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system
in the event of a corporate spin-off, how can i calculate the correct cost basis for each company's shares?
user
having all of the numbers you posted is a start. it's what you need to perform the calculation.  the final word, however, comes from the company itself, who are required to issue a determination on how the spin-off is valued. say a company is split into two. instead of some number of shares of each new company, imagine for this example it's one for one. i.e. one share of company a becomes a share each in company b and company c. this tell us nothing about relative valuation, right? was b worth 1/2 of the original company a, or some other fraction? say it is exactly a 50/50 split. company a releases a statement that b and c each should have 1/2 the cost basis of your original a shares. now, b and c may very well trade ahead of the stock splitting, as 'when issued' shares. at no point in time will b and c necessarily trade at exactly the same price, and the day that b and c are officially trading, with no more a shares, they may have already diverged in price. that is, there's nothing you can pull from the trading data to identify that the basis should have been assigned as 50% to each new share. this is my very long-winded was of explaining that the company must issue a notice through your broker, and on their investor section of their web site, to spell out the way you should assign your basis to each new stock.
assistant