Mail your Colorado state tax return to the Denver processing center

Colorado's Department of Revenue processes all individual state tax returns at a single mailing address in Denver. The address you use depends on whether you are enclosing a payment with your return.

If you owe taxes and are sending a check or money order, mail your return to: Department of Revenue, Denver, CO 80261-0013. If you are not enclosing payment—because you expect a refund, owe nothing, or are paying electronically—mail to: Department of Revenue, Denver, CO 80261-0012. The difference in the last four digits of the ZIP code routes your envelope to the correct processing unit and speeds up handling.

Paper returns typically arrive within five to seven business days of mailing from within Colorado. Returns from out of state may take one to two weeks longer. Do not mail your return to a local tax office or county assessor; those offices do not process individual returns.

Key Takeaways

  • Use ZIP code 80261-0013 if you are enclosing a payment with your return.
  • Use ZIP code 80261-0012 if you are not enclosing a payment or are paying by electronic transfer.
  • Both addresses are in Denver and are operated by the Colorado Department of Revenue.
  • Paper returns take five to seven business days to arrive in Denver from within Colorado, and longer from out of state.
  • E-filing your return avoids mailing altogether and typically processes within two to three weeks.

What to include with your mailed return

Include your completed Form 104 (the Colorado individual income tax return) and all required schedules. Attach any forms that support deductions or credits you claimed, such as Schedule A for itemized deductions or Schedule C if you reported self-employment income. Do not send original documents like W-2s, 1099s, or receipts unless the return instructions specifically ask for them.

Write your Social Security number or federal employer identification number clearly on the top right corner of the first page of your return. Include your current mailing address and a phone number where you can be reached. If you are enclosing a check, make it payable to "Colorado Department of Revenue" and write your Social Security number on the back of the check.

Use a standard envelope and first-class mail. Do not use certified mail or require a signature; the department does not track these and they slow processing. Keep a copy of your return and all supporting documents for your records for at least three years.

When to mail to avoid delays

The tax filing important date in Colorado is the same as the federal important date: April 15 for most taxpayers, or the next business day if April 15 falls on a weekend or holiday. Mail your return at least one week before the important date to may support it arrives on time. Returns postmarked on or before the important date are considered timely even if they arrive after April 15, so the postmark date matters, not the arrival date.

The Denver processing center receives the highest volume of mail in late March and early April. If you mail your return in early February or early March, it will likely be processed faster. Returns mailed after April 15 are considered late unless you have a valid extension; filing an extension (Form 107) moves your important date to October 15 but does not extend the time to pay taxes owed.

Alternatives to mailing a paper return

E-filing your return is faster and more reliable than mailing. You can file electronically through a tax software provider that is approved by the IRS and Colorado, or through a tax professional. Electronic returns are typically processed within two to three weeks, compared to four to six weeks for paper returns. The state charges no fee for e-filing.

If you use tax software, choose one that supports Colorado returns and follow the software's instructions to file electronically. The software will transmit your return directly to the state and provide you with a confirmation number. If you work with a tax professional—a CPA, enrolled agent, or tax preparer—they can file electronically on your behalf.

E-filing also reduces the chance of errors because the software checks your math and flags missing information before you submit. If you are due a refund, e-filing typically results in a faster refund than mailing a paper return.

What happens after you mail your return

Once the Denver processing center receives your return, staff scan it into the state's system and verify that all required information is present. If something is missing or unclear, the department will mail you a notice asking for the missing information. This process typically takes four to six weeks from the time your return is received.

If you are due a refund, the state will mail you a check or deposit the refund directly to your bank account if you provided banking information on your return. Refunds by mail typically arrive within four to eight weeks of processing. If you chose direct deposit, the refund usually arrives within two to three weeks.

If you owe taxes and did not pay with your return, the department will send you a bill with payment instructions. Pay the bill by the date shown to avoid penalties and interest. You can also pay online through the Colorado Department of Revenue website without mailing anything.

Frequently Asked Questions

What if I mail my return to the wrong address?

If your return reaches a different office, it will be forwarded to the Denver processing center, but this adds one to two weeks to processing time. To avoid this, double-check the address on the return instructions before you mail. If you realize you mailed to the wrong address, contact the Colorado Department of Revenue at 303-238-7378 to report it.

Can I mail my return to a local tax office instead of Denver?

No. Colorado has only one processing center for individual returns, located in Denver. Local offices and county assessors do not accept or process individual income tax returns. Always mail to the Denver address provided in the return instructions.

Do I need to use certified mail or a tracking service?

No. Use standard first-class mail. Certified mail and tracking services do not speed up processing and may actually cause delays because the department does not monitor signature confirmations. A regular postmark is proof that you mailed your return on time.

What if I cannot mail my return by April 15?

File Form 107 (Colorado Extension of Time to File) before April 15 to move your important date to October 15. The extension gives you more time to file but does not extend the time to pay taxes owed, so pay any estimated amount by April 15 to avoid penalties. You can file the extension by mail, electronically, or through a tax professional.

How do I know if my return was received?

If you e-file, you receive a confirmation number when ready. If you mail a paper return, you can contact the Colorado Department of Revenue at 303-238-7378 after four to six weeks to ask whether your return was received and processed. Have your Social Security number and the tax year ready when you call.