Estimated tax is the method used to pay tax on income that is not subject to withholding. Wages typically have withholding, but earnings from self-employment, interest, dividends, rents, etc. would be subject to estimated tax. You might also pay estimated tax if your withholdings are not enough to be excluded from the General Rule. If you file federal Form 1040-ES with the federal Internal Revenue Service (IRS), typically you would pay estimated tax to the Colorado Department of Revenue.
General Rule: In most cases, you must pay estimated tax if you expect to owe more than $1,000 in net tax for 2023, after subtracting any withholding or credits you might have.