The jump from 50 cents to 55 cents takes effect Jan. 27. It's the largest increase since 1991 when the price of a stamp went from 25 to 29 cents.
One patron outside the Fairmount post office said she planned to stock up on Forever stamps before the rate increase.
"I'm going to buy a whole roll of the Forever stamps now, because they never change their value. So I'll be a little ahead of the game if I buy a roll," she said.
While the cost of a 1 oz. letter is increasing to 55 cents, the cost of additional ounces is going down from 21 cents to 15 cents. That means the cost of a typical 2 oz. wedding invitation will decrease by a penny, from 71 cents to 70 cents.
The cost to mail a package is also going up. Postage for a small flat-rate box sent Priority Mail increases from $7.20 to $7.90, effective Jan. 27.
The Postal Service lost nearly $4 billion last year, citing a rise in pension and health care costs and a drop in mail volume.