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How does Yahoo finance adjust stock data for splits and dividends?
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.