The Opening Gap on European Indices: a 7-Point Checklist

At 09:00 Paris time the CAC 40 and the DAX sometimes open well away from the previous evening's close. That jump is the opening gap. It is not a signal in itself, but it changes risk for anyone holding a position overnight or trading the first minutes. Here is a seven-point checklist to go through before the open.

Why European indices gap

Between 17:30 and 09:00 the cash market is closed, yet the world keeps moving: Wall Street trades until 22:00 Paris time, Asia trades overnight, companies publish results before the open, and macro data can come out at 08:00. Products with extended hours absorb that news, and the cash index catches up at the opening auction.

The checklist

1. Measure the gap in points and in percent. Compare the pre-open indication with yesterday's close. A 40-point gap on the DAX and on the CAC 40 is not the same size in percent.

2. Find the reason. Overnight US move, company results, a political event, a data release? A gap with an identifiable cause is easier to put in context than a mystery.

3. Check the heavyweights. On the CAC 40 a few large members can create most of the gap (see what the CAC 40 is). If one of them reported, the index gap may be mostly that stock.

4. Check the dividend calendar. On a price index, a large ex-dividend day creates a mechanical drop that looks like a gap but carries no news (ex-dividend dates and index prices).

5. Re-check your open positions. If the open is beyond your stop, the stop becomes a market order and the fill can be worse than planned. Know your maximum loss in that case.

6. Decide your first-minutes rule in advance. Some traders wait 15 or 30 minutes after 09:00; others trade the open with a smaller size. Write the rule; do not decide in the moment.

7. Size for the wider range. The first minutes often move more. Use a wider stop and a smaller size, calculated with the lot size calculator.

A worked example of gap risk

Item	Value
Position held overnight	€2 per point
Planned stop	50 points away = €100
Index opens 90 points beyond entry	Loss ≈ 90 × €2 = €180

Illustrative calculation, not an expectation of results. The stop did its job, but the gap almost doubled the planned loss. This is why some traders cut size before results or major events, or close before 17:30.

Gaps do not "always fill"

A common belief says every gap fills the same day. Sometimes it does, sometimes the market keeps going. Treat any gap rule as a hypothesis to test on at least 100 past examples before you trust it, and record the results in your journal.

Where gaps fit in your day

Gaps belong to the opening window of your schedule. Our guide to European index hours in Paris time shows where 09:00, 14:30 and 15:30 fall, and the market sessions tool shows which markets are open right now.

Recap

Measure, explain, check heavyweights and dividends, review open risk, apply a written first-minutes rule, size for a wider range. Nothing here predicts the direction of the open. Trading involves risk, and most retail traders lose money.