I did make estimated payments throughout the year in addition to withholding on SS and pensions. Form MN M15 is prepopulated with data that I am unable to change.
Please see below for information on why you are getting an underpayment penalty.
If you would like to contact customer support for additional assistance please see below.
https://ttlc.intuit.com/community/using-turbotax/help/what-is-the-turbotax-phone-number/00/25632
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.
@LukeMN It is still possible to have an underpayment penalty: if you don't pay the estimated payments on time. And you are correct that all of this can be affected by alternative methods of calculating the amount of payment that needed to be made by the quarterly payment deadline. But double-check everything, including your entries, to make sure your inputs are correct, and then, if they are, you may wish to contact customer service to resolve the processing issue you are experiencing. The following link has more information: How do I contact TurboTax?