Especially if you had some holdings that were transferred to Fidelity from another broker.....the proper cost basis may not have been transferred too. Depends on how long you held them before you transferred to Fidelity and then sold the security....at one point, the IRS started to require cost basis to be transferred to the new Broker, but before a certain year, the basis never was..
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*
