When you file your income taxes, you have to denote your filing status. The Internal Revenue Service recognizes five statuses: single, married filing jointly, married filing separately, head of household and qualifying widow(er) with dependent child.
The IRS uses different tax brackets for different filing statuses. For example, the tax bracket for single filers are generally higher than those of married couples filing jointly who have the same taxable income.
The income tax brackets even out at the top for all filing statuses except married filing separately, which is half the size of the other statuses. For example, for the 2010 tax year, income over $373,650 is taxed at 35 percent if your filing status is single, married filing jointly, qualifying widow(er) with dependent child or head of household.
Certain tax deductions can only be claimed by people of a certain filing status. For example, as of 2010 you cannot claim the tuition and fees deduction if your filing status is married filing separately.