it's a combination of 1099-INT Box 3 (less any premium in Box 12, and less any other adjustments e.g. accrued interest - see note below), 1099-DIV Box 1 US Gov Obligations amount, 1099-OID Box 8 (less any adjustments). Note the AMD on 1099-B Box 1f for Treasury Notes transferred to Schedule B does NOT flow to VA as a subtraction (a whole other topic if it applies). Not sure if other situations apply but these are the main reasons for a subtraction from your Fed income.
there's no easy way to drill down from that number to see these figures from your 1099s, the only way I have found is to just go thru the 1099s to double-check everything until you identify the difference. It's usually a typo or some issue with the 1099, or error handling something like accrued interest.
If you do have accrued interest adjustment on the 1099-INT with multiple types of income then TT doesn't know how to allocate it across Box 1/3/8 and will pro-rata it, so you have to split the 1099 in TT if that is the case.
Folks have also reported various issues with imported 1099s not flowing correctly to state either for out of state muni additions to interest or subtractions for Us Gov. If you exhaust all possibilities and it just seems that a 1099 is simply not flowing correctly to state then the usual solution is to delete the 1099 and input it manually.
