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.
While JB King says some useful things, I think there is another fundamental reason why stock markets go down after disasters, either natural or man-made.  There is a real impact on the markets - in the case of something like 9/11 due to closed airport, higher security costs, closer inspections on trade goods, tighter restrictions on visas, real payments for the rebuilding of destroyed buildings and insurance payouts for killed people, and eventually the cost of a war. But almost as important is the uncertainty and risk. Nobody knew what was going to happen in the days and weeks after an attack like that. Is there going to be another one a week later, or every week for the next year? Will air travel become essentially impractical? Will international trade be severely restricted? All those would have a huge, massive effect on the economy. You may argue that those things are very unlikely, even after something like 9/11. But even a small increase in the likelihood of a catastrophic economic crash is enough to start people selling. There is another thing that drives the market down. Even if most people are sure that there won't be a catastrophic economic crash, they know that other people think there might be and so will sell. That will drive the market down. If they know the market is going down, then sensible traders will start to sell, even if they think there is zero risk of a crash. This makes the effect worse. Eventually prices will drop so far that the people who don't think there is a crash will start to buy, so they can make a profit on the recovery. But that usually doesn't happen until there has been a substantial drop. I think we are just close to  point where there are so many people working in the job market that youre not going to have any more hiring going forward. Trump had some hype when he came into office that rippled onto the market resulting in these stock market gains and then the job growth as the after effect. but now that is finished. the stock market is at huge valuations, and its hard to see increases in corporate profits from here (given that the credit market is going to cut down the supply of loans going forward)  that could spark another hiring rally. &gt;As a boston resident, these stores will be jam packed this weekend. The store i go to has 20 lanes 5-6 customers deep from opening on friday to close, and it looks like that almost every weekend day.   Which is one of the top criticisms of Market Basket.  If they are smart, they will overstaff this weekend as they have a chance for new customers.  If there are 15-minute waits to checkout, they won't win over new customers at all.  MB shoppers are slightly lower SES than the overall population, but that is primarily due to the lower prices.    We'll see what their weekly sales look like for the upcoming months, and I won't be shocked to see a slight change from where it was previously, be that higher or lower. In less than two decades, more than half of all publicly traded companies have disappeared. There were 7,355 U.S. stocks in November 1997, according to the Center for Research in Security Prices at the University of Chicago’s Booth School of Business. Nowadays, there are fewer than 3,600.  A close look at the data helps explain why stock pickers have been underperforming. And the shrinking number of companies should make all investors more skeptical about the market-beating claims of recently trendy strategies.  Back in November 1997, there were more than 2,500 small stocks and nearly 4,000 tiny “microcap” stocks, according to CRSP. At the end of 2016, fewer than 1,200 small and just under 1,900 microcap stocks were left.  Most of those companies melted away between 2000 and 2012, but the numbers so far show no signs of recovering.  Several factors explain the shrinking number of stocks, analysts say, including the regulatory red tape that discourages smaller companies from going and staying public; the flood of venture-capital funding that enables young companies to stay private longer; and the rise of private-equity funds, whose buyouts take shares off the public market.  For stock pickers, differentiating among the remaining choices is “an even harder game” than it was when the market consisted of twice as many companies, says Michael Mauboussin, an investment strategist at Credit Suisse in New York who wrote a report this spring titled “The Incredible Shrinking Universe of Stocks.”  That’s because the surviving companies tend to be “fewer, bigger, older, more profitable and easier to analyze,” he says — making stock picking much more competitive.  Consider small-stock funds. Often, they compare themselves to the Russell 2000, an index of the U.S. stocks ranked 1,001 through 3,000 by total market value. “Twenty years ago, there were over 4,000 stocks smaller” than the inclusion cutoff for the Russell 2000, says Lubos Pastor, a finance professor at the University of Chicago. “That number is down to less than 1,000 today.”  So fund managers have far fewer stocks to choose from if they venture outside the index — the very area where the best bargains might be found. More money chasing fewer stocks could lead some fund managers to buy indiscriminately, regardless of value.  Eric Cinnamond is a veteran portfolio manager with a solid record of investing in small stocks. Last year, he took the drastic step of shutting down his roughly $400 million mutual fund, Aston/River Road Independent Value, and giving his investors their money back.  “Prices got so crazy in small caps, I fired myself,” he says. “My portfolio was 90% in cash at the end, because I couldn’t find anything to buy. If I’d kept investing, I was sure I’d lose people their money.”  He adds, “It was the hardest thing I’ve ever done professionally, but I didn’t feel I had a choice. I knew my companies were overvalued.”  Mr. Cinnamond hopes to return to the market when, in his view, values become attractive again. He doesn’t expect recent conditions to be permanent.  The evaporation of thousands of companies may have one enduring result, however — and it could catch many investors by surprise.  Most research on historical returns, points out Mr. Mauboussin, is based on the days when the stock market had twice as many companies as it does today. “Was the population of companies so different then,” he asks, “that the inferences we draw from it might no longer be valid?”  So-called factor investing, also known as systematic or smart-beta investing, picks hundreds or thousands of stocks at a time based on common sources of risk and return. Among them: how big companies are, how much their shares fluctuate, how expensive their shares are relative to asset value and so on.  But the historical outperformance of many such factors may have been driven largely by the tiniest companies — exactly those that have disappeared from the market in droves.  Before concluding that small stocks or cheap “value” stocks will outrace the market as impressively as they did in the past, you should pause to consider how they will perform without the tailwinds from thousands of tiny stocks that no longer exist.  The stock market has more than tripled in the past eight years, so the eclipse of so many companies hasn’t been a catastrophe. But it does imply that investing in some of the market’s trendiest strategies might be less profitable in the future than they looked in the past. "Well, it's not even just about dealing with a half day. There is literally a message on every single data feed that states ""this is it for this trading session"". Why the hell would you consider any data after that as something you'd process?" The root cause can be said to always be a crisis in confidence.  It may be due to a very real event.  However, confidence is what pushes the markets up and worries are what bring them down. "Part of it was an Oops, but not all of it. There were reports that the sudden   drop was caused by a trader who   mistyped an order to sell a large   block of stock. The drop in that   stock's price was enough to trigger   ""sell"" orders across the market. Source: http://www.msnbc.msn.com/id/36983596/ns/business-stocks_and_economy/" "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."