NEW YORK (AP) -- Call it the pregame show for Santa and his elves. Monday is expected to be the busiest day in FedEx history, with nearly 16 million packages moving on its conveyer belts, trucks and planes. That's up 13 percent from 14.2 million on the busiest day last year, and double what the company handles on a normal day. That jump in shipments bodes well for the nation's retailers, online stores and larger rival UPS, which has its single busiest day next week. About half of the increase is from the company's SmartPost partnership with the U.S. Postal Service. SmartPost moves lighter, cheaper packages through FedEx that are then delivered by a postal worker. A growing number of online and catalog purchases is driving growth in that unit and across the company. Online holiday spending since Nov. 1 is up 12 percent over last year to nearly $22 billion, according to research company comScore. Last Monday and Wednesday ranked in the top five days for online spending ever, comScore said. Online orders are likely to spike again this Friday, which many merchants are promoting as "Free Shipping Day." Online spending increases come with modestly brighter prospects for holiday spending in general. Retail experts predict overall spending will increase by 2 to 4 percent over last year. Severe weather, including a weekend blizzard in the Midwest, is not hindering deliveries significantly on FedEx's busiest day, spokeswoman Deborah Willig said. There are scattered road closures and dangerous driving conditions in parts of the Midwest. Snow is still falling around the Great Lakes. Although this week is the busiest for both UPS and FedEx, you still have time to send packages to be under the tree by Christmas. The last day for guaranteed FedEx ground service delivery is Friday. Procrastinators can choose more expensive options like FedEx two-day shipping until Tuesday, Dec. 21, or overnight service through Dec. 23. UPS expects its busiest day closer to Christmas, on Dec. 22 when it will move about 24 million packages. That's 60 percent more than a normal day. The Atlanta-based company will accept packages for Christmas delivery through Dec. 23. FedEx's busiest day is the high water mark of a holiday season in which it expects to move 223.3 million shipments worldwide. That's 86 packages delivered every second from Thanksgiving Day to Christmas Eve. UPS will deliver almost double that - 430 million packages - between the two holidays. This week FedEx will move more than 63 million packages compared with 57.5 million last year. Wondering what's in Santa's sacks? FedEx says it's mostly books from Internet retailers like Amazon.com, clothing purchases, personal electronics such as iPads and smart phones, as well as luxury goods. High-tech imports from Asia, including iPhones and computers, have driven growth for both FedEx and UPS this year, as businesses invest in hardware upgrades and consumers stock up on the latest gadgets. FedEx relies on its 285,000 employees working overtime to handle the holiday rush. UPS hired 50,000 part-time workers to help sort and deliver the packages to their destinations - about the same number it hired last year. Industry analysts and economists track FedEx and UPS shipping performance for signs of consumer spending trends and the health of the broader economy, because both shippers handle a wide variety of goods shipped between manufacturers and consumers.