How to Pay Colorado State Income Tax and What Happens If You Don't
How Colorado collects state income tax from you
Colorado takes state income tax through two main routes: withholding from your paycheck if you work as an employee, or direct payment if you're self-employed or have income that doesn't get withheld. The state uses the same federal tax year—January 1 through December 31—and the same filing deadline: April 15, unless that falls on a weekend or holiday.
If you're an employee, your employer sends Colorado a portion of each paycheck based on the W-4 form you filled out. That money goes into an account held by the state until you file your return. If too much was withheld, you get a refund. If too little was withheld, you owe the difference when you file. Self-employed people and those with investment income usually need to send quarterly estimated tax payments to avoid a large bill at tax time.
Colorado's income tax rate is flat: 4.40% as of 2024, applied to your federal taxable income. This rate can change year to year, so check the Colorado Department of Revenue website before you file to confirm the current rate.
Key Takeaways
- Colorado collects income tax through paycheck withholding for employees and quarterly estimated payments for self-employed people, with the same April 15 deadline as federal taxes.
- You file your Colorado return using Form 104, which you can submit by mail, electronically through the state's system, or through a tax software provider.
- If you owe Colorado income tax, you can pay online through the Department of Revenue website, by mail with a check, or through your tax software.
- Penalties for late payment start at 5% of the unpaid tax and increase the longer you wait, plus interest that compounds daily.
- If you cannot pay in full by April 15, you can request a payment plan directly from the Department of Revenue, which may reduce penalties.
Where and how to file your Colorado return
You file your Colorado state return using Form 104, the Colorado Individual Income Tax Return. You need this form whether you owe tax, expect a refund, or break even. The form asks for your federal taxable income, Colorado-specific deductions, and credits you may be may have access to to.
You have three filing methods. The first is electronic filing through the Colorado Department of Revenue's website at tax.colorado.gov—you can file directly there if your return is simple, or you can use approved tax software (TurboTax, H&R Block, TaxAct, and others all support Colorado). The second is paper: print Form 104, fill it out by hand, and mail it to the address listed on the form. The third is through a tax professional or CPA. Electronic filing is fastest and reduces errors; the state processes e-filed returns in two to four weeks if there are no issues.
You must include your federal return with your Colorado return if you file by mail. If you file electronically, you don't send the federal return separately, but you do need to have it completed first so you can reference the numbers.
Paying Colorado income tax when you file
If your withholding or estimated payments didn't cover your full tax bill, you owe the difference by April 15. The state offers several payment methods. Online payment through tax.colorado.gov is the fastest and most direct—you can pay by bank transfer (ACH) or debit card, and the payment posts within one business day. Paying online also gives you a confirmation number immediately, which serves as proof of payment.
You can also pay by check or money order mailed with your paper return. Write your name, address, Social Security number, and tax year on the check, and mail it to the address on Form 104. Payment by check takes longer to process—typically five to seven business days after the state receives it—so if you're close to the deadline, pay online instead.
If you use tax software to file, most platforms offer a payment option at the end of the filing process. The software routes your payment to the state and includes it with your return electronically. This method is reliable but charges a small fee (usually $2 to $5) that the software company keeps.
What happens if you don't pay by April 15
Colorado charges a failure-to-pay penalty starting at 5% of the unpaid tax amount, applied on the first day after the deadline. The penalty increases by 5% for each additional month the tax remains unpaid, up to a maximum of 25%. So if you owe $1,000 and pay 30 days late, you owe $1,050 in tax plus interest. If you pay 60 days late, you owe $1,100 in tax plus interest.
On top of the penalty, Colorado charges interest on the unpaid tax. The interest rate is set quarterly and compounds daily. As of early 2024, the rate is 8% per year, but it changes based on federal rates. Interest accrues from April 16 (the day after the deadline) until you pay, regardless of whether you've filed your return.
If you file your return late but pay by April 15, you avoid the failure-to-pay penalty but still owe interest on any tax that was unpaid as of April 16. If you both file and pay late, both penalties apply.
Setting up a payment plan if you can't pay in full
If you cannot pay the full amount by April 15, contact the Colorado Department of Revenue before the deadline to request an installment agreement. You can reach them at 303-238-TAXCO (8296) or through their website. The state will work with you to set up a payment schedule based on what you can afford.
An installment agreement does not erase the penalties and interest you owe, but it can reduce the failure-to-pay penalty if you enter the agreement before April 15. The state typically charges a setup fee (currently $225 for a standard agreement) and requires you to pay a portion of the tax upfront. Payments are usually due monthly, and the agreement specifies the exact dates and amounts.
If you set up a plan and miss a payment, the agreement can be cancelled and the full unpaid balance becomes due immediately. The state will send you a notice before they cancel, so contact them right away if you know you'll miss a payment—they may modify the plan rather than terminate it.
Refunds and what to do if Colorado owes you
If your withholding or estimated payments exceeded your actual tax bill, Colorado owes you a refund. The state processes refunds in the order returns are received. If you filed electronically, expect your refund within two to four weeks. If you filed by mail, add another week or two for processing time.
You can choose to receive your refund by direct deposit to your bank account (fastest, usually five to seven business days after the state approves it) or by check mailed to your address (two to three weeks). When you file, you'll select which method you prefer. Direct deposit requires your routing number and account number, which you can find on a blank check or by calling your bank.
If you don't receive your refund within the expected timeframe, check the status on tax.colorado.gov using your Social Security number and the amount of the refund. The state's website shows whether your return is still being processed, approved, or sent out.
Self-employed and quarterly estimated tax payments
If you're self-employed or have income that doesn't get withheld—such as rental income, investment gains, or freelance work—you're expected to send Colorado quarterly estimated tax payments. These payments are due on April 15, June 15, September 15, and January 15 of the following year. The state uses these payments to collect tax throughout the year rather than waiting until April 15.
To calculate your quarterly payment, estimate your total income for the year, subtract deductions, apply the 4.40% tax rate, and divide by four. If your income changes during the year, you can adjust future payments. You can pay quarterly estimates online through tax.colorado.gov, by check mailed to the Department of Revenue, or through tax software.
If you don't make quarterly payments and owe a large amount on April 15, you'll face penalties and interest on the unpaid balance. However, if you pay at least 90% of your current year tax or 100% of your prior year tax through quarterly payments, you can avoid the underpayment penalty even if you owe a small amount when you file.
Frequently Asked Questions
Can I file my Colorado return before I file my federal return?
No. Colorado requires your federal return to be complete first because the state uses your federal taxable income as the starting point. You can prepare both at the same time, but you must file federal first, then Colorado. If you file Colorado before federal and the IRS later adjusts your federal return, you'll need to file an amended Colorado return.
What if I moved out of Colorado during the year?
You owe Colorado income tax only on income earned while you were a resident. When you move, you become a part-year resident. File Form 104 and indicate the date you moved on the return. Colorado will calculate your tax based on the portion of the year you lived there. You may also owe tax to the state you moved to, so check that state's rules.
Do I have to file a Colorado return if I don't owe anything?
If you had Colorado income tax withheld from your paychecks and expect a refund, you must file to claim it. If you had no withholding and no tax liability, you're not required to file. However, filing ensures you receive any refund you're may have access to to and keeps your tax account current with the state.
What if I can't find my Social Security number or tax documents?
Contact the Colorado Department of Revenue at 303-238-TAXCO (8296) before April 15. They can help you locate your account and may be able to extend your deadline if you're missing documents due to circumstances beyond your control. Have your name, address, and date of birth ready when you call.
Can I pay Colorado taxes through my employer's payroll system?
No. Employers send Colorado withholding to the state automatically; you don't make separate payments. If you want to increase withholding to avoid owing at tax time, update your W-4 form with your employer, and they'll adjust future paychecks. This is different from making a direct payment to the state.