Black Friday: a Two-Day Affair

The traditional kickoff to the holiday shopping season has become a two-day affair, with more stores opening before people put down their turkey legs on Thanksgiving.

There's good reason for the creep; businesses know shoppers will only spend so much, and they want the first crack at grabbing those holiday dollars. Still, millions of Americans are expected to head out in search of steep discounts today, the traditional start to the annual shopping binge.

The National Retail Federation expects holiday sales to grow 4.1 percent to $616.9 billion - the highest increase since 2011.

The holiday shopping season is a make-or-break time for many retailers, which can get as much as 20 percent of their annual sales during the time. Already, retailers have resorted to steep discounting to lure shoppers.

As far as getting the best bargain, it may already be too late. Analysis of sales data and store circulars by two research firms says the hottest deals of the season may have been on Thanksgiving.