Proconnect doesn’t calculate the Utah tax penalty the same way that the Utah State tax commission does. I just got a late payment notice from Utah that charged a 10% penalty ($4,000 on $40,000 tax) for a return filed on 4/14 but not paid until 6/1. Proconnect only calculated a $20 FTP penalty.

BTW I worked for a previous firm that used UltraTax and they calculated it differently too.

I called the both the Utah Tax Commission and UltraTax and they both insisted that they were doing it right. Coincidently shortly after I called, Utah took down their penalty calculator on their website.

For anyone who is interested here are the Utah rules from Pub 58.

We may assess a late payment penalty for payments you make after the due date.

To avoid a late payment penalty you must pay all tax due before the return due date, or pay all tax, interest and penalties:

1. within 90 days of the due date with a late filed return,
2. on the same day an amended return is filed, or
3. within 30 days of an audit assessment. See number 5 under Penalty Detail, below.

The late payment penalties are as follows:

1.Return filed by due date but underpaid; or extension return filed but tax underpaid on original due date:

1. Return filed after due date and not paid in full within 90 days of due date: