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 (usually three years) to show this change in marital status.
If you got married during 2015 your filing status may have changed. You and your spouse will need to decide if you are going to file a joint return or separate returns. There are several tax consequences you should be aware of when making this decision. Generally it is most advantageous to file a joint return. The standard deduction for joint filers is $12,600 and for separate filers it is $6,300 ($0 if your spouse itemized deductions on their separate return). If one spouse itemizes their deductions then the other spouse must also itemize their deductions when they file separate returns. Additionally there are several tax benefits you cannot take if you elect married filing separately:
If you made payments to or for your spouse or former spouse under a divorce or separation instrument, you may be able to take the payments as a deduction if all of the following apply: