A. Three years from the due date of the original tax year return, including valid filing extensions.
B. One year from the final determination of the amended federal return or federal change, whichever is later, provided that the allowable refund is not more than the decrease in Colorado tax attributable to the federal change or correction.
C. Two years from the payment of an assessment, provided the amended return raises issues relating only to the prior assessment and the refund does not exceed the amount of tax paid on the prior assessment.
D. Two years from the filing of an amended Colorado return resulting in the payment of additional tax, provided that the current amended return raises issues relating solely to the prior amended return and that the refund does not exceed the amount of the tax payment made as a result of the prior amended return.Additional Colorado Tax Income Taxes Deadlines