Congratulations -- you're now down to the bottom line. Add all the items you have entered in the payments section and enter the total on line 61. Now compare that number with the total tax you calculated on line 53. Is the total of your payments larger than your tax liability? Smile! Enter the difference on line 62, then sit back and wait for your refund check.

Well, there is still one small decision for you to make. If you want the entire overpayment refunded to you, enter on line 63 the same amount you have on line 62. But if you normally pay estimated tax and want all or part of the overpayment applied to your 1988 tax, enter the amount you want the IRS to hold on line 64, and any balance you want refunded by check on line 63. (The total of lines 63 and 64 should equal line 62.)

The bad news: If the total tax is larger than total payments, the difference is the amount you owe Uncle Sam. Attach a check or money order, payable to Internal Revenue Service, for the amount due. Write your Social Security number on the check (so it can be identified if it is detached) and attach it to the tax return.

If the balance due the IRS is $500 or more and the underpayment is more than 20 percent of your total tax liability, you may have to complete Form 2210 to determine if an interest penalty is due. (Farmers and fishermen should use Form 2210F.)

A penalty may be due because insufficient tax was withheld from your pay or because you had income from self-employment, investments, pensions or other source on which tax was not withheld and you either failed to file an estimated tax return or filed but underpaid.

You don't have to complete Form 2210 if you were a U.S. citizen or resident for all of 1986 and had no 1986 tax liability (based on a full 12-month tax year), or if either your total tax liability for 1987 or the tax shortfall is less than $500.

For this year only: A plethora of problems surfaced in 1987 in connection with the new W-4 forms that were intended to permit folks to adjust their tax withholding to meet the requirements of the 1986 tax law. Recognizing this, the IRS announced in late December a blanket waiver, for the 1987 tax year only, of penalties for underpayment caused by underwithholding of tax from wages.

This waiver applies to income from wages or salary only. If you had 1987 income from other sources -- like pension or retirement pay, self-employment, interest and dividends or other investments -- the blanket waiver does not apply to that part of your income.

If you had income from wages and salary and income from other sources and were underwitheld, there is no need to file Form 2210. The IRS will calculate -- and bill you for -- the penalty on any net underpayment based on the ratio of wage income to adjusted gross income, assuming you don't qualify for exemption under the other rules, such as those mentioned below.

If you wish, you may file a 2210 even with wage income as a part of your total income and make the calculations yourself; you certainly should if you can qualify for one of the other waivers. If you had no income from wages or salary and end up with a substantial shortfall, you should, of course, file Form 2210 to calculate any penalty due.

There are other circumstances that will avoid the penalty.

For example, if you had a windfall in December 1987 and filed an estimated tax return to cover it on Jan. 15, 1988, Form 2210 permits you to show income and payments by quarters so you can avoid penalty for failure to pay estimated tax for the first three quarters.

Instructions for various situations are printed on the reverse side of Form 2210; additional information is found in Publication 505. The IRS may waive the penalty if the underpayment is due to a casualty, disaster or other unusual circumstance that would make the penalty unfair. The penalty may also be waived for a taxpayer who retired, at age 62 or older, or became disabled in either 1986 or 1987.

If you are required to complete Form 2210, attach the form to your tax return and check the box under line 65 of Form 1040. (You may not use either short form.) If Form 2210 shows that you owe a penalty, write the amount in the space indicated, and include it in the payment you send IRS.

In the event of a shortfall on which a penalty is due, you may be tempted to wait to see if the IRS catches it. However, an underpayment is usually picked up on the initial review of a return -- and if the IRS bills you, it will charge interest in addition to the penalty.

If you end up owing additional tax to the IRS, it is perfectly legal to wait until April 15 to mail the return and the payment. Unless the amount is small, it makes sense to hold on to your dollars, earning interest as long as possible.

But if you're due a refund, send the return as soon as it's completed. Not only will you get your claim registered sooner, but the waiting time between filing and refund is also shorter during the early part of the filing season, before the IRS is swamped with returns.

Despite what you may have heard, filing early doesn't increase the odds of being audited. But don't let the prospect of a large refund con you into carelessness. Review your work carefully. If possible, have someone else go over the return, particularly the arithmetic.

Make sure you have attached all W-2 forms, and a payment -- with your Social Security number on it -- if one is required.

When you are assembling your return, check the "Attachment Sequence No." on each form and schedule, directly under the year "1987." That number indicates the order in which the forms and schedules are to be placed behind the basic tax form. Any supporting documents or explanatory notes go at the back of the package after the last official form.

After you have assembled the entire package in proper order and checked the attachments, you're ready to sign and date the return. (Remember that both spouses must sign on a joint return.)

Put the entire return in the addressed envelope that came in the instruction booklet, add enough stamps, drop it in a mailbox -- then sit back with a sigh of relief, knowing that this necessary chore is out of the way for another year.