FedEx (FDX) on Monday said it expects to move 317 million shipments during that period. It sees three significant volume spikes during those key weeks: Cyber Monday (the Monday following Thanksgiving weekend) and the first two Mondays in December, when FedEx predicts it will move more than double its average daily volume.

Many forecasters are forecasting a 3.5%-4% overall increase in total holiday sales, a deceleration from last year’s 5.2% growth. But the e-commerce segment remains a hot growth area as more shoppers move online for their holiday shopping needs. E-commerce sales are forecast to rise between 6% to 8% in 2015, hitting as much as $105 billion, the National Retail Federation has estimated.

The jump in online sales benefits shippers like FedEx and top rival United Parcel Service (UPS).

“The shift in consumer shopping patterns, fueled by the rise of e-commerce, continues to drive our volume,” said Frederick W. Smith, CEO of FedEx.

Forecasting for this critical season can be tricky for the shipping giants. In 2013, for example, UPS failed to deliver many packages in time for the holidays, a mishap that angered consumers and led to embarrassing headlines. But in 2014 it overcompensated, resulting in high costs when demand didn’t meet the company’s expectations.