When the seller doesn't collect sales tax on a taxable item purchased from the Internet or mail order catalog, such as clothing, electronics, appliances or other tangible property, it is the purchaser's responsibility to report and pay use tax. Colorado state use tax is 2.9 percent. Consumers should also be aware that some local special districts in Colorado have use tax.

The Colorado Department of Revenue makes it easy to pay consumer use tax through its Revenue Online service. Click on the "Individual" button, then click on "File a Return" to "File Consumer Use Tax."