Yes, a penalty may be assessed when you pay less than 90% of your tax liability during the tax year. The standard penalty is 3.398% of your underpayment, but it gets reduced slightly if you pay up before April 15. If you received premium assistance through advance payments of the PTC in 2020, and the amount of advanced exceeded the amount of PTC you can take, you could be subject to a penalty for underpaying your estimated tax.
