@BillM223 Yes, my 2021 return has Form 8959. And yes, Line 11 of Schedule 2 (1040) shows a few thousand dollars (the same amount as what's shown on Line 7 of Form 8959).
This seems bizarre (or rather unfair) to me. To avoid any tax underpayment penalty for tax year 2022, I need my 2022 paycheck withholdings + 1040-ES payments to be at least 110% of 2021's tax liability. In calculating 2022's paycheck withholdings, Additional Medicare Tax is not included. Yet, in calculating 110% of 2021's tax liability, the Additional Medicare Tax from 2021 (Line 11 of Schedule 2) is included.
