Mail your Colorado tax return to the Denver processing center

Colorado tax returns go to a single mailing address in Denver. The Colorado Department of Revenue processes all individual income tax returns at one location, regardless of whether you owe money, expect a refund, or are filing an amended return. The address depends on whether you are enclosing a payment.

If you are sending a payment with your return, mail it to: Colorado Department of Revenue, P.O. Box 17087, Denver, CO 80217-0087. If you are not sending a payment — because you expect a refund or owe nothing — mail it to: Colorado Department of Revenue, P.O. Box 17088, Denver, CO 80217-0088. Using the correct box number helps the department sort returns faster.

Returns typically arrive within five to seven business days of mailing. The department does not confirm receipt by mail, so keep a copy of your return and any payment documentation for your records.

Key Takeaways

  • Colorado has one mailing address for all individual returns, located in Denver, with two different P.O. boxes depending on whether you are sending a payment.
  • Use P.O. Box 17087 if your return includes a check or money order; use P.O. Box 17088 if you are not sending payment.
  • Mail your return using regular first-class mail; Colorado does not require certified mail or tracking.
  • Keep a copy of your return and proof of mailing in case questions arise about whether the return was received.

What to include with your payment

If you owe Colorado income tax, write a check or money order payable to "Colorado Department of Revenue." Do not send cash. Write your Social Security number and "Colorado Income Tax Return" on the front of the check so the payment is matched to your return correctly.

Include the check inside the envelope with your completed return form. Do not mail the check separately. The department processes returns and payments together, and a separate check can cause delays in crediting your account.

Mailing important date and timing

Colorado follows the federal tax important date: April 15 for most taxpayers. If April 15 falls on a weekend or holiday, the important date moves to the next business day. A return is considered on time if it is postmarked by the important date date, even if it arrives in Denver after April 15.

Mail your return at least one week before the important date to account for postal delays. If you cannot meet the important date, you may file an extension with the federal government, which also extends your Colorado important date. An extension gives you until October 15 to file, but does not extend the important date to pay taxes owed — interest and penalties accrue on unpaid tax from April 15 forward.

When to use electronic filing instead

The Colorado Department of Revenue encourages electronic filing through the federal IRS system. E-filing is faster, reduces errors, and you receive confirmation that your return was received. Most tax software (TurboTax, H&R Block, TaxAct) allows you to file both your federal and Colorado returns electronically in one step.

E-filed returns are processed within two to three weeks, compared to four to six weeks for mailed returns. If you are due a refund, e-filing also speeds up the refund by several weeks. You do not need to mail a paper return if you file electronically.

Amended returns and corrections

If you need to correct a return you already filed, mail an amended Colorado return (Form 104-X) to the same Denver address: P.O. Box 17087 if you are sending a payment, or P.O. Box 17088 if you are not. Write "AMENDED" clearly at the top of the form so the department knows it is a correction, not a duplicate filing.

The department processes amended returns in the order they are received, which can take eight to twelve weeks. If you are owed a refund from the amendment, the department will mail it to the address on file. If you owe additional tax, include a check with the amended return.

What happens after you mail your return

Once the department receives your return, it is scanned and entered into the system. You will not receive a mailed confirmation. If you filed electronically, you will see an acceptance notice within 24 hours. If you mailed a paper return, you can check the status of your return on the Colorado Department of Revenue website after four to six weeks by entering your Social Security number and filing status.

If the department has questions about your return, it will contact you by mail at the address on your return. Responses are usually requested within 30 days. If you are due a refund and no issues are found, the refund is mailed to your address on file within six to eight weeks of receipt.

Frequently Asked Questions

Can I mail my Colorado return to a different address?

No. The Denver P.O. boxes are the only addresses the Colorado Department of Revenue accepts for mailed returns. Sending your return to any other address will delay processing or result in the return being returned to you.

What if I mail my return to the wrong P.O. box?

If you send a payment to P.O. Box 17088 (the no-payment box) or vice versa, the return will still be processed, but it may take longer because staff will need to sort it manually. To avoid this, double-check the box number before sealing your envelope.

Do I need to send my return certified mail?

No. Regular first-class mail is sufficient. The postmark date is what matters for the important date, not the delivery method. Certified mail is not necessary unless you want proof of mailing for your own records.

How do I know if my mailed return was received?

You can check the status on the Colorado Department of Revenue website after four to six weeks. You will need your Social Security number and filing status. If you want when ready confirmation, e-filing is a better option because you receive an acceptance notice within 24 hours.

What if I owe money but cannot pay by April 15?

Mail your return by the important date even if you cannot pay the full amount. The department assesses penalties and interest on unpaid tax, but filing on time reduces the penalty. You can contact the Colorado Department of Revenue to discuss a payment plan for the amount owed.