Mont. Code Ann. § 15-31-502 — Assessment And Payment Of Tax -- Estimated Tax Payment -- Amount Of Required Installments

15-31-502 . Assessment and payment of tax -- estimated tax payment -- amount of required installments. (1) All taxpayers shall compute the amount of tax payable under this chapter and shall remit the amount to the department of revenue on or before the 15th day of the 5th month following the close of the tax period.
(2) (a) A corporation shall make estimated tax payments if its annual estimated tax is $5,000 or more. Subject to the due date provision in 15-31-111 (2)(b), the estimated payments must be made in installments, as follows, if the $5,000 threshold is met or exceeded:
(i) For a corporation taxed on a calendar-year basis: For the following required installments the due date is:
1st
April 15
2nd
June 15
3rd
September 15
4th
December 15
(ii) For a corporation taxed on a fiscal-year basis: For the following required installments the due date is:
1st
15th day of the 4th month
2nd
15th day of the 6th month
3rd
15th day of the 9th month
4th
15th day of the 12th month
(b) Except as provided in 15-31-510 , the amount of any required installment is 25% of the required annual payment. The required annual payment is the lesser of:
(i) 80% of the tax shown on the return for the tax year or, if a return is not filed, 80% of the tax for that year; or
(ii) 100% of the tax shown on the return of the corporation for the preceding tax year if the preceding tax year was a period of 12 months and if the corporation filed a return for that year.
(3) The application of this section to tax years of less than 12 months must be in accordance with rules adopted by the department.
(4) At the election of the corporation, any installment of the estimated tax may be paid before the date prescribed for its payment.