You didn't mention a Roth conversion before. For determining the underpayment penalty, withholding is treated a little differently from estimated tax payments, and it works to your advantage. If you have tax withheld from a Roth conversion anytime during the year, the withholding is treated as if it was paid evenly during the year, even if you do the conversion in December. So that will reduce the penalty a bit because the withholding is treated as if you paid it earlier in the year. It partially makes up for not having made the earlier estimated tax payments. If you have not done the conversion yet, and you are able to choose how much tax to have withheld, you could reduce your estimated tax payment and increase the tax withheld from the conversion by a corresponding amount. That would further reduce the penalty.