Here are the basic rules regarding who should file, when to file and where.

Who Must File

Many lower-income individuals are simply not required to file a tax return because their gross income does not equal or exceed a specified filing minimum. The threshold is generally based on the sum of the taxpayer's personal exemption and standard deduction.

For example, in 1990 a single taxpayer under age 65, who cannot be claimed as a dependent on someone else's return, is entitled to a personal exemption of $2,050 and, if not itemizing, a standard deduction of $3,250; accordingly the filing minimum for this taxpayer is $5,300, as shown in Chart A of Section 2 "Filing Requirements" in the booklet.

Chart A lists the 1990 floor for each category of taxpayer. If your gross income equals or exceeds the amount shown for your filing status, you must file a federal tax return. Gross income here refers to the sum of money, goods and property you received and on which you must pay income tax. It excludes nontaxable income.

Filing Requirements For Dependents

In recent years, the filing rules for children and other dependents have become more complicated, but as for other taxpayers, the determination of whether a return is required is based on the sum of one's personal exemption and standard deduction.

Dependents are not allowed to claim a personal exemption for themselves, so their filing threshold virtually always will be lower than their nondependent counterpart. Their filing requirement is therefore determined by the standard deduction to which they are entitled.

Dependents under 65 who are not blind are allowed a standard deduction equal to the greater of $500 or earned income, up to the standard deduction amount allowed to nondependent counterparts.

There are numerous variations to this basic rule, depending on one's age, marital status and visual acuity. The IRS has provided a chart, Chart B in Section 2 of the booklet, summarizing the filing requirements for children and other dependents.

If your dependent child under age 14 -- on Jan. 1, 1991 -- must file, there may be an alternative. In certain circumstances, you may elect to report such child's income on your own return, in which case a return will not have to be filed by your child. Form 8814 is used to make the election and report the income. See also the discussion regarding "Other Income" reportable on line 22, Form 1040.

Other Filing Situations

Even if it appears you do not need to file a return because your gross income doesn't exceed the Chart A or Chart B minimum, according to Chart C you must still file if:

You want a refund of tax withheld from your pay.

You received advance earned income credit payments from your employer, in anticipation of the earned income credit.

You owe Social Security taxes on tips.

You owe the alternative minimum tax.

You owe excise tax on certain retirement plan distributions.

You had net earnings from self-employment of $400 or more.

When to File

Your federal income tax return for 1990 must be postmarked no later than midnight Monday, April 15, 1991. If you can't make it for any reason, you can get an automatic four-month extension, to Aug. 15, 1991, by filing Form 4868 by April 15.

Form 4868 doesn't extend the due date for paying any tax you owe. You must make a "proper" estimate of your total tax liability, or the extension may not be regarded as valid and you could incur failure-to-file penalties. If you owe additional tax, send it with Form 4868. Make your check or money order payable to "Internal Revenue Service" and write your Social Security number on it along with "1990 Form 4868."

If you file the extension on or just before April 15, send it by certified mail, so you will have proof that you filed it on time. And keep a copy of Form 4868. You must attach a copy to your return when you file.

If you live outside the United States or Puerto Rico and your main place of business is also outside the United States or Puerto Rico, you can get an automatic two-month extension, extending both the time to file and the time to pay any tax due. Interest will still be due on the unpaid tax from April 15 until the date paid. When you do file your return, attach an explanation to show that you met the requirements.

Where to File

Residents of the District, Maryland and Virginia should mail their returns -- or their Forms 4868 -- to the Internal Revenue Service Center, Philadelphia, Pa. 19255.

How to File

Although most people fill out and file a collected sheaf of paper forms and schedules, it is now possible to file your return electronically and get your refund quicker.

For instructions about how to assemble your paper forms, schedules and attachments -- including W-2s, address label and payment -- see the discussion in the section called "And Finally" below, after the section on calculating your tax.

For information about filing electronically, see the electronic filing discussion above, in the section called "What's New for 1990."

Which Form?

Any taxpayer may use the long Form 1040. If you qualify under the rules that follow, you may use either the simple Form 1040EZ or Form 1040A, which allows a few more items.

Form 1040EZ

You may be able to use this simplest form for 1990 if:

You are single with no dependents.

You are not 65 or older or blind.

You had less than $50,000 of taxable income.

Your income came only from wages, salaries, tips, taxable scholarships and fellowships, and not more than $400 taxable interest.

You use the standard deduction and don't claim any adjustments to income or tax credits.

You made no estimated tax payments for 1990.

Form 1040A

The criteria for using Form 1040A are the same as for 1040EZ except:

Any taxpayer -- not just taxpayers who are single, under 65, and not blind -- may be eligible to use the form.

You may have income from any amount of interest and dividends; distributions from an IRA, a pension or annuity, or Social Security; and unemployment compensation.

You and your spouse may claim a deduction for IRA contributions.

You may claim the child and dependent care credit, the credit for the elderly or disabled, or the earned income credit.

Estimated tax rules apply. Namely, the form accommodates estimated tax payments, allows for credit of any overpayment to 1991 estimated tax and imposes penalty for underpayment of estimated tax.

Form 1040

If your situation isn't accommodated by one of the other forms -- see the booklet instructions under the heading "You Must Use Form 1040 If:" -- use Form 1040.

Before You Start

Before you start, it's a good idea generally to review your prior year's return, including any summary data and notes you may have from the prior year. This may remind you of long-forgotten items that could help with this year's return.

Information returns such as W-2s and 1099s for certain income and expense items can help you organize much of your tax data.

Unless you have a question about their accuracy, you may be able to rely on them and forgo trying to reconcile them with your records.

Start your tax preparation by focusing on your income items and any so-called adjustments to income -- that is, the items reportable on lines 24 to 29 of Form 1040 -- so that you can get a handle on your adjusted gross income on line 31 of Form 1040 -- your AGI -- a key number in determining your tax. The gross income information will help you figure out whether you must file. The AGI information will help you figure out how much effort you need to expend on certain categories of itemized deductions.

Medical expenses and miscellaneous itemized deductions tend to be the two most difficult categories to analyze and two of the hardest categories to actually deduct. Medical expenses are deductible only to the extent they exceed 7.5 percent of adjusted gross income (AGI). Miscellaneous itemized deductions are deductible only to the extent they exceed 2 percent of AGI.

Calculate these percentages of your estimated AGI before you delve into any analysis of your medical or miscellaneous expenses. Then try to make some reasonable estimate of how much, at most, you may have in the way of medical expenses and miscellaneous itemized deductions. If you aren't close to the 7.5 percent and 2 percent floors, don't spend any more time worrying about your medical or miscellaneous deductions. If you're close, you should still wait until later to spend more time on medical or miscellaneous deductions.