The adjusted close number is not something I figure out but use the number found at Yahoo finance.
I sold stock I inherited and know that the basis is the value of the stock on the date of death, but don’t know if I use the actual closing price or the adjusted closing price. Trying to factor in the reinvested dividends and stock splits seem like a lot of work so using the adjusted close looked like an easy way to take into account these factors. Thanks.

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Close price adjusted for dividends and splits, adjusted closing stock dividends and splits