Retailers are looking to a final burst of shopping to close out the year on a high note, as customers flock to post-Christmas sales, exchange presents and use up their gift cards.

It is being dubbed "Mega Monday," and it reportedly is gearing up to be the third biggest shopping day of the year, behind Black Friday and Christmas Eve. Stores across the country opened early to accommodate the extra business.

"There's great deals and there's a lot of people out shopping. It's been a spectacular holiday shopping season," retail analyst Kit Yarrow told CBS News. "The day after Christmas is now considered to be up there with 'Black Friday' as one of the hugest shopping days of the year."

Stores are expected to ring up $469.1 billion during the holiday season, which runs November through December. The final week before Christmas can account for up to 20 percent of those sales.

Retailers tempered their expectations heading into the season because they worried that Americans weren't ready to spend in the weak economy.

But sales have been brisk during the two-month period, rising 2.5 percent from the start of the season on Nov. 1 through last Saturday, according to research firm ShopperTrak, which did not give a dollar figure. As a result, ShopperTrak upgraded its sales growth forecast to 3.7 percent from its 3 percent estimate heading into the season.

The Associated Press contributed to this report.