For what dates are the NYSE and U.S. stock exchanges typically closed?
The NYSE publishes a list of holidays at its website.  New link: https://www.nyse.com/markets/hours-calendars Old link in the original answer that doesn't work now: http://www.nyse.com/about/newsevents/1176373643795.html Hope that helps! Stumbled upon this question, I've found the updated dates for 2016 and 2017 in a more permanent location. https://www.nyse.com/markets/hours-calendars "All public US equity exchanges are closed on the 9 US trading holidays (see below) and open on all other days.  Exchanges also close early (13:00 ET) on the Friday after Thanksgiving and on the day before Independence Day if Independence Day is being observed on a Tuesday, Wednesday, Thursday, or Friday.  (Some venues have extended trading hours as a matter of course; for them an ""early close"" might be later than 13:00 ET.) To answer the second question, yes, if you know NASDAQ's or AMEX's holiday schedule, then you know NYSE's (modulo the timing of their early close).  I'm not sure about the options exchanges; they're not regulated the same way and are a good example of exchanges with extended trading hours in the first place. The US trading holidays are as follows.  Note that trading holidays are not the same as federal or bank holidays, which include Columbus Day and Veterans Day but do not include Good Friday."
Is it possible that mutual funds account for a significant portion of this volume. Investors may decide to buy or sell anytime within a 24 hour period, but the transaction only happened at the close of the market. Therefore at 3:59 pm the mutual fund knows if they will be buying or selling stocks that day.  As nws pointed out the non-market hours are longer and therefore accumulate more news event. Some financial news is specifically given during the time the market is closed. Therefore the reaction to that news has to either be in the morning when the market opens or in the late afternoon if they are trying to anticipate the news.  Also in the US market the early morning trader may be reacting to European market activities. The NYSE is not the only exchange in the world (or even the only one in the USA). Amazingly, the London stock exchange works on London time, the Shanghai exchange works on Shanghai time and the Australian stock exchange works on Sydney time. In addition futures exchanges work overnight. There are several reasons why this may happen and I will update as I get more information from you. Volumes on that stock look low (supposing that they are either in a factor between 1s and 1000s) so it could well be that there was no volume on that day. If no trades occur then open, high and low are meaningless as they are statistics based on trades that occur that day and no trades occur. Remember that there has to be volume to get a price. The stock may have been frozen by either the exchange or the company for the day. This could be for various reasons including to prevent some illegal activity. In that case no trades were made because the market for that stock was closed. Another possibility is that all trades that day were cancelled by the exchange. The exchange may cancel all trades if there is unusual, potentially fraudulent or other illegal activity on the stock. In this case the last price for that day existed but was rolled back by the exchange and never occurred. This is a rare situation. Although I can't find any holidays on that date it is possible that this is how your data provider marks market holidays. It would be valid to ignore the data in that case as being from a non-market day. I cannot tell if this is possible without knowing exchange information. There is a possibility that some data providers don't receive data for a day or that it gets corrupted. It may be worth checking another source to ensure the integrity of the data that you are receiving. Whichever reason is true, the data provider has made the close equal to the previous day's close as no price movements occurred. Strictly the closing price is the price of the last trade made for that day and so should be null (and open, high and low should be null too and not 0 otherwise the price change on day is very large!). Therefore, to keep integrity, you have a few choices: You can find the NYSE holiday dates listed on the exchange's own site (already linked in answer above), which should obviously be consulted as the most reliable source; they are also published in an article that I have written here: NYSE Holidays 2016, which provides additional information about traditions and events that can be expected to lead to unscheduled closures, and closed dates for holidays that are day-of-month rather than date specific (e.g. President's Day and Memorial Day). NYSE Holidays are not quite identical to those for the Chicago Mercantile Exchange, though most US stock exchange dates are the same. Also, note that both the Merc (via the Globex platform) and NYSE Arca have different normal cash sessions and trading hours to the New York Stock Exchange. "The third Friday of each month is an expiration for the monthly options on each stock.  Stock with standardized options are in one of three ""cycles"" and have four open months at any give time.  See http://www.investopedia.com/terms/o/optioncycle.asp In addition some stocks have weekly options now.  Those generally have less interest because they are necessarily short-term.  Anything expiring on April 8 and 22 (Fridays this year but not third Fridays of the month) are weeklies. The monthly options are open for longer periods of time so they attract more interest over the time that they are open.  They also potentially attract a different type of investor due to their length of term, although, as it gets close to their expiration date they may start to behave more like weeklies." Your order may or may not be executed.  The price of stock can open anywhere.  Often yesterday's close is a good indication of today's open, but with a big event overnight, the open may be somewhere quite different.  You'll have to wait and see like the rest of us.  Also, even if it doesn't execute at the open, the price could vary during the day and it might execute later. Opened Long - is when you open a long position. Long means that you buy to open the position, so you are trying to profit as the price rises. So if you were closing a long position you would sell it. Closed Short - is when you close out a short position. Short means that you sell to open and buy back to close. With a short position you are trying to profit as the price falls. Scaled Out - means you get out of a position in increments as the price climbs (for long positions). Scaled In - means you set a target price and then invest in increments as the stock falls below that price (for long positions). How come when I sell stocks, the brokerage won't let me cash out for three days, telling me the SEC requires this clearance period for the transaction to clear, but they can swap shit around in under a second?   Be interesting to see what would happen if *every* transaction wasn't cleared until the closing bell. What typically happens to brokerage accounts during similar situations? This depends on country, time and situation. Nothing is predictable in such situations. In Greece during the said period the stock exchanges were closed for 5 weeks. There was no trading.  Edits: Every situation is different and it would be unfair to compare one against another or use it to predict something else. Right now in India due to demonitization, cash withdrawal is limited. One can trade in stocks, unlimited bank transfers, transfer money out of India ...etc. Everything same except for cash withdrawal. In 1990, the ASEAN countries survived a financial collapse, everything was allowed except moving money out of country. http://www.marketwatch.com/optionscenter/calendar would note some options expiration this week that may be a clue as this would be the typical end of quarter stuff so I suspect it may happen each quarter. http://www.investopedia.com/terms/t/triplewitchinghour.asp would note in part: Triple witching occurs when the contracts for stock index futures,   stock index options and stock options expire on the same day. Triple   witching days happen four times a year on the third Friday of March,   June, September and December. Triple witching days, particularly the   final hour of trading preceding the closing bell, can result in   escalated trading activity and volatility as traders close, roll out   or offset their expiring positions. June 17 would be the 3rd Friday as the 3rd and 10th were the previous two in the month. One of the fundamental of technical analysis suggests that holding a security overnight represents a huge commitment.  Therefore it would follow that traders would tend to close their positions prior to market close and open them when it opens. "You cannot determine this solely by the ticker length. However, there are some conventions that may help steer you there. Nasdaq has 2-4 base letters BATS has 4 base letters NYSE equity securities have 1-4 base letters. NYSE Mkt (formerly Amex) have 1-4 base letters. NYSE Arca has 4 base letters OTC has 4 base letters. Security types other than equities may have additional letters added, and each exchange (and data vendors) have different conventions for how this is handled. So if you see ""T"" for a US-listed security it would be only be either NASDAQ, NYSE or NYSE Mkt. If you see ""ANET"" then you cannot tell which exchange it is listed on.  (In this case, ANET Arista Networks is actually a NYSE stock). For some non-equity security types, such as hybrids, and debt instruments, some exchanges add ""P"" to the end for ""preferreds"" (Nasdaq and OTC) and NYSE/NYSE Mkt have a variety of methods (including not adding anything) to the ticker.  Examples include NYSE:TFG, NYSEMkt:IPB, Nasdaaq: AGNCP, Nasdaq:OXLCN.  It all becomes rather confusing given the changes in conventions over the years. Essentially, you require data that provides you with ticker, listing location and security type. The exchanges allocate security tickers in conjunction with the SEC so there are no overlaps.  eg. The same ticker cannot represent two different securities. However, tickers can be re-used.  For example, the ticker AB has been used by the following companies:" "Prices reflect all available information. (Efficient markets hypothesis) A lot can happen between the time a stock closes on one day and opens on another. Particularly in a heavily traded stock such as IBM. Basically, you have a different ""information set"" the following day, which implies a different price. The instances where you are most likely to have a stock where the price opens at the same price is at the previous close is a thinly traded stock on which you have little information, meaning that the ""information set"" changes less from day to day." For exchange contracts, yes. A trader can close a position by taking an offsetting position. CME's introduction to Futures explains it quite well (on page 22).  Exiting the Market Jack entered the market on the buy side,   speculating that the S&P 500 futures price would move higher. He has   three choices for exiting the market: "During the day, market and limit orders are submitted at any time by market participants and there is a bid and an ask that move around over time.  Trades occur whenever a market order is submitted or a limit order is submitted that at a price that matches or exceeds an existing limit order.  If you submit a market order, it may consume all best-price limit orders and you can get multiple prices, changing the bid or ask at the same time.  All that stuff happens during the trading day only. What happens at the end of the day is different.  A bunch of orders that were submitted during the day but marked as ""on close"" are aggregated with any outstanding limit orders to create a single closing price according to the algorithm established by the exchange.  Each exchange may handle the details of this closing event differently.  For example, the Nasdaq's closing cross or the NYSE's closing auction. The close is the most liquid time of the day, so investors who are trading large amounts and not interested in intraday swings will often submit a market-on-close or limit-on-close order.  This minimizes their chance of affecting the price or crossing a big spread.  It's actually most relevant for smaller stocks, which may have too little volume during the day to make big trades, but have plenty at the close.  In short, the volume you see is due to these on-close orders. The spike in volume most likely has no special information about what will happen overnight or the next day.  It's probably just a normal part of the market for illiquid stocks."