How about this for a reasonable method: Calculated State Income tax both with and without Investment Income and use the difference as the amount of State Income tax allocatable to Investment Income. The trouble is getting that number into TT without overridding the entry for Form 8960 line 9b. I get an Smart Check Error that say I will not be able to File Electronically. I would think that TT could run the above method algorithmically allowing the error check to work. Also the 'Form 8960 Wks' wasn't any help with this.
