Unless your spouse wants to amend the MFS return already filed to a joint return, you also need to file MFS. You cannot file a joint return because your spouse's return using his/her Social Security number has already been filed. Looks like you are stuck with MFS if you want to get something filed quickly for the sake of the stimulus check. If you want to amend it later to a joint return, you have three years to amend it.
If your spouse itemized, you have to itemize, too. If your spouse used standard deduction then you must also use standard deduction.
When you are in My Info it will ask if you were married...say yes....next it will ask if you want to file together with your spouse. Say NO.
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
