The five filing categories of prior years weren't changed by the 1986 tax law: single, married filing a joint return, married filing separately, head of a household, and qualifying widow(er).

The category you use is determined by your marital status, household living arrangements and the people dependent on you for support.

Your filing status determines which column you go to in the tax tables or which tax rate schedule you use, as well as the amount of the standard deduction you get to claim (if you don't itemize). It may also affect your claim for such things as the child care credit and the earned income credit.

For tax purposes, your marital status was established by your circumstances on Dec. 31, 1987. If you were married on that date, you are considered to have been married for the entire year. But if you were unmarried then -- whether never married, divorced, legally separated or widowed in a prior year -- you are considered single for all of 1987. (However, if your spouse died in 1987 and you hadn't remarried by the end of the year, you may qualify to file a joint return anyway.)

Single, Head of a Household

If you were not married on Dec. 31, 1987, generally you must file your return as a single person (category 1). However, you may qualify as head of a household (category 4) and end up paying less tax if you meet any one of these tests:

You paid more than half the expense of maintaining your home, and it was also the principal home for more than half the year of your unmarried child, stepchild, adopted child or grandchild, whether or not the child qualified as your dependent.

You paid more than half the cost of maintaining your home and it was also the principal home for more than half the year of any other relative you claim as a dependent (but not a dependent under a multiple support agreement).

You paid more than half the cost of maintaining a home that was the principal home of your dependent mother or father, even if you didn't live there yourself. Support of a parent in a nursing or rest home is equivalent to the maintenance of a home. To satisfy the six-month residence requirement, a person is considered to have lived in your home during temporary absences for vacation, school or hospitalization.

Married?

Most married persons file a joint return (category 2). You may elect to file separate returns (category 3), but in most circumstances a joint return provides the lower total tax.

Unless you and your spouse lived apart for the entire year, you must file a joint return to claim the tax credit for the elderly on Schedule R.

Further, if you are receiving Social Security benefits and decide to file separately even though you're married, the income floor for determining taxability of those benefits is zero, so that half your Social Security payments would be taxable without regard to the amount of your other income.

If you elect to file separate returns, you both must use the same method for computing tax liability. That is, if one itemizes deductions, the other must also itemize and may not use the standard deduction.

If you and your spouse were living apart but were not legally separated, you may elect to file a joint return. This may result in a lower combined tax than filing separately -- but each of you is then individually responsible for payment of the entire tax.

You may file as single (category 1) if you were married but lived apart for at least the last six months of the year and you paid more than half the cost of maintaining a home that was also the principal home of your dependent child. Filing as single generally will result in a lower tax than using category 4, married filing separately.

Recently Widowed?

If your husband or wife died during 1987 and you had not remarried by Dec. 31, you may file a joint return for 1987 only, on which you claim the personal exemption of your deceased spouse as well as your own. Sign the return yourself, then write "surviving spouse" under your signature. Enter the date of your spouse's death in the name and address block at the top of the form.

If you were not the executor or administrator of the estate, the personal representative (if one has been appointed) also must sign the return. The personal representative may have filed, or may intend to file, a separate "final" income tax return for the deceased. And an estate tax return, if required, may have an impact on the income tax return. You may need professional help in this situation.

If your husband or wife died in 1985 or 1986 and you haven't remarried by the end of 1987, you may be eligible to file as a qualifying widow(er) (category 5) if you meet both of these tests: You were eligible to file a joint return in the year of your spouse's death (whether or not you actually filed that way).

Your home was the principal residence during 1987 of a child whom you may claim as a dependent.

When you file as a qualifying widow(er), you are given the right to use the joint return rates; however, this is not a joint return, and you may not claim a personal exemption for your deceased spouse.