"What you left out of the quote was the assumption that the couple has but one job between them. In such a case a joint return is going to result in less tax than would separate returns. With most of the income being reported on one separate return, the effective rate would be higher. In a community property state, community income, including wages, is split between the separate returns regardless of who earned it. Thus, with some income on the nonworking spouse's return, there might be an advantage with respect to medical bills, etc."Please see my second post. It seems to me that, in a community property state, there is no gain fom filing MFS to exploit separate personal expenses unless they are paid from separate funds (which are not easy to establish for the common folk). And therefore the outcome is determined by the (MFJ vs MFS) tax bracket situation, and that is a non-linear, dis-continuous equation. The post seems to reflect a situation wherein the income and deuctions would be split 50/50 in a community propert state (resultinr in a higher tax). In other states the spouse would have a large, unusable sch A deduction.I sugest that this may be one of the most diffficult to analyze (no less explain) options available to the taxpayer. And (short of a rather lenghty tutorial), the proper answer is: If in doubt go MFJ otherwise, see pub 555 and an above average professional.