If you are separated from your spouse during tax season what do you file as

Your tax filing status is controlled by your marital status as of the last day of the year. If you are married on Dec. 31, you must file as married, unless you would qualify under the special Head of Household rules. It would probably be in your mutual interest to file a joint return,. even though you are separated, normally that turns out to be true. People uisually pay substantially less tax when they file as married filing jointly than married filing separately. If they file separately, they lose out on several levels. If you file a joint return, an added benefit is that there is no issue of who claims the exemptions.

From the IRS web site:

"Considered married. You are considered married for the whole year if on the last day of your tax year you and your spouse meet any one of the following tests.
You are married and living together as husband and wife.

You are living together in a common law marriage that is recognized in the state where you now live or in the state where the common law marriage began.

You are married and living apart, but not legally separated under a decree of divorce or separate maintenance.

You are separated under an interlocutory (not final) decree of divorce. For purposes of filing a joint return, you are not considered divorced."