I filed for an automatic extension in April. I did this jointly with my wife. Can I now file separate returns or must we file jointly?

My guess is yes, if neither of you either together or individually owes money. Why? If there is a tax advantage to changing how you file, you might be courting trouble. On the other hand, if you could amend your return at a future time, incurring the same tax advantage, then you would not be courting trouble. In summary, it seems that you can do as you please, and if you determine officially that you cannot, you may be able to amend the return and do it anyway. I hope that this makes sense with a rereading.

When you applied for the extension, were both your names included? If not, you've left your wife out in the cold. If yes, both of you have until the end of the extension to get your forms mailed in.

If both of you expect refunds, you're not likely to be fined or penalized no matter what happens. If you're still in doubt, just call the IRS back and clarify your filing status with the extension.

(By the way, did you know that filing married-seperate is the worst possible way to file your income tax? It's even worse than filing single!)