If you're married, you have the option to file a joint return with your spouse as long as you were legally married at the end of the year. No matter how you filed the previous year, you always have the option to file jointly or separately each successive year. Even if you filed jointly the previous year, you can file separately this year if there is a compelling reason to do so.
Check Both Methods
If you're married, run your income tax numbers as if you were filing separately and as if you were filing jointly to determine which one gives you the bigger refund or lower payment. There's nothing stopping you from switching back and forth from year to year. As a general rule, it makes more financial sense to file jointly because you will get more deductions and credits that way. However, if one spouse piles up high medical expenses in a given year it might be better to file separately.
Mark Kennan is a writer based in the Kansas City area, specializing in personal finance and business topics. He has been writing since 2009 and has been published by "Quicken," "TurboTax," and "The Motley Fool."