Consequences of Filing Married Separately
Couples who are married on the last day of the tax year basically have two filing status options when filing their tax returns: either married filing jointly (MFJ) or married filing separately (MFS) returns. Generally, filing MFJ will produce the better tax result. However, other factors – usually personal or financial rather than tax-related – can come into play that cause taxpayers to choose to file MFS returns.
Whatever the reason for filing MFS, the consequences encountered when filing separate returns are as follows.
Taxpayers are frequently blindsided when their filing status changes because of a life event such as marriage, divorce, separation or the death of a spouse. These occasions can be stressful or ecstatic times, and the last thing most people will be thinking about are the tax ramifications. But the ramifications are real, and the following are some of the major tax complications for each situation. 
A taxpayer’s filing status for the year is based upon his or her marital status at the close of the tax year. Thus, if you get married on the last day of the tax year, you are treated as married for the entire year. The options for married couples are to file jointly or separately. Both statuses can result in surprises – some pleasant and some unpleasant – for individuals who previously filed as unmarried.