Depending on your financial circumstances, your total federal tax liability may include any of several other types of taxes in addition to the basic income tax. After you have entered the various tax credits to which you may be entitled, it's time to move on to this next section of Form 1040. Self-Employment Tax

If you were self-employed and had net earnings of more than $400 in 1985, you must complete and attach Schedule SE to determine if you owe any Social Security tax on those earnings.

If you earned $39,600 or more in salary or wages subject to Social Security withholding, then you already have reached the ceiling on contributions for 1985 and will not be liable for Social Security tax on additional earnings from self-employment. But you still must attach a completed Schedule SE to your return to show the numbers.

If you do owe Social Security tax on some earnings from self-employment, the rate is 11.8 percent. The imposed rate for 1985 is in fact 14.1 percent, including 11.4 percent for old age, survivors and disability insurance plus 2.7 percent for hospital insurance. But there is a credit of 2.3 percent allowed on 1985 returns, resulting in the 11.8 percent effective rate.

Do not send payment of self-employment tax to the Social Security Administration. Any tax computed on Schedule SE goes on line 51 of Form 1040, where it gets added to your tax liability. The IRS is responsible for transferring both the amount of the payment and the information from Schedule SE to the SSA. Alternative Minimum Tax

If you're a high-bracket taxpayer with considerable income sheltered from tax, you may be liable for a "minimum" tax. The alternative minimum tax was established to prevent taxpayers from sheltering so much of their ordinary income with sophisticated -- though legal -- tax avoidance techniques that they paid little or no tax on large amounts of income.

The alternative minimum tax is imposed on selected forms of income known as "tax preference items," including such things as incentive stock options, certain types of accelerated depreciation and depletion, otherwise excluded interest and dividends, the untaxed (60 percent) portion of long-term capital gains (except on sale of a personal residence) and selected Schedule A deductions.

A minimum tax of 20 percent is imposed on the excess of "alternative minimum taxable income" over normal taxable income, after subtracting some deductions and an exemption based on your filing status. The exemption for single taxpayers is $30,000; on joint returns $40,000, and $20,000 for married taxpayers filing separately (as well as for estates and trusts).

Any liability for alternative minimum tax is determined by completing Form 6251. Any tax due is carried to line 52 of Form 1040. You must attach Form 6251 to your 1040 if you had tax preference income in 1985 (other than the dividend exclusion or the 60 percent capital gain deduction) even if no tax liability results. Get a copy of IRS Publication 909 for additional information. ITC Recapture

If you took an investment tax credit in a previous year, but disposed of the property on which the credit was taken before the expiration of its normal life, you may have to repay a portion of the credit taken earlier. Use Form 4255 for the calculations, and enter any required recapture amount on line 53 of Form 1040. Tip Income

Use Form 4137 and line 54 to compute any Social Security tax liability for tips received but not reported to your employer or on tips you had reported but on which your employer had not withheld the tax. IRA Withdrawal

Withdrawal of funds from an IRA before reaching age 59 1/2 (except in the event of death or disability) requires payment of a 10 percent penalty in addition to the normal tax due. This additional tax is reported on Form 5329, then carried to line 55 of Form 1040. Advance EIC Payments

If you received advance payments from your employer against an anticipated earned income credit, you do not offset those advance payments against what you now calculate you are due.

Instead, you enter the total of those advance payments (as shown on the W-2 from your employer) in the "Other Taxes" section. There is no designated line on the tax forms for entering advance EIC payments. On Form 1040, write "AEIC" and the amount received on the dotted line on line 56, then include that amount (together with any amounts from lines 50 through 55) in the "total tax" in the right-hand column of that line. If you're using Form 1040A, follow a similar procedure, using line 23.

Then further on, when you get to the earned income credit itself (line 59 of Form 1040, line 24b of the 1040A), enter the full amount of the credit to which you are entitled.