For tax purposes, December 31 means more than New Year’s Eve celebrations. It affects your taxpayer filing status . . . the filing status box that will be checked on your tax return for the year. When you file your return, you do so with one of five filing statuses, which depend in part on whether you’re married or unmarried on December 31. More than one filing status may apply, and you can use the one that saves the most tax. It’s also possible that your status options could change during the year. Here are the filing statuses and who can claim them: Single. This status is generally used if you’re unmarried, divorced or legally separated under a divorce or separate maintenance decree governed by state law. ...