Colorado state income taxes are due April 15 of the year after the tax year. The state grants an automatic six-month extension to October 15 if you need more time to file, but that extension covers only the paperwork. Any tax you owe still has to be paid by April 15, and you need to pay at least 90 percent of your total liability by that date to avoid a late-payment penalty.1Department of Revenue – Taxation. Individual Income Tax – Due Dates and Filing Extension
The April 15 Filing Deadline
Your Colorado individual income tax return (Form DR 0104) is due April 15 of the year following the tax year. If April 15 falls on a Saturday, Sunday, or legal holiday, the deadline moves to the next business day.1Department of Revenue – Taxation. Individual Income Tax – Due Dates and Filing Extension
You have to file a Colorado return if you were a full-year or part-year resident, or a nonresident who earned income from Colorado sources, and you are required to file a federal return or have a Colorado tax liability.2Department of Revenue – Taxation. Individual Income Tax – Filing Requirements
The Automatic Extension to October 15
If April 15 is going to come and go before your return is ready, Colorado gives you until October 15 automatically. No form, no request, no approval. Colorado Regulation 39-22-608 grants the six-month extension to every taxpayer.3Cornell Law Institute. Colorado Code 39-22-608 – Due Date for Filing Income Tax Returns and Payments
The catch is that the extension only moves the filing deadline. It does not move the payment deadline. You still have to pay at least 90 percent of your total tax liability by April 15. Hit that 90 percent mark and any remaining balance will accrue interest but no penalty. Fall short and the penalty kicks in on the unpaid portion.1Department of Revenue – Taxation. Individual Income Tax – Due Dates and Filing Extension
If you want to send an extension payment by check or money order, use Form DR 0158-I. Only file the form if you are actually making a payment with it; if you owe nothing or you are paying electronically, skip it.4Colorado Department of Revenue. DR 0158-I – Extension Payment for Colorado Individual Income Tax Instructions Electronic extension payments can also be made through Revenue Online.
Quarterly Estimated Tax Deadlines
If you have income that is not subject to Colorado withholding — self-employment earnings, freelance pay, rental income, investment gains — you are expected to make quarterly estimated payments through the year. The four due dates are:
- 1st quarter: April 15
- 2nd quarter: June 15
- 3rd quarter: September 15
- 4th quarter: January 15 of the following year
The same weekend-and-holiday rule applies: if a due date lands on a Saturday, Sunday, or holiday, the deadline rolls to the next business day.5Cornell Law Institute. Colorado Code 39-22-605 – Estimated Individual Income Tax Farmers and fishers follow a different schedule, with a single estimated payment due by January 15.
Safe Harbor for Estimated Payments
You can avoid an underpayment penalty even if your estimated payments turn out to be short of your actual liability, as long as you meet one of two safe harbors. If your prior-year adjusted gross income was $150,000 or less ($75,000 or less if married filing separately), your estimated payments for the current year need to add up to at least 100 percent of last year’s tax. If your prior-year AGI was above $150,000, the threshold rises to 110 percent of last year’s tax.6Colorado Secretary of State. Rules Concerning Estimated Tax Payments Miss both and the penalty is calculated on the shortfall for each quarter.5Cornell Law Institute. Colorado Code 39-22-605 – Estimated Individual Income Tax
What Happens if You File or Pay Late
Colorado charges penalties for late filing, late payment, or both. The penalty is the greater of $5 or 5 percent of the unpaid tax, plus an additional 0.5 percent for each full or partial month the tax remains unpaid, up to a maximum of 12 percent.7Department of Revenue – Taxation. Tax Topics – Penalties and Interest
Interest starts running on any unpaid balance the day after April 15, even if your filing extension is valid. For calendar year 2026, the Department of Revenue charges a discounted annual interest rate of 8 percent if you pay the tax before you receive a notice of deficiency or within 30 days of receiving one. Miss that window and the regular rate of 11 percent applies.8Colorado.gov. Tax Topics – Penalties and Interest
So if you cannot finish the return by April 15, pay what you can anyway. Paying at least 90 percent of your eventual liability by that date wipes out the penalty, and you will only owe interest on what is left.1Department of Revenue – Taxation. Individual Income Tax – Due Dates and Filing Extension
PTC Rebate Deadlines Are Different
The Property Tax/Rent/Heat (PTC) Rebate for low-income seniors, surviving spouses, and people with disabilities runs on its own calendar, not the April 15 cycle. The 2024 PTC Rebate application is due December 31, 2026, and the 2025 rebate application is due December 31, 2027. Starting with the 2025 tax year, individuals with disabilities under age 65 and surviving spouses under age 58 will need to file a regular Colorado income tax return to receive the benefit instead of applying separately.9Department of Revenue – Taxation. Property Tax/Rent/Heat Credit (PTC) Rebate
Amended Return Deadlines
If you catch a mistake on a return you have already filed, you fix it with Form DR 0104X. There is no fixed deadline to file an amendment itself, but two timing rules matter.
First, if the IRS adjusts your federal return, you have to file a Colorado amended return within 30 days of receiving the IRS notice.10Department of Revenue – Taxation. Amending an Individual Income Tax Return
Second, if you are amending to claim a refund, the general statute of limitations is four years from the original due date of the return, or three years from your last tax payment for that year, whichever is later. Wait longer than that and the refund is lost even if the return itself is correct.