there are exceptions to an underpayment penalty.
1) withholding and timely estimated tax payments = 90% of 2020 tax or
2) withholding and timely estimated tax penalties = 100% of 2019 tax (110% if adjusted gross income for 2019 was over $150,000
3) 2020 tax less withholding is less than $1000
state tax laws will vary from the above
this means for federal purposes if you meet any of the 3 exceptions above, you could owe a substantial amount come 4/15/2021 and not be hit with underpayment penalties.
