(MONEY Magazine) – The worksheet at right will help you compare your 1990 and 1991 federal tax bills. Most of the lines are self-explanatory. For the others, follow these directions: --Line 5: If your adjusted gross income exceeds $100,000, the amount you enter for 1991 can't top 80% of the itemized deductions you expect to claim on your return, not including write-offs for medical expenses, investment interest and theft and casualty losses.

--Line 6: If your taxable income exceeds the amounts cited, you will have to complete 6a, the small worksheet at upper right to figure out the correct amounts to enter. --Lines 9 to 11 show employees how to compute the Medicare tax. If you also have self-employment income, get an accountant's help to fine-tune the figures for you. --Lines 12 to 16 help you compare the impact of federal taxes on your purchases of gas, cigarettes, alcoholic beverages, airline tickets and luxury items for 1990 and 1991.

CHART: NOT AVAILABLE CREDIT: Charts by Serban Epure Source: Moss Adams, Seattle CAPTION: 6a. EXEMPTION PHASEOUT FOR HIGH EARNERS 8a. TAX FOR MARRIED JOINT FILERS 8b. TAX FOR SINGLE FILERS