IF you didn't pay it with your actual tax filing, then the IRS and state will send their own letters in the next few months.
Look at your tax form printouts...
Federal: Line 23 of your Federal form 1040 shows the penalty already applied if you are already paying the IRS
NC: Lines 26 b,c,d,or e of your Form D-400 will show any penalties or interest already included in your NC tax return.
Of course, these penalties and interest depend on exactly what dates the IRS and State actually get the payments you make for your final taxes owed...so if you do owe them, make sure you pay promptly (or have already arranged the direct Debit) . They may still send an extra billing letter for more $$ in a few months if you don't pay promptly.
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(It's more rare, but possible to owe a penalty, even if you get a refund...but in that case, the penalty and interest is calculated based on when the tax authorities accept your tax file...and that may vary somewhat from any calculation done in your tax submissions)
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*
