Your federal income tax filing status depends on whether you're married or unmarried. Married couples can file joint returns, usually the best option, while unmarried individuals typically file individual returns. A head of household status is sort of in between; it's for single people who may have been married but are now considered unmarried and have dependents who rely on them for support.
The test for your filing status is the last day of the tax year. If you're married as of Dec. 31, you're considered married for the entire year. Even common-law marriages count if you live in a state that allows them. If you're unmarried or considered unmarried on the last day of the year, you can 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.
The standard deduction for married couples filing joint returns is $11,600 as of 2012 or $13,900 if you and a spouse are both over 65. That applies to your joint taxable income. For head of household, it is $8,500, applied to your single income. That's $3,300 more than you would get if you filed as single or as married filing separately.
You can be a head of household even if you're married but your spouse didn't live with you at any time during the last six months of the year, unless the absence was temporary due to special situations like illness or military service. Your dependent can be a child or any relative or person who meets the IRS qualifications; a parent doesn't have to live with you for you to be a head of household. You also can file jointly if you're married but live apart and are not legally separated.
If you file a joint return, you combine your incomes and deductions, even if they are not equal. You can provide most of the income, for instance, and still claim the joint standard deduction. Or if you and a spouse both have incomes, you can combine itemized deductions for mortgage interest, charitable donations or educational and medical expenses.
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