MARCH
15th	File calendar year corporation Federal returns and Montana S-corporation (Federal Forms 1120 or 1120S and Montana Form CLT-4S as applicable) or file for an automatic six-month extension (Federal Form 7004 or Montana PT-EXT). For fiscal year-end corporations, returns are due by the 15th day of the third month following the close of your tax year.
APRIL
15th	Deposit the first estimated tax payment for calendar year corporations.
MAY
15th	File Montana State Corporation Income Tax Return (Montana Form CLT-4) or make a tentative payment if tax is due on Form CT. No extension is necessary.
JUNE
15th	Deposit the second estimated tax payment for calendar year corporations.
SEPTEMBER
15th	Deposit the third estimated tax payment for calendar year corporations.
15th	File extended calendar-year corporation returns (Federal Form 1120 or 1120S and Montana S-corporation Information Return on CLT-4S).
NOVEMBER
15th	File extended calendar-year Montana Corporation Income Tax Return on Form CLT-4.
DECEMBER
15th	Pay the fourth estimated tax payment for calendar-year corporations.
31st	Last day for charitable contribution to be eligible on your tax return. Accrual basis "C" corporations may have extra time under certain conditions.
NOTE!	Estimated tax payments for corporations with a fiscal year-end are due as follows:
	First quarter estimated tax payment: 15th day of the fourth month following the close of your tax year.
	Second quarter estimated tax payment: 15th day of the sixth month following the close of your tax year.
	Third quarter estimated tax payment: 15th day of the ninth month following the close of your tax year.
	Fourth quarter estimated tax payment: 15th day of the twelfth month following the close of your tax year.