What is the lag-time between online stock quotes and the market?

Many of the stock quotes provided in so-called "real time" on financial websites are in fact delayed by as much as 20 minutes, according to Investopedia. Those using these websites should check the time that's posted next to any stock quote to see how accurate the quote is.

Prices can change quickly, so investors may not receive the price they were quoted, as the Securities and Exchange Commission points out. The SEC doesn't post any regulations regarding the time frame in which any trade must be executed, but it does require brokers to avoid exaggeration and to tell investors about potential lag in trades if they advertise themselves as making trades quickly.