If it feels like the market opens lower every morning lately, it's because it has been. Below is a chart highlighting the 20-day moving average opening gap for the S&P 500 SPY ETF. We also highlight the 20-day moving average open to close change for SPY. As shown, over the last 20 days, SPY has opened lower by an average of 0.13% each day. From the open to the close, however, the ETF has actually averaged a small gain of 0.03%.
Interestingly, the market has been getting weaker and weaker in after-hours trading since the year began. At the end of 2011, SPY was routinely gapping up at the open by a wide margin as evidenced by the 20-day average gap of more than 0.50%. Since peaking at the end of 2011, the 20-day average gap has drifted lower and lower. Clearly overseas markets, which open for trading well before we open here, are driving share prices here in the US these days.