So, given all that, do I have any recourse to avoid paying the almost $400 in underpayment penalty? I don't think you have reasonable cause to justify a waiver.
There is something you can do that might lower your penalty. there's an option to use actual withholding for each period. you would check box D on the 2210 and enter your withholding for each period specified. The default used by Turbotax to figure your penalty, is 1/4 of your withholding is deemed to occur each period.
If that does not work there is the AI method.
for 2025 there are two safe harbors that would likely apply
1) 2025 withholding and timely estimated tax payments = > 90% of 2025 tax (each estimate = 22.5% of 2025 tax less withholding for the 2025 period) almost impossible to know on a timely basis
2) 2025 withholding and timely estimates => 110% of your 2024 tax ( each estimate = 27.5% of 2024 tax less withholding for the 2025 period). The alternative for each estimate if you know what your withholding will be for all of 2025 is (110% 20204 tax less withholding for 2025) divided by 4.
paying estimates is voluntary, but failure to have enough withheld to meet either safe harbor results in underpayment penalties.
