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.
"There is no fundamental, good reason, I think; ""that's just how it's done"" (which is what all the other answers seem to be saying, w/o coming out and admitting it). Just guessing, but I'll bet most of the reason is historical: Before up-to-the-moment quotes were readily available, that was a bit tedious to calculate/update the fund's value, so enacted-laws let it be done just once per day.  (@NL7 quotes the security act of 1940, which certainly has been updated, but also still might contain the results of crufty rationales, like this.) There are genuinely different issues between funds and stocks, though: One share of a fund is fundamentally different from one share of stock: There is a finite supply of Company-X-stock, and people are trading that piece of ownership around, and barter to find an mutually-agreeable-price.  But when you buy into a mutual-fund, the mutual-fund ""suddenly has more shares"" -- it takes your money and uses it to buy shares of the underlying stocks (in a ratio equal to its current holdings).  As a consequence: the mutual fund's price isn't determined by two people bartering and agreeing on a price (like stock); there is exactly one sane way to price a mutual fund, and that's the weighted total of its underlying stock.  If you wanted to sell your ownership-of-Mutual-Fund-Z to a friend at 2:34pm, there wouldn't be any bartering, you'd just calculate the value based on the stated-value of the underlying stock at that exact moment. So: there's no inherent reason you can't instantaneously price a mutual fund.  BUT people don't really buy/sell funds to each other -- they go to the fund-manager and essentially make a deposit-or-withdraw.  The fund-manager is only required by law to do it once a day (and perhaps even forbidden from doing it more often?), so that's all they do. [Disclaimer: I know very little about markets and finance. But I recognize answers that are 'just because'.]" "So you're basically saying that average market fluctuations have an affect on individual stocks, because individual stocks are often priced in relation to the growth of the market as a whole?  Also, what kinds of investments would be considered ""risk free"" in this nomenclature?" "You seem to be assuming that ETFs must all work like the more traditional closed-end funds, where the market price per share tends—based on supply and demand—to significantly deviate from the underlying net asset value per share. The assumption is simplistic. What are traditionally referred to as closed-end funds (CEFs), where unit creation and redemption are very tightly controlled, have been around for a long time, and yes, they do often trade at a premium or discount to NAV because the quantity is inflexible. Yet, what is generally meant when the label ""ETF"" is used (despite CEFs also being both ""exchange-traded"" and ""funds"") are those securities which are not just exchange-traded, and funds, but also typically have two specific characteristics: (a) that they are based on some published index, and (b) that a mechanism exists for shares to be created or redeemed by large market participants. These characteristics facilitate efficient pricing through arbitrage. Essentially, when large market participants notice the price of an ETF diverging from the value of the shares held by the fund, new units of the ETF can get created or redeemed in bulk. The divergence quickly narrows as these participants buy or sell ETF units to capture the difference. So, the persistent premium (sometimes dear) or discount (sometimes deep) one can easily witness in the CEF universe tend not to occur with the typical ETF. Much of the time, prices for ETFs will tend to be very close to their net asset value. However, it isn't always the case, so proceed with some caution anyway. Both CEF and ETF providers generally publish information about their funds online. You will want to find out what is the underlying Net Asset Value (NAV) per share, and then you can determine if the market price trades at a premium or a discount to NAV. Assuming little difference in an ETF's price vs. its NAV, the more interesting question to ask about an ETF then becomes whether the NAV itself is a bargain, or not. That means you'll need to be more concerned with what stocks are in the index the fund tracks, and whether those stocks are a bargain, or not, at their current prices. i.e. The ETF is a basket, so look at each thing in the basket. Of course, most people buy ETFs because they don't want to do this kind of analysis and are happy with market average returns. Even so, sector-based ETFs are often used by traders to buy (or sell) entire sectors that may be undervalued (or overvalued)." "When people (even people in the media) say: ""The stock market is up because of X"" or ""The stock market is down because of Y"", they are often engaging in what Nicolas Taleb calls the narrative falacy. They see the market has moved in one direction or another, they open their newspaper, pick a headline that provides a plausible reason for the market to move, and say: ""Oh, that is why the stock market is down"". Very rarely do statements like this actually come from research, asking people why they bought or sold that day. Sometimes they may be right, but it is usually just story telling. In terms of old fashioned logic this is called the ""post hoc, ergo proper hoc"" fallacy. Now all the points people have raised about the US deficit may be valid, and there are plenty of reasons for worrying about the future of the world economy, but they were all known before the S&P report, which didn't really provide the markets with much new information. Note also that the actual bond market didn't move much after hearing the same report, in fact the price of 10 year US Treasury bonds actually rose a tiny bit. Take these simple statements about what makes the market go up or down on any given day with several fistfuls of salt." When stocks have a change in price it is because of a TRADE. To have a trade you have to have both a buyer and a seller.  When the price of a security is going up there are an equal amount of shares being sold as being bought. When the price of a security is going down there are an equal amount of shares being bought as being sold.  There almost always is an unequal amount of shares waiting to be sold compared to the amount waiting to be bought. But waiting shares do not move the price, only when the purchase price and the sale price agree, and a trade occurs, does the price move.  So the price does not go down because more shares are being sold. Neither does the price go up because more shares are being bought. There are many things that can make a company's share price go up or down. Generally, over the long term, the more consistently profitable a company is the more its share price will go up. However, there are times when a company may not be making any profits yet but its share price still goes up. This can be due to forecasts that the company will start making profits in the near future. Sometimes a company may report increased profits from the previous year but makes less than what the market was expecting it to make. This can cause its share price to fall, as the market is disappointed in the results. In the shorter term greed, fear and speculation can make a company's share price move irrationally. When you think the share price should be going up it suddenly falls, and Vis-versa. When interest rates are low, companies with higher dividend yields (compared to bank account interest rates) become high in demand and their shares generally go up in price. As the share price goes up the dividend yield will be reduced unless the company continues to increase the dividend it distributes to shareholders. When interest rates start to rise these companies become less favourable as they are seen as higher risk comparable to similar returns from having one's money in the safety of the bank. This can cause the share prices to fall. These are just some of the reasons that make a company's share price move up or down. As humans are an irrational bunch often ruled by emotions, sometimes the reasons share prices move in a particular direction can be quite confusing, but that is the nature of the financial markets. It always bumps right before the 1/4 report.  For some reason, after 80 quarters, people buy amazon stock just incase they under promised and over delivered.  That's happened like 1 or 2 times.  They are so consistent, that I assume the make heavy fiscal investments in the week leading up to quarter close just so they don't A few reasons.  First, it's hard to buy a stock that has never gone up, and isn't necessarily wise to do so.  Even if you just wait for a stock go down, what if you wait and it goes up two dollars, then drops 10 cents?  Has it gone up or down?  When should you buy it? In general, your idea is correct, the higher the price the less you should want the stock.  But in some sense, the past price is irrelevant, you can't buy it at the past price.  You should buy it now if it's the best option now.  And that is based on your assessment of whether it's future prospects are worth the current price (and in fact enough worth enough to make buying the stock the best economic decision you can currently make). Finally, the price may have gone up for a reason.  The company may have done something, or some information about the company may have become known, that affects it's future prospects.  That might make it a better deal, perhaps even better than it was before the price increase.