why would closing price of a stock be different from different sources, and which would you take as the real price?
"There is more than one exchange where stock can be traded.   For example, there is the New York Stock Exchange and the London Stock Exchange.  In fact, if you look at all the exchanges, there is essentially continuous trading 24/7 for many financial instruments (eg US government bonds). The closing price quoted in papers is usually the price at the close on the NYSE.  However, options close after that and so there is after-the-close trading in many stocks with active options, so the price at the close of options trading at CBOE is often used. The ""real"" price is always changing.  But for the purpose of discussion, using the closing price in NYSE (for NYSE listed stocks) is pretty standard and unlikely to be questioned.  Likewise, using Bloomberg's price makes sense. Using some after-hours or small market quote could lead to differences with commonly accepted numbers - until tomorrow :)"
Everything would depend on whether the calculation is being done using the company's all-time high intraday trading price or all-time high closing price. Further, I've seen calculations using non-public pricing data, such as bid-offer numbers from market makers, although this wouldn't be kosher. The likelihood is that you're seeing numbers that were calculated using different points in time. For the record, I think Apple has overtaken Microsoft's all-time highest market cap with a figure somewhere north of $700 billion (nominal).  Here's an interesting article link on the subject of highest-ever valuations: comparison of highest market caps ever I'd add, this is actually the way any stock opens every day, i.e. the closing price of the prior day is what it is, but the opening price will reflect whatever news there was prior to the day's open. If you watch the business news, you'll often see that some stock has an order imbalance and has not opened yet, at the normal time. So, as Geo stated, those who were sold shares at the IPO price paid $38, but then the stock could open at whatever price was the point where bid and ask balanced.   I snapped a screen capture of this chart on the first day of trading, the daily charts aren't archived where I can find them. This is from Yahoo Finance. You can see the $42 open from those who simply wanted in but couldn't wait, the willingness of sellers to grab their profit right back to what they paid, and then another wave of buying, but then a sell-off. It closed virtually unchanged from the IPO price. The Wikipedia has an article on money flow index. The article which you link to correctly uses the typical price. You state that you are comparing the closing prices, which is incorrect. I'm making no statement on the validity of the money flow index itself, just answering your question. "Stock prices are set by bidding. In principle, a seller will say, ""I want $80."" If he can't find anyone willing to buy at that price, he'll either decide not to sell after all, or he'll lower his price. Likewise, a buyer will say, ""I'll pay $70."" If he can't find anyone willing to pay that price, he'll either decide not to buy or he'll increase his price. For most stocks there are many buyers and many sellers all the time, so there's a constant interplay. The typical small investor has VERY little control of the price. You say, ""I want to buy 10 shares of XYZ Corporation and my maximum price is $20."" If the current trending price is below $20, your broker will buy it for you. If not, he won't. You normally have some time limit on the order, so if the price falls within your range within that time period, your broker will buy. That is, your choice is basically to buy or not buy, or sell or not sell, at the current price. You have little opportunity to really negotiate a better price. If you have a significant percentage of a company's total stock, different story. In real life, most stocks are being traded constantly, so buyers and sellers both have a pretty good idea of the current price. If the last sale was ten minutes ago for $20, it's unlikely anyone's going to now bid $100. They're going to bid $20.50 or $19.25 or some such. If the last sale was for $20 and your broker really came to the floor and offered to buy for $100, I suppose someone would sell to him very quickly before he realized what an outrageous price this was. I use TD Ameritrade, and on their web site, if I give a price limit on a buy that's more than a small percentage above the last sale, they reject it as an error. I forget the exact number but they won't even accept a bid of $80 if the stock is going for $40. They might accept $41 or $42, something like that." In addition to D. Stanley's very fine answer, the price of stocks change as a result of changing market conditions and the resulting investor estimation of its effect on the company's future earnings. Take these examples. Right now, in the USA, there is a housing shortage; that is, there are fewer houses available for purchase than there are willing buyers. Investors will correctly assume that the future earnings of home builders will be higher than they were, say ten years ago. Seeking to capitalize on these higher earnings, they will try to buy the stocks. However, the current owners of the stock, potentially the sellers, know the same thing as the investor-buyer and therefore demand a premium to entice a sale. The price of the stock has risen. The reverse is true, also. Brick and mortar retailers are declining as more consumers prefer on-line retail shopping. The current owners of these stocks will probably want to sell their stock before it is worth even less. The investor-buyer also knows the same facts; that future earnings will most likely be less for these companies. The potential buyer offers a very low price to entice a sale. The price of the stock has fallen. Finally, the price of stocks rise and fall with general market conditions. As an example, assume that next months jobs report is released showing that 350,000 new jobs were created in July. Investors will believe that if companies are hiring, then the companies are doing well; they are selling products and services at a higher than expected rate, requiring that they add new employees. They will also conclude that those 350,000 new employees will be spending their salaries to buy not just food, clothing and shelter, but also a few luxuries like a newer car, a TV, perhaps even a new home (please see paragraph 2!). All of these companies will have more business, more earnings and, likely, a higher stock price. I still can't understand why there is a price discrepancancy.  There isn't. It's the same stock and price differences between such major exchanges will always be minimal. I think you simply haven't paid attention to the date range. It seems Google finance only has data for FRA:BMW reaching back to 2011, so if you try to look at the development of your investment since 2009, you're not getting comparable data. As stock prices have declined, the net worth of people has come down. Imagine owning a million shares of a stock worth $100/share. This is worth $100,000,000. Now, if the stock is suddenly trading at $50/share then some would say you have lost $50,000,000. The value of the stock is less. The uncertainty is always there as there are differences between one day's close and another day's open possibly. The sale price is likely to be near the last trade is what is being used here. If you place a market order to sell your stock, the price may move between the time the order is placed and when it is filled. There are limit orders that could be used if you want to control the minimum price you get though you give up that the order has to be filled as otherwise people could try to sell shares for millions of dollars that wouldn't work out well. Prices are adjusted for return and not payout.  So if you take the ratio of the close price and the adjusted close price, it should remain constant. The idea behind a total return (back-)adjustment is to give you a feeling how much money you would have needed back then to reach the price today under the premise that all distributions (dividends, spin-offs, etc.) are reinvested instantly and that reinvestment doesn't cost anything. "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." 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. "Probably the best way to investigate this is to look at an example. First, as the commenters above have already said, the log-return from one period is log(price at time t/price at time t-1) which is approximately equal to the percentage change in the price from time t-1 to time t, provided that this percentage change is not big compared to the size of the price. (Note that you have to use the natural log, ie. log to the base e -- ln button on a calculator -- here.) The main use of the log-return is that is a proxy for the percentage change in the price, which turns out to be mathematically convenient, for various reasons which have mostly already been mentioned in the comments. But you already know this; your actual question is about the average log-return over a period of time. What does this indicate about the stock? The answer is: if the stock price is not changing very much, then the average log-return is about equal to the average percentage change in the price, and is very easy and quick to calculate. But if the stock price is very volatile, then the average log-return can be wildly different to the average percentage change in the price. Here is an example: the closing prices for Pitchfork Oil from last week's trading are: 10, 5, 12, 5, 10, 2, 15. The percentage changes are: -0.5, 1.4, -0.58, 1, -0.8, 6.5 (where -0.5 means -50%, etc.) The average percentage change is 1.17, or 117%. On the other hand, the log-returns for the same period are -0.69, 0.88, -0.88, 0.69, -1.6, 2, and the average log-return is about 0.068. If we used this as a proxy for the average percentage change in the price over the whole seven days, we would get 6.8% instead of 117%, which is wildly wrong. The reason why it is wrong is because the price fluctuated so much. On the other hand, the closing prices for United Marshmallow over the same period are 10, 11, 12, 11, 12, 13, 15. The average percentage change from day to day is 0.073, and the average log-return is 0.068, so in this case the log-return is very close to the percentage change. And it has the advantage of being computable from just the first and last prices, because the properties of logarithms imply that it simplifies to (log(15)-log(10))/6. Notice that this is exactly the same as for Pitchfork Oil. So one reason why you might be interested in the average log-return is that it gives a very quick way to estimate the average return, if the stock price is not changing very much. Another, more subtle reason, is that it actually behaves better than the percentage return. When the price of Pitchfork jumps from 5 to 12 and then crashes back to 5 again, the percentage changes are +140% and -58%, for an average of +82%. That sounds good, but if you had bought it at 5, and then sold it at 5, you would actually have made 0% on your money. The log-returns for the same period do not have this disturbing property, because they do add up to 0%.  What's the real difference in this example? Well, if you had bought $1 worth of Pitchfork on Tuesday, when it was 5, and sold it on Wednesday, when it was 12, you would have made a profit of $1.40. If you had then bought another $1 on Wednesday and sold it on Thursday, you would have made a loss of $0.58. Overall, your profit would have been $0.82. This is what the average percentage return is calculating. On the other hand, if you had been a long-term investor who had bought on Tuesday and hung on until Thursday, then quoting an ""average return"" of 82% is highly misleading, because it in no way corresponds to the return of 0% which you actually got!  The moral is that it may be better to look at the log-returns if you are a buy-and-hold type of investor, because log-returns cancel out when prices fluctuate, whereas percentage changes in price do not. But the flip-side of this is that your average log-return over a period of time does not give you much information about what the prices have been doing, since it is just (log(final price) - log(initial price))/number of periods. Since it is so easy to calculate from the initial and final prices themselves, you commonly won't see it in the financial pages, as far as I know.  Finally, to answer your question: ""Does knowing this single piece of information indicate something about the stock?"", I would say: not really. From the point of view of this one indicator, Pitchfork Oil and United Marshmallow look like identical investments, when they are clearly not. Knowing the average log-return is exactly the same as knowing the ratio between the final and initial prices." If you download the historical data from Yahoo, you will see two different close prices. The one labeled 'Close' is simply the price that was quoted on that particular day. The one labeled 'Adj Close' is the close price that has been adjusted for any splits and dividends that have occurred after that date.  For example, if a stock splits 10:1 on a particular date, then the adjusted close for all dates prior to that split will have been divided by 10. If a dividend is paid, then all dates prior will have that amount subtracted from their adjusted quote. Using the adjusted close allows you to compare any two dates and see the true relative return. He said he's using MSCI World as a benchmark. MSCI World is not an exchange. The point is the same security listed in different places has different prices, so how do you describe the equity beta of the company to MSCI World if you have multiple and different return streams? This is a real problem to consider and you just dismiss it entirely. Stock prices reflect future expectations of large groups of people, and may not be directly linked to traditional valuations for a number of reasons (not definitive). For example, a service like Twitter is so popular that even though it has no significant revenue and loses money, people are simply betting that it is deeply embedded enough that it will eventually find some way to make money. You can also see a number of cases of IPOs of various types of companies that do not even have a revenue model at all. Also, if there is rapid sales growth in A but B sales are flat, no one is likely to expect future profit growth in B such that the valuation will remain steady. If sales in A are accelerating, there may be anticipation that future profits will be high. Sometimes there are also other reasons, such as if A owns valuable proprietary assets, that will hold the values up. However, more information about these companies' financials is really needed in order to understand why this would be the case. Anyone who wants to can use any method they want. Ultimately, the price of the stock will settle on the valuation that people tend to agree on. If you think the priced in numbers are too low, buy the stock as that would mean that its price will go up as the future earnings materialize. If you think it's too high, short the stock, as its price will go down as future earnings fail to materialize. The current price represents the price at which just as much pressure pushes the price up as down. That means people agree it's reasonably approximating the expected future value. Imagine if I needed money now and sold at auction whatever salary I make in 2019. How much will I make in 2019? I might be disabled. I might be a high earner. Who knows? But if I auction off those earnings, whatever price it sells for represents everyone's best estimate of that value. But each participant in the auction can estimate that value however they want. If you want to know what something is worth, you see what you can sell it for.