Not only can using the right filing status affect how much you owe, but it can also affect which credits you are eligible to receive. In fact, the filing status you choose can even determine whether you have to file a tax return at all.
For IRS purposes, anyone who is married on or before December 31st, is considered married for the entire tax year. Special rules apply to same-sex married couples.
If multiple filing statuses apply, you should choose the one with the lowest tax obligation.