NOTE: The following applies to users who will be paying quarterly Colorado estimated taxes in 2025.
I think that the 2024 TurboTax calculation of the Colorado quarterly estimated tax payment is incorrect.
During Step-by-Step, if user selects "100% (110%) of 2024 taxes", which is the default option, it appears to use the current year's CO tax (Form 104, line 12) less the TABOR State Sales Tax Refund amount (Form 104, line 35).
However, the Colorado Individual Income Tax Guide (link below) specifically says to exclude the "Sales tax refund credit" (Part 7. "Estimated Tax Payments: Net Colorado tax liability") when calculating the estimated tax amount. This makes some sense, because the actual TABOR sales tax refund changes from year to year, and is not released until around mid-October.
https://tax.colorado.gov/individual-income-tax-guide Note that this is not the same document as the "104 Book" that contains forms and line-by-line instructions. Caveat: the CO Guide also lists other exclusions which may or may not apply to a given user; I did not check to see how TurboTax handles those other exclusions.
What this means is that if you use TurboTax's 2025TY CO estimated tax calculation, you will be paying less each quarter than you should be. This can be verified by adding the Tabor sales tax refund amount to the amount on the TurboTax CO Estimated Tax Worksheet, Part 1, line 1a. The resulting amount should match Form 104, line 12.
Whether the amount of the quarterly estimated tax underpayment is important will depend on each user's individual tax situation. You could always increase your estimated tax payment each quarter and just amend the amount shown on that quarter's voucher.
This was still an issue in TurboTax as of 4/9/2025. Also note that I'm not a tax expert - am just reporting what I found while checking my return.
cc: @KrisD15
