In the event of a corporate spin-off, how can I calculate the correct cost basis for each company's shares?
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.
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### Instruction:
In the event of a corporate spin-off, how can I calculate the correct cost basis for each company's shares?

### Response:
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.