How does Yahoo finance adjust stock data for splits and dividends?
For stock splits, let's say stock XYZ closed at 100 on February 5.  Then on February 6, it undergoes a 2-for-1 split and closes the day at 51.  In Yahoo's historical prices for XYZ, you will see that it closed at 51 on Feb 6, but all of the closing prices for the previous days will be divided by 2.  So for Feb 5, it will say the closing price was 50 instead of 100. For dividends, let's say stock ABC closed at 200 on December 18.  Then on December 19, the stock increases in price by $2 but it pays out a $1 dividend.  In Yahoo's historical prices for XYZ, you will see that it closed at 200 on Dec 18 and 201 on Dec 19.  Yahoo adjusts the closing price for Dec 19 to factor in the dividend. Should be noted that pacoverflow's answer is wrong. Yahoo back-adjusts all the previous (not current or future) values based on a cumulative adjustment factor. So if there's a dividend ex-date on December 19, Yahoo adjusts all the PREVIOUS (December 18 and prior) prices with a factor which is: 1 - dividend / Dec18Close "Yahoo's ""Adj Close"" data is adjusted for splits, but not for dividends. Despite Yahoo's webpage's footnote saying  *Close price adjusted for dividends and splits. we can see empirically that the ""Adj Close"" is only adjusted for splits. For example, consider Siemens from Jan 27, 2017 to Mar 15, 2017: The Adj Close adjusts for splits: On any particular day, the ""Adj Close"" is equal to the ""Close"" price divided by the cumulative product of all splits that occurred after that day. If there have been no splits after that day, then the ""Adj Close"" equals the ""Close"" price. Since there is a 2-for-1 split on Mar 14, 2017, the Adj Close is half the Close price for all dates from Jan 27, 2017 to Mar 13, 2017. Note that if Siemens were to split again at some time in the future, the Adj Close prices will be readjusted for this future split. For example, if Siemens were to split 3-for-1 tomorrow, then all the Adj Close prices seen above will be divided by 3. The Adj Close is thus showing the price that a share would have traded on that day if the shares had already been split in accordance with all splits up to today. The Adj Close does not adjust for dividends: Notice that Siemens distributed a $1.87 dividend on Feb 02, 2017 and ~$3.74 dividend on Jan 30, 2017. If the Adj Close value were adjusted for these dividends then we should expect the Adj Close should no longer be exactly half of the Close amount. But we can see that there is no such adjustment -- the Adj Close remains (up to rounding) exactly half the Close amount: Note that in theory, the market reacts to the distribution of dividends by reducing the trading price of shares post-dividend. This in turn is reflected in the raw closing price. So in that sense the Adj Close is also automatically adjusted for dividends. But there is no formula for this. The effect is already baked in through the market's closing prices."
"I don't have anything definitive, but in general positions in a company are not affected materially by what is called a corporate action. ""Corp Actions"" can really be anything that affects the details of a stock. Common examples are a ticker change, or exchange change, IPO (ie a new ticker), doing a split, or merging with another ticker. All of these events do not change the total value of people's positions. If a stock splits, you might have more shares, but they are worth less per share. A merger is quite similar to a split. The old company's stock is converted two the new companies stock at some ratio (ie 10 shares become 1 share) and then converted 1-to-1 to the new symbol. Shorting a stock that splits is no different. You shorted 10 shares, but after the split those are now 100 shares, when you exit the position you have to deliver back 100 ""new"" shares, though dollar-for-dollar they are the same total value. I don't see why a merger would affect your short position. The only difference is you are now shorting a different company, so when you exit the position you'll have to deliver shares of the new company back to the brokerage where you ""borrowed"" the shares you shorted." Many brokerages offer automatic dividend reinvestment. It is very infrequent that these dividends are exactly a whole share. So, if you have signed up for automatic dividend reinvestment, many brokerages will reinvest your dividends and assign to you a fractional share. I can't speak for how these shares work with regards to voting, but I can say that the value of these fractional holdings does change with stock price as if one genuinely could hold a fraction of a share. "Yahoo Finance is definitely a good one, and its ultimately the source of the data that a lot of other places use (like the iOS Stocks app), because of their famous API. Another good dividend website is Dividata.com.  It's a fairly simple website, free to use, which provides tons of dividend-specific info, including the highest-yield stocks, the upcoming ex-div dates, and the highest-rated stocks based on their 3-metric rating system.  It's a great place to find new stocks to investigate, although you obviously don't want to stop there.  It also shows dividend payment histories and ""years paying,"" so you can quickly get an idea of which stocks are long-established and which may just be flashes in the pan. For example:  Lastly, I've got a couple of iOS apps that really help me with dividend investing: Compounder is a single-stock compound interest calculator, which automatically looks up a stock's info and calculates a simulated return for a given number of years, and Dividender allows you to input your entire portfolio and then calculates its growth over time as a whole.     The former is great for researching potential stocks, running scenarios, and deciding how much to invest, while the latter is great for tracking your portfolio and making plans regarding your investments overall." The dividend quoted on a site like the one you linked to on Yahoo shows what 1 investor owning 1 share received from the company. It is not adjusted at all for taxes. (Actually some dividend quotes are adjusted but not for taxes... see below.)  It is not adjusted because most dividends are taxed as ordinary income. This means different rates for different people, and so for simplicity's sake the quotes just show what an investor would be paid.  You're responsible for calculating and paying your own taxes.  From the IRS website: Ordinary Dividends Ordinary (taxable) dividends are the most common type of distribution from a corporation or a mutual fund. They are paid out of earnings and profits and are ordinary income to you. This means they are not capital gains. You can assume that any dividend you receive on common or preferred stock is an ordinary dividend unless the paying corporation or mutual fund tells you otherwise. Ordinary dividends will be shown in box 1a of the Form 1099-DIV you receive. Now my disclaimer... what you see on a normal stock quote for dividend in Yahoo or Google Finance is adjusted. (Like here for GE.) Many corporations actually pay out quarterly dividends. So the number shown for a dividend will be the most recent quarterly dividend [times] 4 quarters. To find out what you would receive as an actual payment, you would need to divide GE's current $0.76 dividend by 4 quarters... $0.19. So you would receive that amount for each share of stock you owned in GE. I also searched for some time before discovering Market Archive, which AFAIK is the most affordable option that basically gives you a massive multi-GB dump of data.  I needed sufficient data to build a model and didn't want to work through an API or have to hand-pick the securities to train from.  After trying to do this on my own by scraping Yahoo and using the various known tools, I decided my time was better spent not dealing with rate-limiting issues and parsing quirks and whatnot, so I just subscribed to Market Archive (they update the data daily). "My answer is Microsoft Excel.  Google ""VBA for dummies"" (seriously) and find out if your brokerage offers an 'API'.  With a brief understanding of coding you can get a spreadsheet that is live connected to your brokers data stream.  Say you have a spreadsheet with the 1990 value of each in the first two columns (cells a1 and b1).  Maybe this formula could be the third column, it'll tell you how much to buy or sell to rebalance them.   then to iterate the rebalance, set both a2 and b2 to =C1 and drag the formula through row 25, one row for each year.  It'll probably be a little more work than that, but you get the idea." Yup. What I wanted to know was where they are pulling it up from. Have casually used Google finance for personal investments, but they suck at corp actions. Not sure if they provide free APIs, but that would probably suck too! :D According to Active Equity Management by Zhou and Jain: When a stock pays dividend, the adjusted price in Yahoo makes the following adjustment: Let T be the ex-dividend date (the first date that the buyers of a stock will not receive the dividend) and T-1 be the last trading day before T. All prices before T are adjusted by a multiplier (C_{T-1} - d_T)/C_{T-1}, where C_{T-1} is the close price at T-1 and d_T is the dividend per share. This, of course means that the price before T decreases. This is just a shot in the dark but it could be intermarket data. If the stock is interlisted and traded on another market exchange that day then the Yahoo Finance data feed might have picked up the data from another market. You'd have to ask Yahoo to explain and they'd have to check their data. You'd have to buy that information. Quoting from this page, Commercial Historical Data Higher resolution and more complete datasets are generally not available for free. Below is a list of vendors which have passed our quality screening (in total, we screened over a dozen vendors). To qualify, the vendor must aggregate data from all US national/regional exchanges as only complete datasets are suitable for research use. The last point is especially important as there are many vendors who just get data from a couple sources and is missing important information such as dark pool trades. They offer some alternatives for free data: Daily Resolution Data 1) Yahoo! Finance– Daily resolution data, with split/dividend adjustments can be downloaded from here. The download procedure can be automated using this tool. Note, Yahoo quite frequently has errors in its database and does not contain data for delisted symbols. 2) QuantQuote Free Data– QuantQuote offers free daily resolution data for the S&P500 at this web page under the Free Data tab. The data accounts for symbol changes, splits, and dividends, and is largely free of the errors found in the Yahoo data. Note, only 500 symbols are available unlike Yahoo which provides all listed symbols. And they list recommendations about who to buy the data from. I've never seen a dividend, split or other corporate action during the day, but I have seen trade suspended a few times when something big happened. The market opening price is not in general the same as the close of the previous day. It can gap up or down and does frequently. I don't know of an api to find out if the dividend was cash or stock, but stock dividends are a lot less common. "I keep spreadsheets that verify each $ distribution versus the rate times number of shares owned. For mutual funds, I would use Yahoo's historical data, but sometimes shows up late (a few days, a week?) and it isn't always quite accurate enough. A while back I discovered that MSN had excellent data when using their market price chart with dividends ""turned on,"" HOWEVER very recently they have revamped their site and the trusty URLs I have previously used no longer work AND after considerable browsing, I can no longer find this level of detail anywhere on their site !=( Happily, the note above led me to the Google business site, and it looks like I am ""back in business""... THANKS!" "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." "Google's RSI is using a 10 period on 2 minute bars - i.e. it is based upon the last 20 minutes of data. Yahoo's RSI is using a 14 period lookback on an undetermined timeframe (you could maybe mouse-over and see what incremental part of the chart is giving) and given the ""choppier"" price chart, probably 30 second or 1 minute bars.   Given the difference in both the period specified and the periodicity of the charts - you should expect different results." "Remember that in most news outlets journalists do not get to pick the titles of their articles.  That's up to the editor.  So even though the article was primarily about ETFs, the reporter made the mistake of including some tangential references to mutual funds.  The editor then saw that the article talked about ETFs and mutual funds and -- knowing even less about the subject matter than the reporter, but recognizing that more readers' eyeballs would be attracted to a headline about mutual funds than to a headline about ETFs -- went with the ""shocking"" headline about the former. In any case, as you already pointed out, ETFs need to know their value throughout the day, as do the investors in that ETF.  Even momentary outages of price sources can be disastrous. Although mutual funds do not generally make transactions throughout the day, and fund investors are not typically interested in the fund's NAV more than once per day, the fund managers don't just sit around all day doing nothing and then press a couple buttons before the market closes.  They do watch their NAV very closely during the day and think very carefully about which buttons to press at the end of the day.  If their source of stock price data goes offline, then they're impacted almost as severely as -- if less visibly than -- an ETF. Asking Yahoo for prices seems straightforward, but (1) you get what you pay for, and (2) these fund companies are built on massive automated infrastructures that expect to receive their data from a certain source in a certain way at a certain time.  (And they pay a lot of money in order to be able to expect that.)  It would be quite difficult to just feed in manual data, although in the end I suspect some of these companies did just that.  Either they fell back to a secondary data supplier, or they manually constructed datasets for their programs to consume."