The U.S. Postal Service has some new rates, including an increase in a first-class stamp to 55¢ (up from 50¢). However, the cost of additional ounces will decrease to 15¢ (down from 21¢), so the cost of sending heavier letters (e.g., event invitations with return envelopes) will decline. The cost for mailing a postcard is unchanged at 35¢. Find details about other rate changes from the USPS.