I have a similar situation.  Dependent can be claimed on mother's return for 6 mos of the year.  Dependent got his own job just prior to high school graduation.  There is an HSA deduction on the dependents W-2 for himself only, not family.  On the 8889-T form I check self only and tried only checking for the last 6 mos of the year for the HSA coverage but get the error message that a dependent cannot claim an HSA deduction.  In this case can the dependent be claimed on the mother's return when he earned $37,000 versus his mother who earned $42,000 before expenses (self employed).