Even worse, premium costs will go up even more dramatically among some of the most popular plans in the country. According to the study, the 3.5 million Americans on the AARP MedicareRx Preferred Plan will see its premium rise from $602 to $749 on an annual basis, a climb of 21% from 2015's costs. Another AARP with almost 1.4 million participants will see even more dramatic increases of 26% to their premium costs.