Was bedeutet Overnight und Intraday bei Aktien?

Die Tagesrendite einer Aktie lässt sich in zwei Fenster zerlegen. Die Overnight-Rendite entsteht zwischen dem Schlusskurs eines Tages und der Eröffnung des nächsten Handelstages, also außerhalb der regulären Börsenzeit. Die Intraday-Rendite entsteht zwischen Eröffnung und Schluss desselben Tages, während die Börse geöffnet ist. Zusammen ergeben beide die Gesamtrendite. Historisch trägt bei vielen US-Werten das Overnight-Fenster den Großteil der langfristigen Rendite.

Wie wird die Overnight-Rendite berechnet?

SeasonAlpha berechnet die Overnight-Rendite als Residual: Overnight gleich Gesamtrendite minus Intraday-Rendite. Die Intraday-Rendite ergibt sich sauber aus Eröffnung und Schluss desselben Tages, die Gesamtrendite aus zwei aufeinanderfolgenden Schlusskursen. Dieser Residual-Ansatz vermeidet, Kurse zweier verschiedener Tage direkt zu verrechnen, weil sich dazwischen Anpassungsfaktoren etwa durch Dividenden ändern können und sonst ein Verzerrungseffekt entstünde. Alle Renditen werden normalisiert ausgewertet, nicht als absolute Kursdifferenzen.

Warum trägt das Overnight-Fenster oft den Großteil der Rendite?

Bei vielen US-Aktien und Index-ETFs konzentriert sich der langfristige Kursgewinn auf die Zeit außerhalb der Handelssession. Eröffnungskurse liegen historisch häufig über dem Vortagsschluss, während die Bewegung innerhalb des Tages im Mittel flacher verläuft. Dieses Muster ist gut dokumentiert, aber kein Naturgesetz: Es variiert je nach Titel, Zeitraum und Marktphase und lässt sich wegen Geld-Brief-Spannen, Gebühren und Slippage nicht ohne Weiteres als Strategie umsetzen.

Overnight vs. Intraday — SPY

Where does performance come from — overnight (Close→Open) or intraday (Open→Close)?

Methodology

Data Basis

Data source: Supabase (Yahoo Finance OHLC), updated daily
Requires: Open + Close prices (OHLC)
Period: Selectable 5–30 years or Max

Calculation

Overnight: (Open[t] / Close[t−1] − 1) × 100 — Return overnight (gap)
Intraday: (Close[t] / Open[t] − 1) × 100 — Return during the trading session
Total: Overnight + Intraday (residual approach, no cross-day OHLC)
Cumulative: Product of daily (1 + r/100), grouped by day of year

Interpretation

Many indices (SPY, QQQ) generate the majority of their return overnight
Intraday traders miss out on this structural advantage
Seasonal patterns can differ between Overnight and Intraday

Note

Open prices from Yahoo Finance are not always perfectly split-adjusted
The trends are nonetheless statistically meaningful over longer time periods

Understanding Overnight vs. Intraday — Return Split, Reading & Methodology

The Overnight vs. Intraday tool from SeasonAlpha splits a stock's or ETF's total return into two distinct windows. The overnight return covers the time between one day's close and the next day's open — the hours when the exchange is closed. The intraday return spans the regular session, from open to close of the same day. Together they form the total return, revealing when a stock's performance actually accrues: overnight or during trading. Historically, for many US names such as SPY, QQQ or large single stocks, the overnight window carries the majority of long-term returns — a pattern that surprises many investors.

The easiest way to read the split is via the KPI bar and the charts. The overnight share shows what percentage of the aggregated move falls on the night window; a share well above 50 percent means the asset earns its return mainly outside trading hours. In the monthly and weekday bar charts, overnight, intraday and total sit side by side, so you can see whether a seasonal pattern lives in the night or the session. The cumulative yearly path sums both components across the year and shows how far the overnight and intraday curves diverge. The heatmap and the significance test round out the picture: the latter uses a t-test to check whether the overnight effect is systematically different from zero or mere noise.

Methodologically, SeasonAlpha computes the split via a deliberate residual approach: the intraday return is derived cleanly from open and close of the same day, the total return from two consecutive closes — and the overnight return is formed as the difference (Overnight = Total − Intraday). This avoids pricing open against the prior close directly: such a cross-day OHLC comparison would mix prices with different adjustment factors and create a systematic bias on dividend or split days. All analyses rest on normalized returns, not absolute price differences, so assets of different price levels and periods stay comparable. Data comes from daily-updated OHLC prices; an optional technical filter restricts the analysis to specific market phases.

As insightful as the split is, it has limits. The overnight effect is a statistical pattern of the past, not a tradable guarantee. Exploiting it would require buying at every close and selling at every open; in practice bid-ask spreads, fees and slippage consume much of the theoretical edge. Open prices also depend on data quality and are not always perfectly split-adjusted. The effect's strength and sign vary considerably by asset, period and market regime. This tool is therefore a descriptive analytical instrument for context, not investment advice or a trading recommendation. Past patterns do not guarantee future results — use the analysis as context for your own research.

Frequently Asked Questions

What do overnight and intraday mean for stocks? Daily return splits into two windows. The overnight return forms between one day's close and the next day's open, outside exchange hours. The intraday return forms between open and close of the same day, while the exchange is open. Together they make the total return. Historically, for many US names the overnight window carries the bulk of long-term returns.

How is the overnight return calculated? SeasonAlpha uses a residual approach: Overnight = Total − Intraday. The intraday return follows cleanly from open and close of the same day, the total from two consecutive closes. No prices from two different days are netted directly — this avoids a bias from changing adjustment factors, e.g. on dividend days. All returns are evaluated normalized, not as absolute price differences.

Why does the overnight window often carry most of the return? For many US stocks and index ETFs, long-term gains concentrate outside the session; opens historically tend to sit above the prior close while the intraday move is flatter on average. The pattern is well documented but no law of nature: it varies by asset, period and market phase and is not readily tradable due to spreads, fees and slippage.