Regulation 39-22-608. 
Due date for filing income tax returns and payments.
(1) 	Weekends and legal holidays. 
(a)	When an income tax filing due date falls on a Saturday, Sunday or a legal holiday, returns will be considered to have been filed on the due date if they are filed on the next Department of Revenue business day.
(b) 	The due date of any Colorado income tax return, associated tax payment, or extension payment for a tax year ending December 31 that is due on April 16 or April 17 under subparagraph (a), above, will be extended one day to coincide with the federal due date if the Internal Revenue Service has extended the federal income tax due date by one additional day due to the observance of Emancipation Day in the District of Columbia.  This one-day extension does not apply to wage withholding payments and quarterly estimated income tax payments.
(2) 	Extension of time to file income tax return. All taxpayers will be allowed an automatic six-month extension of time for filing their income tax returns. However, interest on any net tax liability due will be assessed and penalty may also be due if the taxpayer has not complied with regulation 39-22-621.2(j).