the companies themselves have performed similarly. Comparing the two indices over that season without adjusting is comparing apples and oranges.

How instruments that follow the index handle it

Instruments based on a price index do not all treat dividends the same way:

• Futures already price in expected dividends up to their expiry, so their price sits below the cash index by roughly those dividends (plus or minus financing).
• Other products may apply a cash adjustment to open positions on the ex-date: a debit for one direction, a credit for the other.
• ETFs either distribute dividends to holders or reinvest them, depending on the share class.

The exact treatment is in your provider's documentation; read it before holding a position through the dividend season.

What to do in practice

1. Before May, list the ex-dividend dates of the index heavyweights (published by the companies and by Euronext).
2. On those days, do not read the opening drop as information (opening gap checklist).
3. Recalculate the risk on open positions if an adjustment is applied, using the risk-reward calculator.
4. Keep sizes consistent with the lot size calculator: the stop should not be inside the expected dividend drop.

In short

A price index drops by its weighted dividends on ex-dates; a performance index does not. The French dividend season concentrates those drops in spring. Know the calendar, read your instrument's dividend policy and never mistake a mechanical move for a signal. Trading involves risk, and most retail traders lose money.