Trading hours on the principal American stock markets, the New York Stock Exchange -- now called NYSE Euronext -- and the Nasdaq electronic system, are Monday through Friday from 9 a.m. until 4 p.m. Eastern time. Both markets also have "premarket" operations and extended hours until 8 p.m. The only regular exceptions to the closing hours are the day before July Fourth, Thanksgiving and Christmas when regular trading ends at 1 p.m.
Some private electronic communications networks offer after-hours trades by matching buy and sell orders, but these essentially are exchanges between investors not governed by the NYSE or Nasdaq and not reported on their trade information systems. The Consolidated Tape Association, the central distributor of transaction information on exchange-traded issues, established 4 p.m. as the closing time. Nasdaq observes the same close.
Extended-hour trades are reported with a "t" tag and do not affect the closing prices reported in daily summaries provided by the market operators or the daily high and low ranges in reports or stock tables published in newspapers and other outlets. The 4 p.m. close also is used by mutual funds to calculate their net asset value, which is reported daily to the Securities and Exchange Commission.
The closing price of a stock is that of the last trade of a day, as of the 4 p.m. end of regular trading. It typically is the next to last column in a stock market table, following the name of the issue, its volume or total sales for the day and perhaps a price/earnings ratio or high/low comparison. It is used to figure the change or comparison with the last trade of the previous session.
Some market data vendors and individual companies may display a closing price based on extended or after-hours trading. Nasdaq compiles an "after-hours indicator," but it is based on only 100 issues and does not report all trades. An investor who sees a discrepancy in closing prices between two sources should check the end-of-day price on the security's primary market, which will be based on a 4 p.m. close. The only stocks not affected by those hours are unlisted issues called over the counter stocks.
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