I was working on my 2019 tax return and I discovered an error in filing of my 2018 return. The mistake I made was I filed married filing separately and I itemized deductions on one return and the othe

[BrandiLO]

If you need to make changes to a prior year return that was already filed and accepted, you will need to amend your return. Please click here for instructions. 

[smac1951]

Does it matter whether I use my tax return or my spouses tax return. I want to refile as MFJ instead of the two returns I did as MFS?

[DeanM15]

To file a Married Filing Jointly amended return, it does not matter which one you start with.

I would start with the most complicated return, as all that data will come through. You will need to enter all the data from the other return into TurboTax. 

[smac1951]

OK, I decided to amend my return since it was the more complicated then my Spouse's return. I opened my original tax return from 2018 in turbotax and clicked on the amend section filled out everything. The one thing that TurboTax did not do was to add together the refund/payment for both returns and add it on line 18 or 21. In my case it is an overpayment by the IRS so I need to add it to the line 18. In order to do this I had to open forms in TurboTax click on the 1040X and scroll down to smart box "Original 2018 return overpayment smart worksheet". I then added my federal refund and my spouse's federal payment to get the corrected amount on line 18. I just want to confirm that this is correct way to do this since TurboTax did not have any instructions on how to go about doing this when changing from MFS to MFJ. Any comment this would be appreciated?

[JosephF8]

If you both got refunds for 2018 you would add those amounts together. If you got a refund and your spouse had a payment due you would subtract the amount of the payment due from your refund amount to get net refund.