Loss Carry Over

No, you did not report the transactions that resulted in the losses so you cannot use the loss from his tax return to offset your gains.  Also just in case you aren't aware, when your dad passed away, you received a step-up in basis for all the stocks in the joint account.  A cost basis step-up adjusts the cost basis of an inherited asset to its fair market value on the date the owner died.  As the surviving joint tenant, your new cost basis consists of the following:  the FMV of your father's interest in the account holdings, plus your original cost basis in the property. If your father purchased all the assets in the account, then his interest in the original cost basis is 100% and your cost basis is now the Fair Market Value of the stock on the date of your father's death.