Almost all married taxpayers will get the best results if they file their tax return jointly. There are very few situations in which filing separately makes sense, and it almost always costs the taxpayers more money to do so. The two most common situations in which it makes sense to file separately:
You and your spouse are in the process of divorcing, and are legally separated. If you don't trust one another, it may make sense to file separately, limiting your tax liability to only the items for which each of you are legally responsible. If you can't seem to cooperate long enough to prepare and file a joint tax return, it probably also makes sense to file separately. If one party is completely non-compliant when it comes to filing tax returns, the other spouse is better off filing a separate return in order to meet her or his obligations regardless of what the other spouse does.
It may make sense to file separately if both spouses are itemizing deductions and one has high medical expenses compared to her or his income. Medical deductions are only deductible if they exceed 7.5% of income, and a spouse with low income and high medical expense may therefore benefit from filing separately.
Couples who are married and file separately almost always pay more tax than if they would have filed jointly, so keep that in mind when deciding whether to file jointly or separately.
Tracy L. Coenen, CPA, MBA, CFE performs fraud examinations and financial investigations for her company Sequence Inc. Forensic Accounting, and is the author of Essentials of Corporate Fraud.