It's Easy! Buy Stocks First of Month Only, Make 28%

Here's an easy way to make money: Only play the market on the first day of the month.

Traders who did so over the past 10 years would find themselves up 28 percent in their portfolios even though the Standard & Poor's 500 has fallen 24 percent in the same period, according to research by Howard Silverblatt, S&P's senior index analyst.

"This thing works," says Silverblatt, who admits he's not 100 percent sure why—though one solution could be flow of funds adjustments at the first of the month.

"The logic is that it's not so much what you make in the good markets but what you lose in the bad."

In the 10-year secular bear market, investors have found themselves groping for ways to make money, at least on the broad market.

But first-day-of-the-month traders—if there are any who would follow such a seemingly arbitrary strategy—have had a much better time.

Since December 1999, 64 percent of first-day trades were up compared to 53 percent of all days. Since January 1926, 57 percent of first-day trades were up compared to 52 percent of all days.

Investors who started with $10,000 would have $12,804, while investors playing the S&P would have seen their bankrolls shrink — to $7,594 for those unlucky enough to stick around for the rest of the month, Silverblatt said.