Most of the Social Security cost-of-living adjustment will be used to pay for higher Medicare Part B premiums. The standard Medicare Part B monthly premium will be $134 in 2018, the same amount as in 2017. But many retirees who have been paying less than the standard rate for the past several years will see a jump in their premiums. Here’s a look at how much you can expect to pay for Medicare Part B premiums in 2018.