The United States Postal Service is set to raise the price on postage stamps Sunday, Jan. 27, that will impact the price of not only stamps but also flat-rate boxes and envelopes sold by the agency and other shipping and mailing services. Postage for a one-ounce letter will increase from 50 cents to 55 cents, though the postage for additional ounces will decrease from 21 cents to 15 cents. Discounted metered letter postage will increase from 47 cents to 50 cents.