Why am I paying Colorado estimated taxes this year when I didn't last year when I filed without Turbotax?

TurboTax usually includes 4 quarterly vouchers with your printout if you didn't withhold or pay enough tax each quarter and/or year. The program does this to avoid a possible underpayment penalty on next year's taxes. However, you're not required to make estimated tax payments; it's a suggestion based on the info in your return.

Per CO State Estimated Individual Income Tax Payment Vouchers booklet (104EP):

General Rule

In most cases, you must pay estimated tax if you expect to owe more than $1,000 in net tax for 2018, after subtracting any withholding or credits you might have.

Required Payments

The required annual amount to be paid is the smaller of:

• 70% of the actual net Colorado tax liability, or
• 100% of the preceding year’s net Colorado tax liability. This rule only applies if the preceding year was a 12-month tax year, the individual filed a Colorado return, and the federal adjusted gross income on that return was $150,000 or less (or, if married filing separately, $75,000 or less), or
• 110% of the preceding year’s net Colorado tax liability. This amount applies only if the preceding year was a 12-month year, and the individual filed a Colorado return.

Please feel free to review the following link(s) and the link(s) embedded on the webpage(s) for more information:

• Why did 1040-ES estimated tax vouchers print out? Do I need them?
  
• Why am I getting an underpayment penalty if I'm getting a refund?
• What are estimated taxes?
• Do I need to make estimated tax payments to the IRS?
• Estimated Taxes - How to Determine What to Pay and When