Why is the stock market closed on the weekend?
While a lot of trading is executed by computers, a substantial amount is still done at the behest of humans.  Brokers managing accounts, Portfolio Managers, and Managers of Mutual Funds doing stock picks etc.  Those folks are still initiating a very large number of the trades (or at least one side of a trade).  And those humans don't work 7 days a week. it's not just computers talking to computers at the behest of other computers.  And even a lot of places that use computers to create models and such, there are still humans in the loop to ensure that the computers are not ordering something stupid to be done. I personally worked for a firm that managed nearly $20Billion in stock portfolios.  The portfolios were designed to track indexes, or a mix of indexes and actively managed funds, but with the addition of managing for tax efficiency.  A lot of complex math and complicated 'solver' programs that figured out each day what if anything to trade in each portfolio.  Despite all those computers, humans still reviewed all the trades to be sure they made sense. And those humans only worked 5 days a week. After-hours trading and alternate venues allow one to trade outside of regular market hours. However there are a few reasons why you would not want to: The purpose of an exchange is to improve liquidity by gathering all buyers and sellers in the same place at the same time. If trading was 24/7, not all market participants would be trading at the same time. Some markets (including NASDAQ) depend on market makers or specialists to help liquidity. These exchanges are able to mandate that the market maker actively make a market in a security during a meaningful percentage of the trading day. Requiring 24/7 active market making may not be reasonable. Trading systems, meaning both exchange infrastructure and market participant infrastructure, need maintenance time. It's nice to have the evenings and weekends for scheduled work. Post-trade clearing and settlement procedures are still somewhat manual at times. You need staff around to handle these processes. The answer is 7-fold:   BOTTOM LINES: Bubble; bursting bubble; Great Depression; Victory in WWII; All work and no play makes Jack (& Jill) very dull persons. The stock markets are closed on week-ends and public holidays because the Banks are closed. The Banking is a must to settle the payment obligations. So you may buy and sell as much as you wish, but unless money changes hands, nothing has really happened.   Now as to why Banking itself is closed on week-ends and public holidays, well a different question :) Keeping the system 24 hrs up and running does not actually push volumes, but definately push expenses for brokers, Banks etc. There definately is some convinience to buyers and sellers. There are a number of factors here. 1) It's important that there is human oversight on the system. At one level someone needs to be monitoring the computers that manage the trading to be sure they are functioning. At another level someone needs to be making judgement calls on important but rare events: when you you suspend trading in a stock? When do you close the stock exchange entirely? It is alleged that unsupervised computer trades were at least partly responsible for the May 2010 selloff. Even if that's unproven, would you really want those unsupervised computers trading with each other for a couple of days? Or even for a couple of hours? 2) Providing 24/7 trading would increase the cost of running a stock exchange, but with only a tiny improvement in liquidity. 3) If the stock exchange ran 24/7 then traders would have to run 24/7. That would add hugely to the cost of trading. 4) The people who would really suffer would be day traders - because there would no longer be such a thing as a day trader. If you were a sole trader then you would need to monitor your investments 24/7, or risk waking up in the morning to find one of your stocks had plummeted overnight. Simply, most of the above given 'answers' are mere 'justifications' for a practice that has become anachronistic. It did make sense once in the past, but not any more. Computers and networks can run non-stop 24/7; even though the same human beings cannot be expected to work 24/7, we have invented the beautiful concept of multiple shifts; banks may be closed during nights and weekends, but banking is never closed in the internet era; ...The answer must lie in the vested interests of a few stakeholder groups - or - it could just be our difficult to change habits.
I've never seen a dividend, split or other corporate action during the day, but I have seen trade suspended a few times when something big happened. The market opening price is not in general the same as the close of the previous day. It can gap up or down and does frequently. I don't know of an api to find out if the dividend was cash or stock, but stock dividends are a lot less common. "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." It is because 17th was Friday, 18th-19th were weekends and 20th was a holiday on the Toronto Stock Exchange (Family Day). Just to confirm you could have picked up another stock trading on TMX and observed the price movements. First - Google's snapshot -  Then - Yahoo -  I took these snapshots because they will not exist on line after the market opens, and without this context, your question won't make sense. With the two snapshots you can see, Yahoo shows the after hours trades and not just the official market close for the day. The amount it's down is exactly tracked from the close shown on Google. Now you know. It is called the Monday Effect or the Weekend Effect. There are a number of similar theories including the October Effect and January Effect. It's all pretty much bunk. If there were any truth to traders would be all over it and the resulting market forces would wipe it out. Personally, I think all technical analysis has very little value other than to fuel conversations at dinner parties about investments. You might also consider reading about Market efficiency to see further discussion about why technical approaches like this might, but probably don't work. Most stocks are not actively trades by lots of people.   When you buy or sell a stock the price is set by the “order book” – that is the other people looking to trade in the given stock at the same time. Without a large number of active traders, it is very likely the pricing system will break down and result in widely changing prices second by second.   Therefore for the market to work well, it need most people to be trading at the same time. There's something very important no one else has mentioned... times when the stock market falls dramatically are often the times when you're most likely to lose your job, and when it's hardest to get loans.  So if you ever do need your emergency fund, it will more than likely be related to a dip in the stock market. During the 12 plus hours the market was closed news can change investors opinion of the stock. When the market reopens that first trade could be much different than the last trade the day before. The two answers so far are right, but there's a third factor - for many stocks, there's after hours trading. So the official 4PM close is not what the stock's last trade was when they open again. Regardless, even that after hour price is not the starting point as Muro points out. 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: 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. Summarized article: On Friday, the Dow Jones Industrial Average dropped almost 275 points and wiped out the last of the index's gains for the year.   Friday's massive selloff was triggered by a dismal US jobs report and data indicating a European and Chinese economic slowdown. Friday was the worst day of the year for the market.   Worried investors moved cash to the US Treasury bond market which also dragged the yield to a record low.   Some analysts believe the panic in the market may cause the Federal Reserve to plan for additional stimulus.   Federal Reserve Chairman Ben Bernanke is scheduled to speak next week.   *For more summarized news, subscribe to the [/r/SkimThat](http://www.reddit.com/r/SkimThat) subreddit* Many of the major indices retreated   today because of this news. Why? How   do the rising budget deficits and debt   relate to the stock markets? The major reason for the market retreating is the uncertainty regarding the US Dollar. If the US credit rating drops that will have an inflationary effect on the currency (as it will push up the cost of US Treasuries and reduce confidence in the USD). If this continues the loss of USD confidence could bring an end to the USD as the world's reserve currency which could also create inflation (as world banks could reduce their USD reserves). This can make US assets appear overvalued. Why is there such a large emphasis on   the S&P rating? S&P is a large trusted rating agency so the market will respond to their analysis much like how a bank would respond to any change in your rating by Transunion (Consumer Credit Bureau) Does this have any major implications   for the US stock markets today, in the   short term and in July? If you are a day-trader I'm sure it does. There will be minor fluctuations in the market as soon as news comes out (either of its extension or any expected delays in passing that extension). What happens when the debt ceiling is   reached? Since the US is in a deficit spending situation it needs to borrow more to satisfy its existing obligations (in short it pays its debt with more debt). As a result, if the debt ceiling isn't raised then eventually the US will be unable to pay its existing obligations. We would be in a default situation which could have devastating affects on the value of the USD. How hard the hit will depend on how long the default situation lasts (the longer we go without an increased ceiling after the exhaustion point the more we default on). In reality, Congress will approve a raise, but they will drag it out to the last possible minute. They want to appear as if they are against it, but they understand the catastrophic effects of not doing so. In general a stock can open at absolutely any price with no regard for the closing price or after hours price the previous day. The opening price will be determined by the best bid and offer made by people who decide to trade the next day.  Some of the those people may have put orders in on a prior day that are still on the books and matter, but there's a lot of time overnight for people to cancel orders and enter new ones, which is especially likely to happen if there was substantive news overnight. As for what you can do in your case, you have the same options that you always had:  Sell or hold.  If you're selling, you can sell after hours, in the pre-open hours, or during the trading day.  There's nothing we can say about this case that's really any different than we can say about any other stock on any other day. "US law dictates that you cannot buy / sell shares in a company you   work for except during open trading windows. I understand lockout   periods when you're in a company but what about after you quit? There's no such law. Trading lockouts are imposed by companies themselves to avoid the complexities of identifying ""insiders"". For large companies it sometimes is easier/cheaper to assume everyone is insider instead of imposing internal data flow controls and limitations. For such companies, their internal policies would also manage how the employees who are leaving should be treated."