The post office expects to deliver nearly 15 billion pieces of mail and 420 million packages during the holiday season.
The U.S. Postal Service said Wednesday that it expects letters to decline slightly while package deliveries between Thanksgiving and Dec. 31 will rise 12 percent over last year.
The calendar could make letter carriers' jobs tougher. Thanksgiving Day, the traditional kickoff to the peak season, is six days later this year, on Nov. 28.
"It'll be an interesting year this year. You'll have that volume crowded into four weeks instead of five," Postmaster General Patrick Donahoe said in an interview. "We'll be able to handle it."
The post office is adding 8,000 to 10,000 seasonal workers, Donahoe said.
The busiest mailing day is expected to be Monday, Dec. 16, and the busiest day for packages to be Thursday, Dec. 19.
Package deliveries are rising as more consumers shop online. United Parcel Service Co. expects daily volume during the holidays to increase 8 percent, and FedEx Corp. predicts a 13 percent rise during the busiest week in early December.
The Postal Service is looking to increase sales online, which enable customers print shipping labels and buy postage at home. It's also selling a special holiday stamp featuring gingerbread houses, but there might be fewer people using it.
"Greeting cards are fairly stable," Donahoe said. "You might lose a (percentage) point or two (compared with last year), but it's not a real big change."