"If you take all of the Octobers since 1970 and average them out, it is the second-worst performing month in the Dow Jones Industrial Average," Winans said.
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"What is worse?" we asked. "September is typically worse."
If you're wondering about the mechanics of the drop, financial experts describe this as a rebalancing act. Stocks have performed well for a long time while interest rates have been low.
Now, there's a change in equilibrium.
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"As interest rates go up it re-prices bonds, puts temporary pressure on stocks," Winans said.
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Edwards says it's not time to worry about the sky falling like Chicken Little.
"The S&P is at an all-time high. This is not stuff you panic about," he said.
That includes people with fixed incomes counting on a 401k. The good news for them is that while September and October stock prices historically trend low, in November, December, January, they move up.
In short - you might not want to panic, even if the market opens lower Thursday.