I had a refund, paid four equal payments of estimated tax, yet Turbotax calculated that I had an underpayment penalty. Turbotax's error was it did not provide a provision to use the appropriate Optional method on the form MN15. The way I got around it was zeroing out the line 21 amounts from my 2018 and 2019 returns. This was disappointing particularly since that information was already entered and Turbotax was not able to account for it. Secondly, this came to lite only after I paid to electronically file my MN return, and then told I couldn't because MN did not accept electronic filing if a penalty was included, but rather I would have to file by mail.
