Is There a Best Day of the Week to Buy Stocks? The Monday Effect, Counted on Every S&P 500 Day Since 1950

Is there a best day of the week to buy stocks? For most of the last 76 years the answer was "not Monday". From 1950 through 2026 the S&P 500 has lost 0.045% on the average Monday and risen on only 49.6% of them, the only weekday with a negative average and the only one that fell more often than it rose. Wednesday and Friday were the best days. Eleven of the twenty worst days in the whole record were Mondays, including the worst of all.

That is the Monday effect, one of the oldest anomalies in finance. We counted it from every daily close since January 1950, 19,318 trading days, and then did the thing most articles skip: we split the record in two. Since 2000 the effect has disappeared. Mondays have been positive on average and up 54% of the time, no worse than any other day, and in 2026 so far Monday has been the best day of the week. This guide gives the full weekday table, where the Monday effect came from, when it faded, what remains true about weekdays, and what any of it should change about how you trade. It is education, not advice.

Every weekday since 1950

Close-to-close change on each weekday, January 1950 through October 15, 2026, price only. Monday's figure is the move from Friday's close to Monday's close, so it carries the whole weekend.

• Monday: -0.045% average, up 49.6% of the time (3,696 days). Worst -20.5% (1987), best +11.6% (2008).
• Tuesday: +0.044% average, up 50.9% of the time (3,940 days). Worst -5.7% (2008), best +10.8% (2008).
• Wednesday: +0.077% average, up 55.6% of the time (3,939 days). Worst -9.0% (2008), best +9.5% (2025).
• Thursday: +0.035% average, up 53.3% of the time (3,884 days). Worst -9.5% (2020), best +6.9% (2008).
• Friday: +0.067% average, up 56.1% of the time (3,859 days). Worst -6.8% (1988), best +9.3% (2020).

Compounded, the gap is startling. $100 invested only on Mondays since 1950 (buy at Friday's close, sell at Monday's close, every week) would be worth about $15 today. The same $100 invested only on Wednesdays would be about $1,758, and only on Fridays about $1,123. The Monday number is dragged down by a handful of crashes, but even the median Monday is the weakest of the five.

The crash days are the other half of the story. Of the twenty worst single days since 1950, 11 were Mondays, against 3 Thursdays, 3 Wednesdays, 3 Fridays and no Tuesdays. The worst day in the record, October 19, 1987, was a Monday (-20.5%). Bad news accumulates over a weekend with no market open to absorb it, and Monday pays the bill all at once.

Then and now: the Monday effect faded

From 1950 to 1999 the average Monday lost 0.079% and rose only 47.4% of the time, while Wednesday (+0.100%) and Friday (+0.098%) were strong. Since 2000 the picture is flat: Monday +0.022% (up 54%), Tuesday +0.059%, Wednesday +0.035%, Thursday +0.034%, Friday +0.008%. The spread between the best and worst weekday fell from about 0.18 percentage points a day to about 0.05, which is inside the noise. Since 2010 Monday has actually been the second-best day (+0.047%, up 56%).

The decade-by-decade share of up Mondays tells the same story: 1950s 44%, 1960s 40%, 1970s 45%, 1980s 50%, 1990s 57%, 2000s 51%, 2010s 52%, 2020s 60%. A day that rose two times in five in the 1960s rises three times in five in the 2020s.

In 2026 through October 15, Monday has been the best weekday, +0.239% on average and up 60% of the time, while Tuesday (+0.006%, up 44%) and Wednesday (+0.030%, up 42%) have been the weak ones. One year is too few days to mean anything, which is exactly the point about weekday patterns in general.

Why the Monday effect existed, and why it went away

• Weekend news. Companies and governments historically released bad news after Friday's close, so the first chance to sell was Monday. Regulators and the companies themselves have moved toward fairer timing, and today the market reacts to weekend news in futures and in the first minutes of trading rather than across a whole day.
• Settlement and short selling. Older settlement rules and limits on short selling made Monday a day of forced selling in the mid-century market. Those mechanics are gone.
• It was published. Once an anomaly is documented, traders trade against it until it is gone. The Monday effect was written up in academic journals in the 1970s and 1980s; the decade table above shows it weakening from the 1990s onward.

What is still true about weekdays

Direction by weekday is now a coin flip with a slight tilt, roughly the same tilt the market has every day. Size is not. Mondays still hold more of the record's largest moves in both directions, because weekend news arrives in one lump, and the biggest up day in the Monday column (+11.6% on October 13, 2008) sits a year apart from the biggest down day. If you hold positions over weekends, the honest expectation is not a lower return but a wider range on Monday morning. Friday remains a day many traders trim risk for exactly that reason, which is one of the few weekday habits with a mechanical basis.

What this should change about your trading

• Nothing about when you buy. A weekday edge of a few hundredths of a percent, which no longer exists anyway, is below the spread and commissions you would pay to exploit it. Our time-of-day study reached the same conclusion inside the trading day.
• Something about how you size over weekends. A position should be able to take a Monday gap. If the weekend worries you, the cure is a smaller position or a defined stop, not a calendar rule. Position sizing covers the math; our drawdown study shows how deep the Monday-led episodes went.
• Automate the schedule and forget it. If you invest a fixed amount on a fixed day, the day does not matter. Dollar-cost averaging works because of consistency, not because of the weekday; the bigger question is lump sum versus averaging in, which we tested on the same data.
• Look at the calendar effects that still measure larger. The gap between the strongest and weakest months of the year is far larger than any weekday gap; our seasonality study ranks all twelve, and even that is a tilt, not a signal.

JorgAI does not time weekdays. It enforces the rules that do matter on a Monday morning: the stop, the position cap and the daily loss limit, inside your own brokerage account, whatever day the news lands. Set your rules once and they hold on the weekend gap.

Quick answers

What is the best day of the week to buy stocks? Historically Wednesday and Friday had the highest average returns and Monday the lowest (-0.045% on average since 1950). Since 2000 the differences have been too small to trade; in 2026 so far Monday has been the best day.

What is the Monday effect? The tendency of stocks to fall on Mondays. From 1950 to 1999 the S&P 500 lost 0.079% on the average Monday and rose on only 47% of them; it was the only negative weekday. Since 2000 the average Monday has been positive (+0.022%).

Does the Monday effect still exist? Not in the index. Mondays have risen 54% of the time since 2000 and 56% since 2010, in line with the other weekdays. What persists is size: Mondays still carry more of the largest moves because weekend news arrives at once.

Which weekday has the biggest crashes? Monday. 11 of the 20 worst days since 1950 were Mondays, including October 19, 1987 (-20.5%).

Is Friday a good day to sell stocks? Friday has had the second-highest average return since 1950 and rises about 56% of the time, so there is no return-based reason to sell on Fridays. Some traders reduce size on Fridays to avoid the weekend gap, which is a risk decision, not a return one.

Data: S&P 500 daily closes from Yahoo Finance (ticker ^GSPC), January 3, 1950 through October 15, 2026, grouped by the weekday of each close; each day's return is the change from the previous trading day's close, so a Monday carries the weekend and a day after a holiday carries the holiday. Price only, no dividends. Past patterns do not predict future returns. This article is education, not investment advice.