Pre-holiday effect

The pre-holiday effect is the historical pattern of stronger equity returns on the session immediately before a market holiday. A mechanical rule is long into that session and flat afterward. It is a one-day calendar effect. It does not identify which holiday will matter this year, and it is small enough that costs decide whether it exists for a given account.

Not investment advice. Nothing here is a recommendation to buy or sell anything. Backtests and historical studies are not guarantees, and a rule that worked in one sample can fail in the next. Trading can lose money. Links are for education, not endorsements. Do your own research.

Rules

Use the exchange holiday calendar for the market you trade. Enter at the prior close, or at a stated time on the prior day, and exit at the close before the holiday or at the next reopening, whichever the test specifies. Trade it only in a liquid index vehicle. Skip years in which you only keep the holidays that worked.

Where AI fits

AI can build the holiday calendar from the exchange, not from memory, and can include early closes. It can net out a realistic spread on a one-day hold. If the result disappears after costs, the model should say so. Cherry-picking Christmas and ignoring the rest is not the strategy.

Markets

Liquid equity-index futures or ETFs. Single stocks are a noisier version of a one-day effect.

Timeframes

One session before each scheduled holiday.

Risks

A one-day edge is the first thing commissions and spreads remove. Holidays coincide with thin books and with macro releases. The pattern can decay once it is published. A backtest that uses today's holiday list incorrectly for old years will mislabel sessions.

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