Form EST-I – Underpayment of Estimated Tax by Individuals, Estates, and Trusts

Form EST-I is used by individuals, estates, and trusts to calculate whether they underpaid estimated taxes during the tax year. Taxpayers who expect to owe $500 or more in income tax (after subtracting withholding and credits) must make estimated payments throughout the year. If these payments are late or insufficient, interest may apply.

While taxpayers may choose to include the amount owed on their income tax return, the Montana Department of Revenue automatically calculates the underpayment interest amount. Filers do not need to include Form EST-I with their return unless they prefer to calculate the interest themselves.

The form is helpful for individuals, estates, and trusts, and their tax professionals who would like calculate interest on the underpayment of estimated taxes on their own.