DavidD66
Expert Alumni

Investors & landlords

If you are confident that the cost basis is correct, you would not need to adjust it.  That would be unusual for ESPP shares, but it is possible.  I would verify that the cost basis is correct on at least one of the transactions reported on the 1099-B.  If the cost basis is incorrect, it most likely is understated which would result in your gain being overstated or loss understated and your paying more tax than required.  

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