The article reminds that taxes from Roth conversions completed by December 31 are due on January 15 of the following year. If retirees have not made quarterly estimated tax payments, penalties for underpayment may apply, even if the tax return has not yet been filed. To avoid penalties, retirees with an adjusted gross income (AGI) exceeding $150,000 typically need to prepay 110% of the previous year's tax liability to meet the "safe harbor" rule. By requesting tax withholding from an IRA account in November or December, payments can be retroactively allocated to all four quarters, thereby making up for earlier underpayments, whereas an estimated payment made in January only covers the fourth quarter. Furthermore, Roth conversions are irrevocable after December 31, and it is not advisable to pay taxes from the converted amount, especially for individuals under 59½, as this could result in an additional 10% early distribution tax.