Based on IRS instructions and the information you enter in TaxAct, the TaxAct® program determines what amount (if any) needs to appear on Lines 4a and 4b of Form 1040U.S. Individual Income Tax Return. Usually, if the amount is fully taxable, Line 4a is left blank and the total distribution is entered on Line 4b. Exceptions to this are listed in the IRS Instructions for Form 1040 and 1040-SR.