Have you entered the estimated taxes for the fourth quarter? Typically, the underpayment penalty calculation divides your withholding into equal amounts for each quarter. If you had sufficient taxes withheld from your pension distributions, each quarter should have no tax due. But if you haven't entered the estimated tax payment for the IRA distribution, the annualized method won't work.
Also, the calculations on Form 2210AI use a ratio of each quarter's income to the total for the year, then subtract those amounts from the total to arrive at your 4th quarter income. This is why there is no entry for quarter four. The total tax due for each quarter is matched with the allocated withholdings plus any estimated tax payments.
If you are using TurboTax for desktop, you can follow these calculations on the actual forms using Forms Mode. But if you are using TurboTax Online, you would need to either pay for your return first (to print out the forms you need) or purchase TurboTax for Desktop and export a copy of your online return.
Your final option is to upgrade to TurboTax Live so that a tax expert can walk through your return with you.
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