An Extended-Hours Trading Primer

Price volatility usually refers to the speed and size of changes in the price of a stock. There may be more volatility in the extended hours sessions than in the standard day session, because of the lack of buyers and sellers.

Price spread generally refers to the difference in prices between what you can buy a security for and what you can sell it for. Lower liquidity and higher volatility sessions may result in wider than normal spreads for a particular security.

If that sounds like a bunch of legal nonsense, it boils down to this: Stocks often make big moves in the after hours that don't hold up. So if you're not careful, you can wake up the next morning to find you've lost a bunch of money.

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