If I received a 1099B for noncovered stocks that has $0 for cost basis but I calculated the cost basis in a statement, do I put it in the block or do I adjust the gains?

[mattb587]

I'm wanting to verify if I need to put the calculated cost basis from the monthly statement in the "Total cost or other basis (sum of all Box 1e)" or if I should put $0 as provided in the 1099B form and instead check the "I need to adjust my total cost basis" and adjust the gain by providing a negative number?  Obviously option B, "(cost basis incorrect on form)" would then be checked as well.

[PattiF]

You would adjust the cost basis for the noncovered stocks and enter the cost basis that you have calculated.

[mattb587]

Thank you! Should I plan to submit the monthly statement that I used for calculating the cost basis or just have it handy in case it's needed later? 

[ToddL99]

You do not need to submit proof of your cost basis with your return (or separately). Just keep the cost records on file with your other 2020 tax documents.