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In general, your filing status depends on whether you are considered unmarried or married.You are considered unmarried for the whole year if, on the last day of your tax year, you are either:--Unmarried, or--Legally separated from your spouse under a divorce or separate maintenance decree.
For federal tax purposes, the marriage of a same sex couple is treated the same as the marriage of a man to a woman.
However, individuals who have entered into a registered domestic partnership, civil union, or other similar relationship that isn't a marriage under state law aren't married for federal tax purposes.If individuals of the same sex are married, they generally must use the married filing jointly or married filing separately filing status.
Please see some additional details here
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