Don't Sell in May?

One old maxim for stock market investors has been "Sell in May, then go away." The idea is that the market tends to spend the summer in the doldrums, and then picks back up in the fall.

But that hasn't been true this year. Though the stretch between May and October is typically thought to be weak for the stock market, equities have started off that period on a strong note. The S&P 500 has climbed 4.7 percent since the end of April, the best performance for that stretch since 2009.

The maxim does have some validity. Over the last two decades, the S&P 500 has climbed 0.3 percent on average between May and October, versus 6.5 percent between November and April. But over the last five years, the S&P 500 has actually performed better between between May and October than between November and April.