It'll cost you an extra 10% to hedge your bet on the future cost of mailing a first-class letter.

The United States Postal Service announced on Sunday that the price of its first-class "forever" stamp went up to 55 cents from 50 cents, the largest single price jump in the Postal Service's history, according to the Associated Press.

Part of the reason: a $3.9 billion loss in 2018, driven in part by a drop in first-class mail volume, which decreased by about 2.1 billion pieces, according to the USPS.

"Reforms are necessary to enable the Postal Service to further reduce costs, grow revenue, compete more effectively, function with greater flexibility to adapt to a dynamic marketplace and to prudently invest in our future," Postmaster General and CEO Megan Brennan said in a statement.

"The Postal Service will remain focused on aggressively managing our business. We will take all appropriate actions within our control to ensure that we can continue to fulfill our primary mission to provide prompt, reliable and efficient service to American businesses and consumers in all communities in our country."

While first-class mail delivery has fallen, the Postal Service's package business has grown, according to the USPS. Last year saw an increase of almost half a billion additional packages compared to the year before, the USPS said.

The following U.S. Postal Service 2019 price increases take effect Sunday:

  • First-class Forever stamps will increase from 50 cents to 55 cents
  • Small flat-rate box from $7.20 to $7.90
  • Medium flat-rate box from $13.65 to $14.35
  • Large flat-rate box from $18.90 to $19.95
  • Regular flat-rate envelope from $6.70 to $7.35
  • Large flat-rate envelope from $7 to $7.65
  • Padded flat-rate envelope from $7.25 to $8.