Filing a separate tax return while married is like packing a parachute -- most of the time you don't need it, but when you do, it really pays off.

The overwhelming majority of married couples do, and should, file jointly. Usually, couples can save thousands of dollars filing together.

When married people file separately, the IRS takes a host of incentives off the table, including credits for child and dependent care, as well as deductions for adoption expenses, education loan interest and IRA contributions.

But there are several special circumstances when it may pay to file separately. And in remarriage situations, where you and your spouse lived a life, complete with tax returns, before you ever met, the equation becomes even more complicated.

When you file jointly, the IRS considers you and your spouse as one entity. If your new spouse owes money to the IRS because of a joint return from a previous marriage, the IRS can seize your new joint refund to pay the debt.

Before you file, ask yourself these questions:

1. Have either of you had a lot of medical expenses in the past year? Expenses are calculated against your total income, so the smaller the income, the more of the expenses you get to deduct. If your spouse's income is not included, then you will get to take more of your medical expenses as a deduction. But remember, by filing separately you will lose other deductions, so run the numbers and see what works best. And in many cases, especially if the return is complicated, get a professional to help.

2. Do you or your spouse claim investment expenses or non-reimbursed business expenses? Do you or your spouse live off investments and, consequently, have a lot of investment expenses? While it won't cover losses, investment expenses can include anything from financial and legal advice to brokerage fees. What about non-reimbursed business expenses, things like travel, meals or office supplies? These are calculated using the same method as medical bills, the smaller the income, the more of the actual expense you are allowed to deduct. Limit the income by filing separately, and you may save money.

3. Does your spouse owe child support? The IRS will seize tax refunds to pay outstanding child support. If you sign a joint return with a spouse who owes money, you are risking your portion of the refund as well.

4. Does your spouse owe money to the IRS? If your spouse owes money and you want your refund, it may pay to file separately.

5. Has your spouse ever been audited? Is your spouse in the middle of an audit? If your spouse is still doing whatever it was that attracted the ire of the IRS, claiming a hobby as a business, playing fast and loose with deductions, etc., file separately.

6. Is your spouse self-employed? "People who are self-employed tend to be very aggressive when it comes to claiming deductions," says Stuart Sorkin, a CPA and tax attorney with Stuart H. Sorkin PC, a law firm based in Bethesda, Md. In a joint return, both parties are liable. If you have money, assets or an attachable salary, guess who the Feds will come after?

7. Do you thoroughly understand your spouse's business, sources of income and tax return? Do your spouse's financial dealings pass the "gut check" test? Are you being asked to sign returns you don't understand? When you ask questions, does your spouse get evasive or angry?

Many times, women find themselves in this situation. But Jan Warner, co-author of "Flying Solo," a nationally syndicated divorce column, remembers a husband who became suspicious after his wife got involved in a family enterprise. She was vague and refused to explain her business dealings. From that point, the husband insisted on filing separate returns. Now divorced, the man has a healthy business while his ex-wife is in the middle of a major -- and expensive -- battle with the IRS.

"He's off the hook," says Warner. "He didn't file a return with her."

Dana Dratch is a freelance writer based in Atlanta.