Retirement tax questions

Thank you.  I was not clear in my question and I'll give some more detail now.

I am trying to find how the tax free interest number is calculated.  This is important to me as in the State of MA I pay taxes on those bonds which are not MA bonds.  

Tax exempt interest is reported on 1040 line 2a.   This number comes from

    1040/1040 SR Wks line 2a.  This number comes from

     Schedule B  Interest Income Smart Worksheet  However The sum of the tax exempt interest in Box 8 does not equal the value on the 1040 line 2a.  Subtracting Accrued Interest got the number a lot closer but not the same as reported.  The Bond Premium paid was MUCH more than the difference between the values.

How can I track back to see how the tax free interest was actually calculated by Turbo Tax to make sure I am not paying tax on the bond premium?