The Filing Status Test
Your marital status on the last day of the year determines your tax filing status for the entire year. For example, if you get married on December 31st, you are considered to be married for the entire year (even though you were only married for one day out of the year), and you can select “married filing jointly” as your filing status on that year’s tax return. Even common-law marriages count if you live in a state that allows them.
On the other hand, if you get divorced on the last day of the year, you are considered to be single for the entire year. However, you may qualify as head of household if you have a child or other dependent who lived with you and you paid more than half the cost of supporting the household.