In the stock market, why is the “open” price value never the same as previous day's “close”?
"What most of these answers here seem to be missing is that a stock ""price"" is not exactly what we typically expect a price to be--for example, when we go in to the supermarket and see that the price of a gallon of milk is $2.00, we know that when we go to the cash register that is exactly how much we will pay.  This is not, however, the case for stocks. For stocks, when most people talk about the price or quote, they are really referring to the last price at which that stock traded--which unlike for a gallon of milk at the supermarket, is no guarantee of what the next stock price will be.  Relatively speaking, most stocks are extremely liquid, so they will react to any information which the ""market"" believes has a bearing on the value of their underlying asset almost (if not) immediately.  As an extreme example, if allegations of accounting fraud for a particular company whose stock is trading at $40 come out mid-session, there will not be a gradual decline in the price ($40 -> $39.99 -> $39.97, etc.)-- instead, the price will jump from $40 to say, $20.  In the time between the the $40 trade and the $20 trade, even though we may say the price of the stock was $40, that quote was actually a terrible estimate of the stock's current (post-fraud announcement) price. Considering that the ""price"" of a stock typically does not remain constant even in the span of a few seconds to a few minutes, it should not be hard to believe that this price will not remain constant over the 17.5 hour period from the previous day's close to the current day's open.  Don't forget that as Americans go to bed, the Asian markets are just opening, and by the time US markets have opened, it is already past 2PM in London.  In addition to the information (and therefore new knowledge) gained from these foreign markets' movements, macro factors can also play an important part in a security's price-- perhaps the ECB makes a morning statement that is interpreted as negative news for the markets or a foreign government before the US markets open.  Stock prices on the NYSE, NASDAQ, etc. won't be able to react until 9:30, but the $40 price of the last trade of a broad market ETF at 4PM yesterday probably isn't looking so hot at 6:30 this morning... don't forget either that most individual stocks are correlated with the movement of the broader market, so even news that is not specific to a given security will in all likelihood still have an impact on that security's price. The above are only a few of many examples of things that can impact a stock's valuation between close and open: all sorts of geopolitical events, announcements from large, multi-national companies, macroeconomic stats such as unemployment rates, etc. announced in foreign countries can all play a role in affecting a security's price overnight. As an aside, one of the answers mentioned after hours trading as a reason--in actuality this typically has very little (if any) impact on the next day's prices and is often referred to as ""amateur hour"", due to the fact that trading during this time typically consists of small-time investors.  Prices in AH are very poor predictors of a stock's price at open." Quoted from money.howstuffworks.com: NASDAQ has come up with an auction approach called the opening cross. Here's how it works. In the morning, a computer program looks at all the orders that have come in overnight in each different stock. Based on those orders, the program picks a price level that would be the best opening price. However, it also looks to see if there's a trade imbalance. For example, if a company announced bad news after the market closed, there might be 10 times more sell orders than buy orders. NASDAQ then broadcasts the price and imbalance information to its network of dealers with the goal of offsetting the imbalance. It then lets dealers place orders. This all happens very quickly, in a time window of two minutes or so, right before the market opens. Dealers can place orders, and those orders are factored into the opening price. Further reading here: Opening Price calculation A stock's price does not move in a completely continuous fashion.  It moves in discrete steps depending on who is buying/selling at given prices. I'm guessing that by opening bell the price for buying/selling a particular stock has changed based on information obtained overnight. A company's stock closes at $40.  Overnight, news breaks that the company's top selling product has a massive defect.  The next morning the market opens.  Are there any buyers of the stock at $40?  Probably not.  The first trade of the stock takes place at $30 and is thus, not the same as the previous day's close. It's done by Opening Auction (http://www.advfn.com/Help/the-opening-auction-68.html): The Opening Auction Between 07.50 and   a random time between 08.00 and   08.00.30, there will be called an auction period during which time,   limit and market orders are entered   and deleted on the order book. No   order execution takes place during   this period so it is possible that the   order book will become crossed. This   means that some buy and sell orders   may be at the same price and some buy   orders may be at higher prices than   some sell orders. At the end of the random start period,   the order book is frozen temporarily   and an order matching algorithm is   run. This calculates the price at   which the maximum volume of shares in   each security can be traded. All   orders that can be executed at this   price will be filled automatically,   subject to price and priorities. No   additional orders can be added or   deleted until the auction matching   process has been completed. The opening price for each stock will   be either a 'UT' price or, in the   event that there are no transactions   resulting form the auction, then the   first 'AT' trade will be used. The simple answer: The opening price is the price of the first trade of the day and the closing price is the price of the last trade of the day.  And since the stock price change from trade to trade they are usually different. 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. Besides overnight news events and auction mechanisms there is a more fundamental reason the price of a stock is always moving.  Theoretically the stock price will move slightly even in the unlikely scenario that absolutely nothing of interest happens during the entire night.  Let me go into that in some more detail: Stock valuation using Discounted Cash FLow One of the fundamental reasons that stock value is constantly changing is because underneath every stock there is a company that expects to make some kind of profit or loss in the future. We have to go into the fundamentals of stock value to understand why this is important: One popular way to determine the value of a stock is by looking into the future and summing up all the earnings (or cashflows) it has yet to produce. You have to reduce each amount by a certain factor that gets larger for payments that are farther into the future. Think of it this way: a dollar in hand now is better than a dollar that you get tomorrow. This method of valuation is called Discounted Cash Flow (abbr. DCF; see the wikipedia article on DCF) Time's effect on stock value Now take the Close price C, and the open price O. Let's assume that since there has been no news, the expectations for future earnings are the same for C and O. Remember that the discounting factor for these earnings is dependent on the time until the cashflow occurs? For O, this time is slightly shorter than for C, and therefore the value will be slightly higher (or lower, when the company is expected to incur losses). So now you can see that even without all the external forces that continuously push and pull on the stock price, a stock still changes in value over time. Hope this helps. "It's almost like why don't you wake up in the morning feeling exactly like you slept the earlier night? yeah, once in a while that'll happen, but it's not designed to be that way. Stuff happens. The close of the stock is what happened at 4 PM (for US stocks). The ""open"" is simply the first price ever, or an open price auction like NimChimpsky said. Most things that trade have an open/close cycle, even what seemingly trades all the time (some markets trade 23 hours). Forex trades in different exchanges which have overlapping timing but each market will have an open, high, low and close for each day - for what is the same underlying currency. Also, it's not exactly true that close<>open. Take the GS chart, Oct 1 2010 and Oct 4 2010 (there was a weekend in between). The Oct 1 close was the same as the Oct 4 open. Note that Oct 4 was a down day so it's in red - the open is the upper end of the body (not including the wick), and Oct 1 was an up day so its close was the upper end too. (Candles are drawn so that the open ends of the wicks are the High and Low of the period respectively, and the lower end of the body is the open if it was an up-day, meaning the stock closed higher than it opened, and the body in coloured green below. If the stock went down that day from the open, the body's in red and the lower end is the close. Vice-versa for the other end)  The way to get to this: Go to yahoo finance, choose a stock, go to historical prices, click download data (you should have about 10 years of data), paste into excel, insert a formula to check if prev day's close = current day's open, and I'm sure you'll see at least one instance per stock." It does sometimes open one day the same as it closed the previous day.  Take a look at ESCA, it closed October 29th at 4.50, at opened November 1st at 4.50.  It's more likely to change prices overnight than it is between two successive ticks during the day, because a lot more time passes, in which news can come out, and in which people can reevaluate the stock. "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." "Nobody has mentioned the futures market yet. Although the stock market closes at 4pm, the futures market continues trading 24 hours a day and 5.5 days a week. Amongst the products that trade in the future market are stock index futures.  That includes the Dow Jones, the S&P 500. These are weighted averages of stocks and their sectors. You would think that the price of the underlying stock dictates the price of the average, but in this day and age, the derivative actually changes the value of the underlying stock due to a very complex combination of hedging practices. (this isn't meant to be vague and mysterious, it is ""delta hedging"") So normal market fluctuations coupled with macroeconomic events affect the futures market, which can ripple down to individual stocks. Very popular stocks with large market caps will most certainly be affected by futures market trading. But it is also worth mentioning that futures can function completely independently of a ""spot"" price. This is where things start to get complicated and long winded. The futures market factor is worth mentioning because it extends even outside of the aftermarket and pre-market hours of stock trading." A stock is only worth what someone is willing to pay for it. If it trades different values on different days, that means someone was willing to pay a higher price OR someone was willing to sell at a lower price.  There is no rule to prevent a stock from trading at $10 and then $100 the very next trade... or $1 the very next trade. (Though exchanges or regulators may halt trading, cancel trades, or impose limits on large price movements as they deem necessary, but this is beside the point I'm trying to illustrate). Asking what happens from the close of one day to the open of the next is like asking what happens from one trade to the next trade... someone simply decided to sell or pay a different price.  Nothing needs to have happened in between.
Firstly what are you trading that you could lose more than you put in? If you are simply trading stocks you will not lose more than you put in, unless you are trading on margin. A limit order is basically that, a limit on the maximum price you want your buy order bought at or the minimum price you want your sell order sold at. If you can't be glued to the screen all day when you place a limit order, and the market moves the opposite way, you may miss out on your order being executed. Even if you can be in front of the screen all day, you then have to decide if you want to chase the market of miss out on your purchase or sale. For example, if a stock is trading at $10.10 and you put a limit buy order to buy 1000 shares at or below $10.00 and the price keeps moving up to $10.20, then $10.30 and then $10.50, until it closes the day at $11.00. You then have the choice during the day to miss out on buying the shares or to increase your limit order in order to buy at a higher price. Sometime if the stock is not very liquid, i.e. it does not trade very often and has low volume, the price may hit $10.00 and you may only have part of your order executed, say 500 out of your 1000 shares were bought. This may mean that you may have to increase the price of your remaining order or be happy with only buying 500 shares instead of 1000. The same can happen when you are selling (but in reverse obviously). With market order, however, you are placing a buy order to buy at the next bid price in the depth or a sell order to sell at the next offer price in the depth. See the market depth table below:  Note that this price depth table is taken before market open so it seems that the stock is somewhat illiquid with a large gap between the first and second prices in the buyers (bid) prices. When the market opened this gap is closed, as WBC is a major Australian bank and is quite liquid. (the table is for demonstration purposes only). If we pretend that the market was currently open and saw the current market depth for WBC as above, you could decide to place a limit sell order to sell 1000 shares at say $29.91. You would sell 100 shares straight away but your remaining 900 sell order will remain at the top of the Sellers list. If other Buyers come in at $29.91 you may get your whole sale completed, however, if no other Buyers place orders above $29.80 and other Sellers come into the market with sell orders below $29.91, your remaining order may never be executed. If instead you placed a market sell order you would immediately sell 100 shares at $29.91 and the remaining 900 shares at $29.80. (so you would be $99 or just over 0.3% worse off than if you were able to sell the full 1000 shares at $29.91). The question is how low would you have had to lower your limit order price if the price for WBC kept on falling and you had to sell that day? There are risks with whichever type of order you use. You need to determine what the purpose of your order is. Is it to get in or out of the market as soon as possible with the possibility of giving a little bit back to the market? Or is it to get the price you want no matter how long it takes you? That is you are willing to miss out on buying the shares (can miss out on a good buy if the price keeps rising for weeks or months or even years) or you are willing to miss out on selling them right now and can wait for the price to come back up to the price you were willing to sell at (where you may miss out on selling the shares at a good price and they keep on falling and you give back all your profits and more). Just before the onset of the GFC I sold some shares (which I had bought a few years earlier at $3.40) through a market order for $5.96. It had traded just above $6 a few days earlier, but if instead of a market order I had placed a limit order to sell at $6.00 or more I would have missed out on the sale. The price never went back up  to $6 or above, and the following week it started dropping very quickly. It is now trading at about $1.30 and has never gone back above $2.00 (5.5 years later). So to me placing a limit order in this case was very risky. Does the price only start the day based on the previous day's rebalancing? No, the tracker will open at the price according to the stock it is tracking.  So for example, if the ETF closed at $10 but the tracked stock continued trading and was priced $15 when the ETF reopened the ETF will open at $15. (Example is for a non-leveraged ETF.) "In the US, stocks are listed on one exchange but can be traded on multiple venues.  You need to confirm exactly what your data is showing: a) trades on the primary-listed exchange; or b) trades made at any venue. Also, the trade condition codes are important.  Only certain trade condition codes contribute towards the day's open/high/low/close and some others only contribute towards the volume data.  The Consolidated Tape Association is very clear on which trades should contribute towards each value - but some vendors have their own interpretation (or just simply an erroneous interpretation of the specifications). It may surprise you to find that the majority of trading volume for many stocks is not on their primary-listed exchange.  For example, on 2 Mar 2015, NASDAQ:AAPL traded a total volume across all venues was 48096663 shares but trading on NASDAQ itself was 12050277 shares. Trades can be cancelled.  Some data vendors do not modify their data to reflect these busted trades.   Some data vendors also ""snapshot"" their feed at a particular point in time of the data.  Some exchanges can provide data (mainly corrections) 4-5 hours after the closing bell.  By snapshotting the data too early and throwing away any subsequent data is a typical cause of data discrepancies.   Some data vendors also round prices/volumes - but stocks don't just trade to two decimal places. So you may well be comparing two different sets of trades (with their own specific inclusion rules) against the same stock.  You need to confirm with your data sources exactly how they do things. Disclosure: Premium Data is an end-of-day daily data vendor." The sentiment is because between closing and opening a lot can happen, and between opening and the time your order actually goes through, even more can happen.  An after-hours trade has an extra amount of short-term risk attached; the price of a stock at the opening bell is technically the same as its price as of the closing the previous trading day, but within a tenth of a second, which is forever in a computerized exchange, that price may move drastically one way or the other, based on news and on other markets. The sentiment, therefore, is simple; if you're trading after-hours, you're trading risky. You're not trading based on what the market's actually doing, you're trading based on what you think the market will do in the morning, and there's still more math going on every second in the privately-held supercomputers in rented cubes in the NYSE basement than you could do all night, digesting this news and projecting what it's going to do to the stocks. Now, if you've done your homework and the stock looks like a good long-term buy, with or without any after-hours news, then place the order at 3 in the morning; who cares what the stock's gonna do at the opening bell. You're gonna hold that stock for the next ten years, maybe; what it does in 5 seconds of opening turmoil is relatively minor compared to the monthly trends that you should be worrying about. 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. Consider the mechanic which actually drives the 'price' of a stock. In simplest terms, the 'price' of a stock is the price at which the most recent trade occurred. ie: if the price of IBM is $100/share, that means the last time someone bought IBM stock, they paid $100. Above and below the 'spot price', are dozens/hundreds/thousands of buyers and sellers who have placed orders that no one is yet willing to match. ie: if IBM's spot price is at $100, there could still be 10,000 people willing to sell for $101 (called the 'ask' price, for the lowest price someone is currently willing to sell at), and 15,000 willing to buy for $99 (called the 'bid' price, for the highest price someone is currently willing to buy for).  Until someone is willing to buy for $101, then no one will be able to sell at $101. Until someone is willing to sell for $99, no one will be able to buy for $99. Typically orders are placed in the market at a particular limit. Meaning that those orders to buy at $99/sell at $101 are already in the 'system', and will be matched immediately as soon as someone is willing to meet the price on the other side. Now consider general market economics: high demand drives up price, and high supply drives down price. If the details above for IBM were yesterday, and today some news came out that IBM was laying off employees, imagine that another 10,000 people who held shares wanted to sell. Now there would be 20,000 sellers and only 15,000 buyers. If those new sellers were aggressive about wanting to sell, they would have to drop their price to $99, to match the highest buyers in the market. Put together, this means that as more sellers enter the market, supply of shares increases, driving down price. Conversely, as more buyers enter the market, demand for shares increases, driving up share price. As a result of the above, you can say that (all else being equal) if price for a stock goes up, there were more buyers that day, and if price goes down, there were more sellers that day. On the face of it, that is not necessarily true, because you could have the same number of buyers and sellers, one side could have simply decreased/increased their acceptable price to match the other side. "Consider the futures market. Traders buy and sell gold futures, but very few contracts, relatively speaking, result in delivery. The contracts are sold, and ""Open interest"" dwindles to near zero most months as the final date approaches. The seller buys back his short position, the buyer sells off his longs.  When I own a call, and am 'winning,' say the option that cost me $1 is now worth $2, I'd rather sell that option for even $1.95 than to buy 100 shares of a $148 stock. The punchline is that very few option buyers actually hope to own the stock in the end. Just like the futures, open interest falls as expiration approaches." You're assuming options traded on the open market. To close open positions, a seller buys them back on the open market. If there's little on offer, this will drive the price up.