How to re-coup losses from providing incorrect 1099B in 1e data for years.

[richmo3]

I've been selling my employee stock for years. I just noticed that the cost basis on 1099B in 1e is different (always lower) compared to the supplemental information Fidelity provides. I've been filling for years without providing the updated amount in the "Corrected cost basis" field so it seems like I've been paying more taxes than I should have for years.
Is there a way of re-couping these losses?

[DawnC0 · Accepted solution]

You can file amended tax returns to recoup some of the taxes you overpaid.  Underreporting your cost basis will definitely create a situation of over taxation.  See below for instructions for amending your returns in TurboTax.  Please note, you can only go back three years from the due date of the return when filing amended returns for additional refunds.  So, you have until April 15, 2020, to file an amendment for your 2016 tax return.  

How to Amend

[richmo3]

Thanks for the insightful answer!