generally married filing jointly will produce the lowest tax even when there's a disparity in income. the tax is figured like each of you earned 1/2 the combined taxable income. for example, if married filing separately, all income was ordinary, and you had $25k in taxable income and she had $75K the combined federal taxes would be about $14,900. filling jointly the taxes would be about $13,200 (twice the tax on $50K each if single). then with MFS there are certain tax credits that will be lost, such as the credit for child and dependent care expenses, the earned income credit, the adoption credit, education credits and the deduction for student loan interest. Also, if one itemizes both must itemize, or if one uses the standard deduction both must use it. However, there can be circumstances where MFS can be beneficial. here's a link to a Turbotax thread on when MFS can save taxes
https://turbotax.intuit.com/tax-tips/marriage/when-married-filing-separately-will-save-you-taxes/L7F...
