Day TradingUpdated daily after close · as of 2026-06-24
Weekday Analysis: SPY Returns by Day of Week & Overnight vs Intraday
How the S&P 500 (via SPY) trades on each weekday, split into the intraday session (open → close) and the overnight gap (prior close → open). The headline finding is the overnight drift: nearly all the long-run gain has accrued overnight while the regular session is roughly flat.
Today's reading
As of market close on June 24, 2026, across 8,405 SPY trading days since 1993, compounding only the overnight (close→open) returns grew $100 to $1464, versus just $113 for the intraday (open→close) session — the overnight-drift anomaly. By weekday, Monday has the highest intraday win rate (52.5%) and Tuesday the lowest (50.9%).
Source
SPY daily open/close from our price database (1993–present)
Methodology
Intraday = close/open−1 by weekday; overnight = open/prevClose−1 by transition; avg, bull/bear avg, win rate, sample count per bucket
Updates
Daily after US market close (~1pm PT)Last: 2026-06-24
Window:loading full history…
Intraday win rate
51.7%
8,405 trading days
Best day (intraday)
Monday
52.5% win rate
Worst day (intraday)
Tuesday
50.9% win rate
Best overnight
Monday→Tuesday
+0.07% avg
01
Cumulative returns — overnight vs intraday
Two equity curves, both starting at 100: one compounds only the intraday (open→close) returns, the other only the overnight (close→open) returns. If the blue line runs away from the green, the market's gains are happening while it's closed.
Loading equity curves…
Intraday (open → close) Overnight (close → open)Start = 100
Intraday returns (open → close)
By weekday
| Day | Avg | Bull avg | Bear avg | Win rate | Samples |
|---|---|---|---|---|---|
| Monday | +0.02% | +0.60% | -0.66% | 52.5% | 1579 |
| Tuesday | +0.01% | +0.65% | -0.69% | 50.9% | 1727 |
| Wednesday | +0.02% | +0.64% | -0.69% | 52.4% | 1725 |
| Thursday | -0.00% | +0.64% | -0.71% | 51.3% | 1691 |
| Friday | -0.01% | +0.60% | -0.69% | 51.3% | 1683 |
Overnight returns (close → open)
By session transition
| Day | Avg | Bull avg | Bear avg | Win rate | Samples |
|---|---|---|---|---|---|
| Friday→Monday | +0.05% | +0.44% | -0.48% | 56.0% | 1520 |
| Monday→Tuesday | +0.07% | +0.43% | -0.38% | 54.9% | 1565 |
| Tuesday→Wednesday | +0.04% | +0.38% | -0.41% | 56.7% | 1710 |
| Wednesday→Thursday | +0.02% | +0.40% | -0.44% | 53.7% | 1674 |
| Thursday→Friday | +0.01% | +0.43% | -0.50% | 54.1% | 1633 |
How Weekday Analysis Works
- 1Split each SPY day into two return streamsFor every trading day we compute the intraday return (close ÷ open − 1) — what the regular session delivered — and the overnight return (open ÷ prior close − 1) — the gap that opened while the market was shut. Together they make up the full close-to-close move.
- 2Bucket by weekday and by session transitionIntraday returns are grouped by weekday (Monday–Friday). Overnight gaps are grouped by transition — Friday→Monday (the weekend gap), Monday→Tuesday, and so on — because the weekend gap behaves differently from a weeknight.
- 3Compute the distribution per bucketFor each weekday and transition we report the average return, the average of up days only (bull avg) and down days only (bear avg), the win rate, and the sample count — so you can see not just the mean but the shape of the distribution and how many observations back it.
- 4Compound two equity curves: overnight vs intradayStarting from 100, one curve compounds only the intraday returns and the other only the overnight returns. The gap between them is the headline: over the long run the overnight curve runs far above the intraday one — the "overnight drift" anomaly, where the market does its rising while it is closed.
Who Uses Weekday Analysis
Day Traders
Know which sessions historically pay. If the regular session is a coin flip while the gains happen overnight, that reframes the case for holding through the close versus flattening into it.
Swing Traders
Decide when to add or trim around the week — the weekend (Friday→Monday) gap and the Tuesday→Wednesday gap have historically been the strongest overnight windows.
Systematic Traders
A clean base rate for calendar and session filters. Build the overnight-vs-intraday split into entry/exit rules, or test whether a strategy is unknowingly capturing the overnight drift.
Skeptics
Stress-test the anomaly yourself: shorten the window to recent years and watch whether the day-of-week edges hold up or wash out. The sample counts keep you honest.
Pro Tips
01
The overnight drift is the real story
Day-of-week effects are interesting but noisy and regime-dependent. The persistent, well-documented finding is that almost all of SPY's long-run return has come overnight (close→open), with the regular session roughly flat. Watch the blue vs green equity curves over the full window.
02
Read win rate and average together
A day can have a positive average but a sub-50% win rate (a few big up days carry it) or vice versa. The bull avg and bear avg columns show which: a small bull avg with a large bear avg means the down days hurt more than the up days help.
03
Shorten the window to check regime
Use the window selector to see whether an edge is structural (holds across 1Y / 5Y / Max) or a recent fluke. Anything that flips sign across windows is noise, not a signal.
04
Mind the sample size
Over a single year each weekday has only ~50 observations, so win rates swing widely. The Max window (8,000+ days since 1993) is where the statistics are trustworthy.
Common Issues & Solutions
Can I actually trade the overnight return?▾
Not for free. The overnight-vs-intraday split is a clean academic decomposition assuming you transact exactly at the close and the open; in practice spreads, slippage and the inability to trade the literal print eat into it. Treat it as evidence of where return accrues, not a turnkey strategy.
Why do the day-of-week numbers change with the window?▾
Day-of-week effects are not stable — they drift and even reverse across decades. The tool recomputes every statistic for the window you select, so a shorter window shows the recent regime and the Max window shows the full 1993-present record.
Why SPY and not QQQ or my stock?▾
SPY is the canonical US-equity benchmark with the longest clean history (back to 1993), giving the largest samples. The overnight drift is broad-market; it appears in QQQ and most large-cap names too, often even more strongly in QQQ.
What counts as "overnight"?▾
The change from one day's closing price to the next session's opening price — the gap that forms outside regular trading hours, including after-hours and pre-market repricing plus any weekend or holiday in between.
Frequently Asked Questions
What is the overnight drift?▾
The well-documented finding that, for broad US equity indices like the S&P 500, almost all of the long-run gain has accrued overnight — between the prior session's close and the next session's open — while the regular trading session (open to close) has been roughly flat. This tool visualizes it by compounding the two return streams into separate equity curves.
How are intraday and overnight returns defined?▾
Intraday return = today's close ÷ today's open − 1 (what the regular session delivered). Overnight return = today's open ÷ yesterday's close − 1 (the gap that formed while the market was closed). Chained together they reproduce the full close-to-close return.
Which day of the week is best for the S&P 500?▾
It depends on the window — day-of-week effects shift over time. The tool ranks each weekday by intraday win rate and average return for the period you select, and ranks the overnight transitions (Friday→Monday, etc.) separately. Use the Max window for the most statistically reliable read.
Why does the weekend gap (Friday→Monday) get its own bucket?▾
Because it spans two non-trading days plus a weekend of news flow, the Friday→Monday gap behaves differently from a single weeknight. Grouping it separately avoids mixing a 3-calendar-day gap in with overnight gaps.
Is this a trading strategy?▾
No — it is a statistical study. The overnight/intraday decomposition assumes frictionless execution at the open and close; real costs erode the edge. It is best used as context (where does return come from, which sessions are weak) rather than as a standalone system.
How often is it updated?▾
Daily after the US market close, from the same SPY price history that powers the rest of the site. All statistics reflect data through the most recent close.
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Last updated: 2026-06-24