Filing Status 
Head of Household
Single or separated taxpayers should check to see if they qualify for head of household filing status. This filing status allows a taxpayer to take a higher standard deduction, possibly be eligible for a lower tax bracket, and perhaps qualify for the earned income credit.

Annulled Marriages
If you obtain an annulment that declares your marriage never existed, you are considered unmarried for this and any previous tax years. You must amend your tax returns for all the tax years not affected by the statute of limitations for filing a return to show this change in marital status.
End of Year
Your filing status depends on whether you are married or unmarried on December 31 of a tax year. If you live apart from your spouse and meet certain tests you may be considered unmarried for the entire year. If you are divorced under a final decree by the last day of the year (state law prevails), you are considered unmarried for the entire year.

Married Filing Joint or Married Filing Separate
If you're married, you have a choice of filing status: married filing joint or married filing separate. To be sure that you pay the lowest tax, figure your return both ways. It's usually advantageous for a married couple to file jointly. However, if the husband's and wife's income is about the same, they may pay more in taxes by filing joint depending on the rest of the return.