"My estimated taxes were fully paid in December 2023. The amount paid was exactly equal to the tax due and paid in 2022"
TurboTax calculated the penalty correctly. Because income is by default treated as received equally throughout the year and the US tax system is pay as you go, making a single estimated tax payment in December to cover your entire year's tax liability will not avoid underpayment penalties for tax quarters 1 through 3. It will only eliminate the underpayment penalty for Q4.
You might be able to reduce the penalties for Q1 through Q3 by annualizing income on Schedule AI of Form 2210. Unless all of your income was received in Q4, you'll still have underpayment penalties for earlier quarters, but they might be reduced. However, if the bulk of your income was received in Q1, annualizing income will instead increase the total penalty.
This answer has been verified for accuracy by an Intuit expert employee
