It's a surprisingly complicated little science, so we're glad to share the wisdom of DealNews.com, which combs through retailer sales information from previous years to offer guidance and predictions for this year.
First off, here's their list of what to buy now: Brand name HDTVs (because new models are unveiled at a January electronics sale); fitness gear (stores such as REI had sales of 50%, 60%, and 50% off respectively last year); home furniture (new models released in February), especially mattresses; consumer electronics; clothing and accessories; and, of course, Christmas decor.
BusinessInsider offers this list of 30 after-Christmas deals, many of which will last for several days.
Here's a sampling:
JC Penney: 15 to 25 percent off; $10 off in-store coupon of $25 or more purchase.
Kohl's: Spend $100 or more and save 20%, 60 to 80 percent off certain items.
Macy's: 15% off sale and clearance apparel, fine and fashion jewelry; 10% off sale and clearance watches, coats, suits, dresses, intimates, select shoes and home items.
Target: Up to 60 percent off; discounted video game consoles.
Nordstrom: Up to 50% off sale items; Earn double points through Friday.
Old Navy: Up to 75% off in store or up to 60% off online until Dec. 31
Best Buy: Open until 11 p.m. tonight.
Toys R Us: Buy one, get one 40% off select video games; Buy one, get one 40% off select movies.