Medical Expenses

• The IRS only allows you to deduct medical expenses that exceed 7.5 percent of your adjusted gross income. If you file jointly, both spouses' incomes and both spouses' expenses get rolled into one, which may limit the amount of the deduction. However, if you file separately, more of the deduction may be permitted for one spouse. For example, if one spouse has an adjusted gross income of $40,000 and $10,000 in medical expenses, that spouse could claim a $7,000 deduction. However, if she files jointly and her husband adds $60,000 of income and no medical expenses, the deduction drops to just $2,500.
  
  

Miscellaneous Deductions

• Your total miscellaneous deductions must add up to more than 2 percent of your adjusted gross income before you can claim any adjustments. Miscellaneous deductions include unreimbursed job expenses like mileage driven between jobs or for business duties, malpractice premiums and union dues, tax preparation fees and other expenses including depreciation on home computers used for investments and losses on IRAs. If one spouse has most of the miscellaneous deductions, filing separately could ensure a larger portion of the deductions will be allowable because the 2 percent floor will be lower.
  
  

Casualty and Theft Losses

• If you suffer a loss from theft or disaster and your insurance does not reimburse you, you can claim a deduction on your income tax return as long as you filed a timely claim. However, the IRS requires you to reduce the amount of your deduction by 10 percent of your adjusted gross income. Given this high hurdle, the only way to qualify for some couples may be to file separate returns so that the person who claims the loss has a low enough adjusted gross income to allow a deduction.
  
  

Questionable Spouse

• If your spouse has been audited by the IRS in the past, or if you question the deductions that your spouse claims, filing separately protects you against future IRS audits. When you file a joint return, both spouses are liable for the information submitted and, even if your spouse was the one who lied on the return, your assets are fair game for the IRS to take unless you qualify for the innocent spouse exemption, which requires you to prove that you were unaware of the deceptive return.