@catfoodv The above answer was an old one that migrated over when the user forum changed from Answer Xchange to Real Money Talk. And---you are right---after the filing deadline you cannot switch from married filing jointly to married filing separately, but you CAN amend from separate returns to a joint return.
Since you added to such an old thread, we cannot tell what your own circumstance is. But if one of you filed as HOH or MFS and the other has not yet filed, wait for the return that was already filed to be fully processed before you try to amend and switch to a joint return.
When you are ready--amend the MFS return to make it it a joint return. That ONE return will the the return for the two of you. When you file a joint return it is only ONE return for both spouses together.
https://ttlc.intuit.com/questions/1899507-how-do-i-amend-a-separate-return-to-married-filing-jointly
**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.**
