Market statistics
Overnight against daytime: where the market's return actually happened
Split each day into the move that happens while the market is shut and the move that happens while it is open. In the S&P 500 ETF, essentially the entire thirty-year return is in the overnight half. In the S&P 500 index itself the answer flips completely — and the reason is a detail of how an index open is calculated that almost nobody checks.
1993–2026 for the funds · 1962–2026 for the index
| Instrument | Window | Overnight only | Daytime only | Buy and hold | Overnight volatility | Daytime volatility |
|---|---|---|---|---|---|---|
| SPYSPDR S&P 500 ETF · tracks the S&P 500 | 1993–2026 | +2,421% | +27% | +3,094% | 10.6% | 15.2% |
| QQQInvesco QQQ Trust · tracks the Nasdaq-100 | 1999–2026 | +3,837% | -58% | +1,562% | 14.3% | 23.0% |
| S&P 500 indexThe index itself — no opening trade | 1962–2026 | +118% | +4,840% | +10,678% | 3.6% | 15.6% |
SPY, 1993–2026
- Overnight only
- 25.2x
- +0.040% per session
- Daytime only
- 1.3x
- +0.007% per session
- Buy and hold
- 31.9x
- the two multiplied together
- Overnight up days
- 55.5%
- daytime 52.3%
- Sessions
- 8,452
- since 1 Feb 1993
| Decade | Overnight | Daytime | Whole day | Overnight, per session | Daytime, per session | Sessions |
|---|---|---|---|---|---|---|
| 1990s | +299.0% | -4.3% | +281.9% | +0.080% | +0.001% | 1,748 |
| 2000s | +53.4% | -41.1% | -9.6% | +0.020% | -0.014% | 2,515 |
| 2010s | +128.0% | +54.7% | +252.8% | +0.034% | +0.020% | 2,516 |
| 2020s | +80.6% | +45.2% | +162.2% | +0.039% | +0.027% | 1,673 |
| Decade | Overnight | Daytime | Whole day | Overnight, per session | Daytime, per session | Sessions |
|---|---|---|---|---|---|---|
| 1960s | -1.9% | +31.2% | +28.7% | -0.001% | +0.016% | 1,987 |
| 1970s | +0.7% | +16.5% | +17.2% | 0.000% | +0.010% | 2,526 |
| 1980s | -0.2% | +227.9% | +227.4% | 0.000% | +0.053% | 2,528 |
| 1990s | +0.2% | +314.8% | +315.7% | 0.000% | +0.060% | 2,528 |
| 2000s | -11.7% | -14.1% | -24.1% | -0.005% | +0.003% | 2,515 |
| 2010s | +45.3% | +99.4% | +189.7% | +0.015% | +0.031% | 2,516 |
| 2020s | +72.1% | +38.7% | +138.7% | +0.034% | +0.024% | 1,673 |
Fund figures are total returns from split- and distribution-adjusted prices; the index figures are price levels, which is why its buy-and-hold column is lower for the years the two overlap. Price returns from daily closing levels. Index price returns exclude dividends.
Same question, opposite answers
Take the SPDR S&P 500 ETF since 1993. Compound only the overnight moves — buy at every close, sell at every open — and you get +2,421%. Compound only the daytime moves and you get +27%. Nearly the whole 31.9x return of the fund arrived while the exchange was closed. In QQQ it is starker still: the daytime half has compounded to -58% since 1999 — the hours everyone actually watches have lost money for a quarter of a century.
Now run the identical calculation on the S&P 500 index and it inverts: +118% overnight against +4,840% in the daytime. Both numbers are computed correctly from their series. The difference is that an index has no opening trade — its opening level is assembled from the last available price of each constituent, so every stock that has not opened yet contributes yesterday's close. The gap that really happened is understated, and the move gets booked to the daytime session instead.
That is the whole reason published versions of this comparison contradict each other, and why the instrument matters more than the method. Where the two disagree, the fund is the one describing something a person could have experienced: it has one real opening print, at which real shares changed hands.
Read the volatility columns before drawing a strategy out of it. The overnight half is calm — 10.6% annualised against 15.2% for the daytime — which is a large part of why it looks so good compounded. And capturing it means roughly 250 round trips a year at the two least liquid moments of the session, which is where a pattern of this size goes to die.
Questions people ask about this
- Why do the index and the ETF disagree?
- Because an index has no opening trade. Its opening level is computed from the last available price of every constituent, so any stock that has not opened yet contributes its previous close — which understates the overnight gap and pushes that move into the daytime session instead. A fund has one real opening print. Where the two disagree, the fund is the one describing something an investor could have experienced.
- Could you trade this?
- Only in the sense that you could try. Capturing the overnight half means buying at every close and selling at every open, which is roughly 250 round trips a year: spreads, commissions and the fact that both prints are the least liquid moments of the session eat a pattern this size quickly. The finding is a description of where return has accrued, not a strategy, and the page states the split rather than a backtest with costs it cannot model.
- Why does the index series start in 1962?
- Because that is when a published opening level for the S&P 500 begins. Before it, the data feed fills the open with that day's close, which makes every earlier session look like a zero-return gap followed by the whole day's move. Running this analysis on a full download without noticing adds three decades of fabricated data pointing the wrong way, which is a large part of why the published versions of this comparison disagree with each other.
Sources and method
- Data
- Financial Modeling Prep — Daily adjusted closing levels and quotes, retrieved through Plutux's own data service.
- S&P Dow Jones Indices — Publisher and methodology owner of the S&P 500 index itself.
- How it was calculated
- Each session is split in two: the overnight move is that day's open against the previous close, and the intraday move is the close against that day's open. The two multiply to the daily return exactly, so the split is an identity rather than an estimate. Each half is compounded separately over the whole window and by decade. A year is only included where most of its bars carry an opening price that differs from the close — for the index that begins in 1962, and for the two funds at their inception. Fund figures are from split- and distribution-adjusted prices; index figures are price levels.
- How often it changes
- Regenerated from the full daily history about once a year; the date it runs through is at the top of the page.
- Citing this page
Free to quote — please link rather than copy the table.
Plutux. "Overnight against daytime: where the market's return actually happened." Data through 28 Aug 2026. https://plutux.ai/resources/tools/overnight-vs-intraday-returns
Historical figures for information only — not investment advice, and not a forecast.
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- S&P 500 annual returnsEvery calendar year's price return, the largest drop inside each of those years, and what the distribution of outcomes actually looks like.
Plutux is not an investment adviser. Market data and AI-generated analysis are for information and education only, not investment advice. Disclaimer