If you're married, you can't file your taxes using the "single" filing status. However, this doesn’t mean you necessarily have to file a joint return. In addition to the married filing jointly status, you have the option of filing separately, and in some cases, as head of household.
Married Filing Jointly
The only requirements to using the married filing jointly filing status are the existence of a legal marriage between a man and woman and the consent of both taxpayers to file a joint return. When married couples combine their income and expenses, it generally results in a lower tax bill than if they filed separately. The drawback is that in most cases you’re jointly liable for everything reported on the return, regardless of how much of the income reported on it, if any, is earned by you.
Married Filing Separately
Choosing the married filing separately status and preparing your own return can give you peace of mind that you’ll never be responsible for your spouse’s tax debt -- but this comes with a price. Certain tax credits, such as the earned income credit, are not available to married couples who file separately. Overall, you'll usually end up paying more in taxes. And, you must both take the same type of deduction: you must either both take the standard deduction, or you must both itemize.
Head of Household
One of the requirements of filing as head of household is that you be unmarried or considered unmarried on the last day of the tax year. Although the legality of your marriage is governed by state law, the IRS will consider you unmarried if you and your spouse live in separate homes for at least the last six months of the tax year. You must also have a child, stepchild or foster child who resides with you for more than half of the tax year, pay more than half the cost of keeping up the home and be eligible to claim the child’s exemption. The benefit is that you’ll take a larger standard deduction than a single or married filing separately filer.
A principal and significant difference between the three filing statuses is the different taxes that apply to the same income. To illustrate, suppose in 2011 you earn $110,000 of income, your spouse doesn't work and you're only eligible to take the standard deduction and exemptions, including one for your dependent child. Filing a joint return with your wife would result in taxable income of $87,300 and a tax bill of $14,081. If you filed separately, your taxable income increases to $96,800 and will cost you $21,146 in tax. And you if were eligible to file as head of household, you would report taxable income of $94,100 and pay $18,299 of income tax.