Here's what happens to the stock market during the Olympics

Luke MacGregor/Reuters

Today's entry in fun historical stock-market anecdotes comes from Bespoke Investment Group.

Bespoke broke down the performance for the US's S&P 500 index and the host country's main stock index for every Olympic Games since 1928.

For the US, stocks go up about half the time between the opening and closing ceremonies, according to Bespoke.

"The S&P 500 has averaged a gain of 1.75% from the opening ceremony to the closing ceremony over the 20 Summer Olympics since 1928 (2 of the 22 were cancelled due to world wars)," the note said. "The median return has been smaller at +0.30%, and the index has been positive 55% of the time."

Recent history, however has been more mixed, with stocks gaining twice — in 2004 and 2012 — and falling twice — in 2000 and 2008. The two drops, however, did come during games in the middle of recessions, which is not the case this time around.

For the host countries, markets have generally been more positive.

"Since 1984, the benchmark indices of host countries have averaged a gain of 1.74% (median 2.32%) from the opening ceremony to closing ceremony, with positive returns six out of eight times (75%)," Bespoke said.

The worst performer of the host countries was China in 2008, which saw its massive stock bubble pop and the Shanghai Composite index drop 7.69% during the two weeks of the Olympics.

The best return? The 9.41% jump in the S&P 500 in 1984 when Los Angeles was the host.

It remains to be seen whether Brazil can be one of the luckier hosts. The country still remains in recession, but its stock market has rallied 33% this year, according to Bespoke. The opening ceremony will be held Friday night.

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