Education
What Is the 'Monday Effect'? Why the First Trading Day Behaves Differently
Stock markets have a long-documented tendency to behave differently on Mondays than other weekdays. Here's what the effect actually is — and why it's gotten weaker over time.
The 'Monday effect' (sometimes called the 'weekend effect') refers to a historical tendency for stock market returns on Monday to be, on average, lower than returns on other weekdays — a pattern first documented in academic finance research decades ago and observed across multiple different markets and time periods.
Several explanations have been proposed for why this happens, none universally agreed upon: companies have historically tended to release bad news after Friday's close (when it draws less immediate attention) rather than before it, giving Monday's open more negative news to digest; individual investor sentiment has been observed to run more pessimistic at the start of the week than by Friday; and two full non-trading days give more time for negative developments to accumulate and get priced in all at once when trading resumes.
The effect is a good example of a well-documented historical pattern that doesn't necessarily hold up as a reliable trading edge today — since it became widely known and published, its statistical strength has weakened considerably in more recent decades, consistent with a broader pattern in market research where a publicly known anomaly tends to shrink or disappear once enough traders start positioning to exploit it.
Crypto markets, notably, don't have this specific effect at all in the same form, since they never close — a useful reminder, on Trade2Spike's Markets pages, that patterns tied to a market's actual trading-hours structure don't automatically transfer to a market with a different structure.