Montana – Form EST-I – Underpayment of Estimated Tax

Article: 50573

Overview 

If you did not pay enough Montana income tax during the year through withholding or estimated payments, you may be subject to an underpayment penalty. To calculate and report this penalty, you will need to complete the Underpayment of Estimated Tax screen, which corresponds to Montana Form EST-I. 

Who Needs to Complete Form EST-I? 

You may be required to file Form EST-I if: 

• You owe more than $500 in tax after subtracting withholding and credits. 

• Your total payments (withholding + estimated payments) were less than 90% of your current year tax liability or 100% of the prior year’s tax liability (safe harbor rule). 

• Your estimated payments were late or made unevenly, and you want to reduce or calculate the penalty using the annualized income method. 

• You want to request a waiver due to special circumstances (e.g., casualty, disaster, unusual income fluctuations). 

Note: You can avoid the penalty altogether if you meet one of Montana’s safe harbor provisions. Otherwise, the EST-I form is required to calculate the amount of interest owed. 

How to Report 

1. Navigate to the State Taxes section on the left-hand side of the screen. 

2. Click the link: I’d like to see the forms I’ve filled out or search for a form. 

3. In the dropdown menu, select Montana. 

4. Click on the Other tab. 

5. Select Underpayment of Estimated Tax to open the screen. 

6. Enter all applicable information.  

7. Click Save once complete. 

Additional Resources 

For further guidance, see:  

2024 Montana Form 2 Individual Income Tax Instructions (PDF) 

2024 Montana Form EST-I – Underpayment of Estimated Tax (PDF)