Next Monday is “Cyber Monday,” or the day that online retailers are hoping that you haven’t spent up your holiday budget just yet.

Last year consumers spent $3.45 billion in online purchases on Cyber Monday, the largest one-day online sales record in history, according to Fortune.

Not to be a Grinch, but the Colorado Department of Revenue would like to remind Colorado consumers that they will owe taxes if the online retailer from whom they shop does not collect them.

How you will know if you owe taxes? According to the Department of Revenue, at the time of purchase, online retailers must provide a “Transactional Notice” to Colorado consumers that notifies them the retailer will not pay state sales taxes on the purchase, and that the customer may owe that tax to the state.

State sales tax is 2.9 percent.

But then it gets tricky. Colorado cities, counties and special districts also collect taxes, and consumers are expected to pay those taxes as well.

In order to find out what taxes you owe, the Department of Revenue has Form DR 1002, available at Colorado.gov/Tax, that will help you figure out what taxes you owe and how much.

Those taxes should be paid when you file your income tax returns in April.

You can also pay those taxes by electronically filing a Consumer Use Tax Return in Revenue Online, the department’s online filing system, or by paper using the Consumer Use Tax Return (DR 0252) available on the Department’s website at Colorado.gov/Tax.

For more information, visit Colorado.gov/Tax/UseTax.