estimated 2021 payments after January 18, 2022

[rbrookefox]

I underpaid my 2021 estimated taxes but paid more than 110% of last year's taxes, so as I understand it I will not be liable for a corresponding underpayment penalty. I just discovered the under payment but given the date (after Jan. 18) I'm not allowed to make an additional estimated payment online for 2021. Should I send the payment in by mail even though I'm not likely to be assessed an underpayment penalty or am I missing something here? 

[Vanessa A · Accepted solution]

It won't change anything if you mail in the payment at this point.  At this point, you can just make the payment with your return. Filing and paying at the same time would be better as the mailed in check payment may not be posted by the time an electronic return would be processed. 

This would cause an issue with what you report on your return as estimated payments corresponding with what the IRS has for their records. 

[rbrookefox]

Thank you, Vanessa.