Choosing the correct IRS filing status is a fairly straightforward process, and is based on your marital status as well as your financial contribution to a household. According to the tax laws given by the IRS, the filing status you choose is based on your status on the final day of the calendar year for which you are filing. So, if you are married on December 31, 2009, your IRS filing status for the 2009 tax year would either be "married, filing jointly" or "married, filing separately."
Of course, in many instances it can be more complicated to choose your IRS filing status. A married couple is free to choose to file jointly or separately, though certain deductions, such as interest paid on school loans, may be affected. In addition, certain tax benefits are lost if a married couple chooses to file separately rather than jointly. If you have any questions about which way to file would be the most beneficial, direct them to a tax accountant.
If your spouse passed away during the tax year, you may still file jointly and note that it is a final return for the deceased individual. This is not true if you married again during the same calendar year. Another option may be to file as "qualifying widow(er) with dependent child," though once again, this filing status requires certain parameters to be met.
The other two options for IRS filing status are "single" and "head of household." Single filing status is easy to determine; if you are not married, divorced, or legally separated, you will generally file as single. This is also true if you live alone and have no dependents, though sometimes single individuals with dependent children will still file as "single." The "head of household" is the most complicated IRS filing status to choose, though it also provides significant tax benefits.
In order to qualify as a "head of household," you need to contribute more than half of the living expenses to the home. Generally, you must not be married and will need a qualifying individual to live with you in order to declare yourself head of household. Do your research when you are choosing your IRS filing status, because selecting the incorrect one increases the likelihood of being audited. Each IRS filing status will come with a different standard deduction amount, which is important to consider whether or not you are itemizing your deductions, as well as a number of other laws and restrictions.