Dive Brief:

• Retailers have begun their holiday promotions early this year as Black Friday continues to fizzle as retail’s all-important sales day. 

• But last year saw more shoppers saved their purchases till the week before Christmas, and CNBC’s Eric Chemi notes that their numbers could be even larger this year in light of research released by purchase-based data platform Cardlytics. 

• Last-minute shoppers were 36% of the total shoppers last year, giving retailers a 12% increase in physical store sales, and a 27% increase in online sales the week before Christmas. They also spent more, averaging $1,362 per person, almost $100 more than those shopping earlier, who spent an average $1,269 each.

Dive Insight:

The evolution of Black Friday includes a shift into Thanksgiving, the result of the Black Friday arms race. Right now, retailers are trotting out their Black Friday hours, and Black Friday, in light of its 11% drop in sales last year, seems a bit more subdued.

But Chemi notes that December sales may be taking over as a more important make-or-break time for retailers.

While Black Friday sales last year dropped nearly a full percentage point, sales in the week before Christmas rose a full two percentage points. Late shoppers represented the largest group of shoppers last year, and the Cardlytics data finds that will be larger this year.

"Retailers should run steady marketing campaigns starting before Thanksgiving and extending right up to Christmas," Cardlytics CMO Dani Cushion told CNBC. "A holiday marketing campaign that is too short leaves potential dollars on the table. Retailers should consider promoting shipping guarantees and simple gift guides to help last minute shoppers quickly and easily finish off their list."