For millions of taxpayers who are divorced or separated, the IRS has made life a little easier. But it's making life harder -- and justly so -- for those of you who get alimony income and haven't been paying taxes on it. Five important new rules:

*If you're living apart from your spouse, taking care of the children, but don't yet have a legal separation agreement, you'll find it much easier to file as "head of household," which gives you a lower tax.

Under the new rules, a married person living separately is considered a "head of household" under the following circumstances: your child made his home with you for more than six months; you file a separate tax return; your spouse did not live with you for the last six months of 1985; you pay more than half the cost of keeping up your home; and you can claim the child as a dependent (because he or she lived with you for more than half the year).

Even if you do not claim the child as a dependent, you are still considered a head of household if you formally relinquished the dependency exemption to your spouse by signing the new form 8332.

If you don't meet these tests, you have to report as a "married person filing separately," which increases sharply the amount of tax you will have to pay. In this situation, a smarter approach is to file taxes jointly, if your spouse will agree.

Warning: The IRS's free tax-help publication, "Your Federal Income Tax," gives conflicting and misleading information on this point. So do all the private publications that reprint the IRS's work.

However, the information in the IRS instruction book that comes with your 1040 and 1040A is correct and reasonably clear. So is the H&R Block Income Tax Workbook -- one of the most understandable tax guides in the market.

If you are divorced or legally separated on the last day of the year (as opposed to merely living apart), you can file as head of household if: your child lived with you for more than six months; and you pay more than half the cost of maintaining your home. In this case, the child does not have to be your tax dependent.

If you're divorced or legally separated, and do not meet all the tests in the paragraph above, you will have to file as a single person. That gives you a higher tax rate than if you had qualified as head of household.

*Another important rule change should end many arguments over which parent gets the child's $1,040 dependency exemption. Starting this year, that valuable tax break automatically goes to the parent who has custody of the child for most of the year, usually the mother.

You qualify for the exemption under the following circumstances: the child was in your custody for more than six months; you were divorced or legally separated; and if not yet legally separated, your spouse did not live with you for the last six months of 1985.

The custodial parent can pass the exemption to her ex-spouse, if she wants, by signing Form 8332, which has to be filed with his tax return. She might do so in return for higher child-support payments. But Sidney Kess of KMG Main Hurdman advises that she sign the form only for one year at a time, as one small way of enforcing that those higher payments will, in fact, be made.

Warning: This simple new rule may not apply to the formerly married who signed separation agreements prior to 1985. If your agreement stated that the parent without custody was entitled to take the exemption, he still gets it, as long as he paid at least $600 toward the child's support.

*Many women receiving alimony payments have been evading taxes on that income by not reporting it, and the IRS had no easy way of catching them. But this year, your tax returns can be computer-checked for truth.

The person paying alimony (and claiming his payments as a tax deduction) now has to list the name and Social Security number of the person receiving it, on pain of a $50 fine. A wife who refuses to disclose her Social Security number for this purpose also can be fined $50. (Note that child support is not considered taxable income.)

You usually have to pay estimated taxes on your alimony income. If you didn't, expect a penalty.

*You can now fund an IRA with alimony income, if you can afford it.

*Whichever spouse pays for the child's medical or dental expenses may now use those bills toward his or her medical tax deduction. It no longer matters whether or not you can claim the child as a dependent.