Assuming this is for 2018 taxes:
You'd have to look at a printout of your Federal and NC tax returns to see what you might have missed on the NC-side. Most income just transfers over directly from the Federal to the appropriate NC places, but in certain situations, you may have removed some income from the NC part accidentally.....either with some mis-entry on the Federal side, or some income allocations in the NC section (if you were a part-year resident of NC, or a non-resident of NC in 2018)
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1) For a full-year NC resident for 2018 you might have accidentally taken out some Retirement income from NC income that wasn't eligible to be NC-exempt.
2) If you were a part-year resident or Non-resident of NC for 2018, then you might not have assigned some income to NC that should have been NC taxable.
3) Could be something else too...but tah is all guessing at this point.
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If the NC letter doesn't describe exactly where they think you under-reported, look for a telephone number on the letter to call the NC Dept of Rev directly and see if they can describe exactly what income they think you under-reported....BUT...Have your Federal and NC printouts right in front of you before you call.
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*
