I believe there is a calculation error for South Carolina in the desktop version.
If you itemize deductions, South Carolina requires adding back in the federal deduction for state income taxes (effectively, you can't deduct your SC income tax from your SC income).
SC1040 has a specific line for this, line 1(a).
There are a few other lines for specific addbacks (out of state losses on rental property, etc) and then there is a line E which is a catchall for other miscellaneous additions (for example, the QBI deduction).
TurboTax is putting the SC state income tax addback into line 1(a) - as it should - but then also putting this state income tax addback into line 1(e) along with the QBI and any other misc addbacks. Effectively, TT Desktop adds the income tax back in two places, thereby overestimating your SC taxable income and so your SC tax due.
Within the program front end, it appears to handle the calculation correctly:
Going into the detail screen, you see the tax addback and the QBI
But when it comes time to generate the SC1040, it puts the entire amount (tax + QBI) in line 1(e) and duplicates the tax addback on line 1(a) where it actually belongs. Incidentally, the $1976 value appears to be the correct value, as this is also reflected on worksheet A where the exact addback value is calculated. The $1978 in the detail above appears to be a minor error. However, it cannot be edited in the screen above.
Anyway, if I'm correct and this is a bug within TurboTax, it needs to be corrected. I'm going to redo my state return from scratch and see if maybe it was user error or if there's a way to trick it so it doesn't double-count the tax addback.
Thanks,
k2michelin
