Welcome to September, historically the worst month for stocks

If you're an investor who knows your market history, you might be tempted to tune out for a bit and start singing Green Day's "Wake Me Up When September Ends." The ninth month is traditionally the worst of the year for stocks.

The market was up slightly Wednesday morning, but the S&P 500 has fallen about 0.5%, on average, during the month of September, according to Ryan Detrick, chief market strategist for LPL Financial. Stocks have tended to go up, on average, during every other month — other than a slight dip in February — over the past half century.