In the US, the Christmas season usually tips off after Thanksgiving, but as retailers grow more aggressive in taking on e-commerce, they are introducing holiday promotions and advertising for the holiday season as early as September—a phenomenon the industry pegs the Christmas creep.

The growing prevalence of this trend continues to impact retailers’ sales during the holiday season, devaluing one-day big hitters like Black Friday and Cyber Monday that both physical and e-commerce stores count on for profits. Some retailers make up a third of their total annual sales during the holiday season, buoyed by these national one-day events.

That’s according to Cushman & Wakefield’s e-commerce and electronic fulfillment practice group lead Ben Conwell and C&W director of retail research in the Americas Garrick Brown. The two hosted a webcast this week discussing national retail trends for the holiday season—particularly e-commerce’s continued impact on the industry.

“The diminished importance of Black Friday is just striking, and there are a couple of things you can attribute it to. Part of it is the Christmas creep,” Garrick says. “The Christmas holiday season is being stretched out and diminishing the importance of any one day for brick-and-mortar.”

The Christmas creep is all about holiday promotions and markdowns, and Cushman & Wakefield data says 16% of retailers are marking down prices as early as September, while 46% are introducing holiday promotions before Nov. 1 and 54% start marking down prices after Nov. 1.

“We’ve seen television ads for Amazon already promoting their Black Friday sales going into effect today (Nov. 16),” Ben says. “And eBay is flying the airwaves hard with promotional 'buy now, shop now' to avoid this Christmas creep.”

Both experts say this trend is here to stay, and project this year’s holiday sales will increase by 3.7%. Though e-commerce accounted for only 8.1% of total retail sales in Q2 (not including automotive and fuel sales), the C&W experts say not to overlook e-commerce sales, which have averaged a 15% growth rate over the last five years.

“That [growth rate] really kicked into high gear in 2010 when tablets hit the market,” Garrick says. “Apps got better, and we had more consumers embrace e-commerce. That disparity is not going away.”