From www.irs.gov:  IRS TAX TIP
Using the correct filing status is very important when you file your tax return. You need to use the right status because it affects how much you pay in taxes. It may even affect whether you must file a tax return.
When choosing a filing status, keep in mind that your marital status on Dec. 31 is your status for the whole year. If more than one filing status applies to you, choose the one that will result in the lowest tax.
Note for same-sex married couples. New …