My wife submitted a tax return married filed single and now realizes that was an error and we should have filed jointly. I have not yet filed what should we do?

[Zbucklyo]

You will have to amend your wife's tax return by filling out Form 1040X, change your filing status to Married Filing Jointly, and add in your income.  If you expect a balance due, follow Karen's advice, and make a payment.  You might want to extend for yourself - your wife doesn't need to extend since she's filed.

[KarenJ]

You will need to file a federal and state extension by tomorrow and pay any balance due.

https://ttlc.intuit.com/questions/1899507-how-do-i-amend-married-filing-separately-returns-to-marrie...

[paul-bres]

Thank you - one challenge is that her tax return has not yet been accepted. What should I do if it is not accepted before the deadline?

[Zbucklyo]

If it rejects, you don't need to extend, or amend.  Just change the filing status and add in your income.