From the IRS: Seven Facts to Help you Choose the Right Filing Status.
The filing status you choose when you file your 2012 tax return will affect the tax breaks you’ll qualify for, your standard deduction amount, and ultimately the amount of tax you’ll pay. Are you single, head of household, married filing jointly, or married filing separately?
Here are seven facts that will help you choose the right status.
1. Your marital status as of the last day of the year is your marital status for the entire year.
2. If you qualify for more than one status, choose the one that results in the lowest tax liability for you.
3. Single filing status is likely to be your filing choice if you are not married or you are divorced or legally separated.
4. Married individuals can file a joint return. If your spouse died during 2012, you generally may still file a joint return for 2012.
5. Married couples may file “married, filing separately” if they choose.
6. “Head of household” status is available to you if you are not married and you paid more than half the cost of maintaining a home for yourself and a child.
7. The status “qualifying widow(er) with dependent child” is available if your spouse died during 2010 or 2011 and you have a dependent child. Other conditions may apply.