EST-I: Underpayment of Estimated Tax by Individuals, Estates, and Trusts (Form EST-I) (2024)
Montana · Montana DOR · Used for tax years 2024
Montana Form EST-I calculates interest on underpayment of estimated tax for individuals, estates, and trusts for 2024. It determines the required annual payment and includes short, regular, and annualized income installment methods for calculating underpayments and interest.
Who files this form
Individuals, estates, and trusts can use Form EST-I to check whether they owe interest for underpaying estimated tax for 2024 and to calculate that interest. The department generally figures the interest for you, and you should not include Form EST-I with your tax return.
The form lists these exceptions to estimated tax payments and underpayment interest:
- Your 2023 tax period covered 12 months and your Montana tax liability was zero.
- Your 2024 income tax liability after credits and withholding is less than $500. Complete Part I, lines 1 through 4, to check this.
- You are a nonresident or part-year resident who was not required to file a 2023 Montana income tax return.
- You retired and were at least age 62. This exception applies only in the retirement year and the following year.
- You became disabled in 2024 or 2025.
- At least two-thirds of your gross income comes from farming or ranching.
When it's due
For tax year 2024, the estimated tax installment due dates shown for calendar-year taxpayers are:
- April 15, 2024
- June 17, 2024
- September 16, 2024
- January 15, 2025
Fiscal-year filers must adjust these dates accordingly.
For the 2024 regular-method interest calculation, use the date you paid the underpayment or April 15, 2025, whichever is earlier.
What you'll need
Have these returns and payment details available to complete the form:
- Your 2024 Montana Form 2 or Form FID-3, showing tax liability, withholding, credits, and estimated payments.
- Your 2023 Montana return, showing tax liability after nonrefundable credits and any overpayment applied to 2024.
- The amounts and dates of your estimated tax payments and payments toward any underpayment.
- Your name and SSN, spouse information where applicable, or the estate or trust name and FEIN.
If using the annualized income installment method, you also need income, deductions, Montana additions and subtractions, and credit information for each period. Depending on your situation, you may need federal and Montana-source capital gain and income amounts.
How to file
Do not include Form EST-I when you file your tax return. The department generally calculates underpayment interest for you, but you can use this form to calculate it yourself.
If you calculate the interest, enter the result from Part II, line 6, or Part III, line 15, on:
- Form 2, Schedule IV, line 2; or
- Form FID-3, page 2, line 25.
Common mistakes
- Skipping Part I. Complete it before any other part of the form.
- Using amended-return amounts. If you file an amended return, use the amounts from your original return to figure the underpayment.
- Counting a prior-year overpayment again in Part II. Do not include it in Part II, line 1. It belongs in Part I, line 3c.
- Using the short method for unequal or late payments. These payments require the regular method.
- Applying a payment only to the period you designated. Payments first cover an underpayment from an earlier period.
- Annualizing only selected installments. If you use Part IV for one payment due date, you must use it for all payment due dates.
- Including excluded deductions in Part IV. Do not include a state income tax deduction. Estates and trusts must also exclude the federal Qualified Business Income Deduction.
Questions people ask
Can I owe underpayment interest even if I get a refund?
Yes. Interest is calculated separately for each installment due date. Paying enough later does not necessarily eliminate interest for an earlier underpayment, even if your return shows a refund.
When can I use the short method?
Your tax year must cover 12 full months, and you must either have made no estimated tax payments or have made four equal estimated payments by the required due dates.
What if my income varied during the year?
The annualized income installment method may lower or eliminate one or more required installments. Complete Part IV before Part III, and use the annualized method for every payment due date.
Where do I start when checking whether I owe interest?
Start with Part I. If line 4 is less than $500, stop: you do not owe underpayment interest. Also stop if line 6 is less than or equal to line 3.
Who can I contact with questions?
Call (406) 444-6900, or use Montana Relay at 711 for the hearing impaired.