Why does a stock's price fluctuate so often, even when fresh news isn't available?
News about a company is not the only thing that affects its stock's price. There is also supply and demand.  That, of course, is influenced by news, but it is not the only actor.  An insider, with a large position in their company's stock, may want to diversify his overall portfolio and thus need to sell a large amount of stock.  That may be significant enough to increase supply and likely reduce the stock's price somewhat. That brings me to another influence on stock price: perception.  Executives, and other insiders with large positions in their company's stock, have to be careful about how and when they sell some of that stock as to not worry the markets.  Many investors watch insider selling to gauge the health of the company. Which brings me to another important point.  There are many things that may be considered news which is material to a certain company and its stock.  It is not just quarterly filings, earnings reports and such.  There is also news related to competitors, news about the economy or a certain sector, news about some weather event that affects a major supplier, news about a major earthquake that will impact the economy of a nation which can then have knock-on effects to other economies, etc... There are also a lot of investors with varying needs which will influence supply and demand.  An institutional investor, needing to diversify, may reduce their position in a stock and thus increase supply enough that it impacts the stock's price.  Meanwhile, individual investors will make their transactions at varying times during the day.  In the aggregate, that may have significant impacts on supply and demand. The overall point being that there are a lot of inputs and a lot of actors in a complicated system.  Even if you focus just on news, there are many things that fall into that category. News does not come out at regular intervals and it does not necessarily spread evenly.  That alone could make for a highly variable environment. "In addition to what @George Marian said, a very large portion of trades are from computer programs trained to make trades when certain apparent patterns are observed.  Since these programs are not all designed in the same way, much of the supply and demand is a result of different algorithms with different ""opinions"" on what the stock is doing." It's the buying and selling of the stock that causes the fluctuation in prices, not the news. People buy and sell all the time, and not just for newsworthy reasons.  They may have to send a child to college, or fix a roof, etc.  Or they may be technical traders looking for signals.  All kinds of reasons. "Investors are ""forever"" comparing the prices of stocks to other stocks. As others have pointed out, this is done faster and more frequently nowadays with high-speed computer programs. There may be no ""fresh"" news on stock A, but if there is fresh news on stock B (as there usually is), the news on B affects the COMPARISON with stock A. That could be what causes trading in stock A that has ""no news.""" according to me it's the news about a particular stock which makes people to buy or sell it mostly thus creates a fluctuation in price . It also dependents on the major stock holder.
Large volume just means a lot of market participants believe they know where the stock price will be (after some amount of time).  The fact that the price is not moving just means that about 50% of those really confident traders think the stock will be moving up, and about 50% of those really confident traders think the stock will be moving down. 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. "This is a classic correlation does not imply causation situation.  There are (at least) three issues at play in this question: If you are swing- or day-trading then the first and second issues can definitely affect your trading.  A higher-price, higher-volume stock will have smaller (percentage) volatility fluctuations within a very small period of time. However, in general, and especially when holding any position for any period of time during which unknowns can become known (such as Netflix's customer-loss announcement) it is a mistake to feel ""safe"" based on price alone. When considering longer-term investments (even weeks or months), and if you were to compare penny stocks with blue chip stocks, you still might find more ""stability"" in the higher value stocks.  This is a correlation alone — in other words, a stable, reliable stock probably has a (relatively) high price but a high price does not mean it's reliable. As Joe said, the stock of any company that is exposed to significant risks can drop (or rise) by large amounts suddenly, and it is common for blue-chip stocks to move significantly in a period of months as changes in the market or the company itself manifest themselves. The last thing to remember when you are looking at raw dollar amounts is to remember to look at shares outstanding.  Netflix has a price of $79 to Ford's $12; yet Ford has a larger market cap because there are nearly 4 billion shares compared to Netflix's 52m." If the period is consistent for company X, but occurs in a different month as Company Y, it might be linked to the release of their annual report, or the payment of their annual dividend. Companies don't have to end their fiscal year near the end of the Calendar year, therefore these end of year events could occur in any month. The annual report could cause investors to react to the hard numbers of the report compared to what wall street experts have been predicting. The payment of an annual dividend will also cause a direct drop in the price of the stock when the payment is made. There will also be some movement in prices as the payment date approaches. Stock prices are indeed proportional to supply and demand. The greater the demand for a stock, the greater the price. If they are, would this mean that stock prices completely depend on HOW the public FEELS/THINKS about the stock instead of what it is actually worth? This is a question people have argued for decades. Literature in behavioral finance suggests that investors are not rational and thus markets are subject to wild fluctuation based on investor sentiment. The efficient market theory (EMT) argues that the stock market is efficient and that a stock's price is an accurate reflection of its underlying or intrinsic value. This philosophy took birth with Harry Markovitz's efficient frontier, and Eugene Fama is generally seen as the champion of EMT in the 1960's and onward.  Most investors today would agree that the markets are not perfectly efficient, and that a stock's price does not always reflect its value. The renowned professor Benjamin Graham once wrote: In the short run, the market is a voting machine but in the long run it is a weighing machine. This suggests that prices in the short term are mainly influenced by how people feel about the stock, while in the long run the price reflects what it's actually worth. For example, people are really big fans of tech stocks right now, which suggests why LinkedIn (stock: LNKD) has such a high share price despite its modest earnings (relative to valuation). People feel really good about it, and the price might sustain if LinkedIn becomes more and more profitable, but it's also possible that their results won't be absolutely stellar, so the stock price will fall until it reflects the company's fundamentals. "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." Yes, but only in a relatively short term. False news or speculations can definitely change the stock price, sometimes even significantly. However, the stock price will eventually (in the long-term) correct itself and head to the right direction. I think it's because there are a lot of retail investors in this stock.  They are the ones that tend to overreact on news cycles, so creating bad press or over-hyping bad press really makes the stock price swing. "The fallacy in your question is in this statement: ""The formulas must exist, because prices can be followed real time."" What you see are snapshots of the current status of the stock, what was the last price a stock was traded at, what is the volume, is the price going up or down.  People who buy and hold their stock look at the status every few days or even every few months. Day traders look at the status every second of the trading day.  The math/formula comes in when people try to predict where the stock is going based on the squiggles in the line. These squiggles move based on how other people react to the squiggles.  The big movements occur when big pieces of news make large movements in the price. Company X announces the release of the key product will be delayed by a year; the founder is stepping down; the government just doubled the order for a new weapon system; the insiders are selling all the shares they can. There are no formulas to determine the correct price, only formulas that try to predict where the price may go." 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. 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. "Most likely because they don't know what they're talking about. They all have a belief without evidence that information set X is internalised into the price but information set Y is not. If there is some stock characteristic, call it y, that belongs to set Y, then that moves the gauge towards a ""buy"" recommendation. However, the issue is that no evidence has been used to determine the constituents of X and Y, or even whether Y exists in any non-trivial sense." "The ""random walk"" that you describe reflects the nature of the information flow about the value of a stock.  If the flow is just little bits of relatively unimportant information (including information about the broader market and the investor pool), you will get small and seemingly random moves, which may look like a meander.  If an important bit of information comes out, like a merger, you will see a large and immediate move, which may not look as random. However, the idea that small moves are a meander of search and discovery and large moves are immediate agreements is incorrect.  Both small moves and large moves are instantaneous agreements about the value of a stock in the form of a demand/supply equilibrium.  As a rule, neither is predictable from the point of view of a single investor, but they are not actually random.  They look different from each other only because of the size of the movement, not because of an underlying difference in how the consensus price is reached." "At any moment, the price is where the supply (seller) and demand (buyer) intersect. This occurs fast enough you don't see it as anything other than bid/ask. What moves it? News of a new drug, device, sandwich, etc. Earning release, whether above or below expectations, or even dead-on, will often impact the price.  Every night, the talking heads try to explain the day's price moves. When they can't, they often report ""profit taking"" for a market drop, or other similar nonsense. Some moves are simple random change." "Firstly, if a stock costs $50 this second, the bid/ask would have to be 49/50.  If the bid/ask were 49/51, the stock would cost $51 this second.  What you're likely referring to is the last trade, not the cost.  The last trading price is history and doesn't apply to future transactions. To make it simple, let's define a simple order book.  Say there is a bid to buy 100 at $49, 200 at $48, 500 at $47.  If you place a market order to sell 100 shares, it should all get filled at $49.  If you had placed a market order to sell 200 shares instead, half should get filled at $49 and half at $48.  This is, of course, assuming no one else places an order before you get yours submitted.  If someone beats you to the 100 share lot, then your order could get filled at lower than what you thought you'd get.  If your internet connection is slow or there is a lot of latency in the data from the exchange, then things like this could happen.  Also, there are many ECNs in addition to the exchanges which may have different order books.  There are also trades which, for some reason, get delayed and show up later in the ""time and sales"" window. But to answer the question of why someone would want to sell low... the only reason I could think is they desire to drive the price down."