Overnight Edge in SPY: A Simple Close-to-Close Strategy

Key Takeaways

• SPY close‑to‑close yields average 0.25% daily return.
• Strategy achieved 5.8% CAGR over 30‑year backtest.
• Transaction costs assumed at 0.06% per trade.
• Max drawdown limited to 16% during period.
• Only 10% of time capital is actively invested.

Pulse Analysis

Academic research and market data consistently show that a sizable share of equity index performance originates from price moves that occur outside regular trading hours. The so‑called “overnight effect” reflects the market’s reaction to after‑hours news, earnings releases, and macro‑economic announcements that are digested while the exchange is closed. Because the SPDR S&P 500 ETF (SPY) tracks the broad U.S. market, it serves as a convenient vehicle for testing whether this edge can be captured in a systematic, low‑maintenance strategy.

The backtest presented in the article spans 1995‑2025, a 30‑year window that includes multiple bull and bear cycles. Positions were entered at the closing price and liquidated at the next day’s close, with a realistic commission of 0.06 % per trade applied to each leg. The results show an average daily gain of 0.25 %, translating to a compound annual growth rate of roughly 5.8 % while the portfolio was exposed only 10 % of the time. The maximum drawdown of 16 % suggests a modest risk profile relative to the return stream.

For investors seeking a hands‑off tilt toward the overnight premium, the close‑to‑close SPY model offers a simple entry point, but it is not without caveats. The strategy’s reliance on daily price gaps makes it vulnerable to sudden macro shocks that can widen overnight moves beyond historical norms. Moreover, the modest time‑in‑market exposure means the approach may underperform during strong intraday rallies. Combining the overnight edge with complementary intraday tactics or using it as a diversification layer can enhance overall portfolio resilience while preserving the low‑maintenance appeal.