Colorado 2014 tax interest and penalty rates for all state and state-collected taxes are noted in the publication FYI General 11, “Colorado Civil Tax Penalties and Interest.” The rate of 6% will apply to underpayments, nonpayments, and overpayments of Colorado taxes during 2014. For example, the rates will apply to 2013 income tax, which is due in 2014.
If payment of the tax, or an agreement to pay, is made within 30 days of notice of underpayment or nonpayment,or a tax underpayment or nonpayment is paid voluntarily without notification from the Colorado Department of Revenue, the CDOR waives the three percentage points above the prime rate and the applicable rate is 3%.
The annual interest rate is the prime rate in July of the preceding year, as reported by The Wall Street Journal , plus three percentage points rounded to the nearest full percent.
The Colorado rates have not changed since 2010.