Is Medicare Prescription Drug Coverage Mandatory? 
Enrollment in a Medicare Prescription Drug Plan -LRB- Part D / PDP -RRB- is not mandatory . However , if you do not enroll in a Medicare approved Prescription Drug Plan , youll still need creditable prescription drug coverage to avoid a late enrollment penalty if you decide to enroll later on . To avoid the late enrollment penalty : Join a Medicare drug plan when you are first eligible and before your initial enrollment period is over . Dont allow 63 days or more in a row without a Medicare drug plan or other creditable prescription drug coverage . If you choose to delay getting a PDP plan , you are not penalized until you decide to enroll . This does come as a surprise to some people who choose to wait to buy a Medicare PDP plan after being on Medicare for some time . To calculate a late enrollment penalty fee , first determine how many months you went without creditable drug coverage . For example 43 months at a rate of $ 31.17 -LRB- 2013 -RRB- is 43 X .3117 = $ 13.40 . So , in addition to the monthly PDP premium , you would pay a $ 13.40 late enrollment penalty . You may have to pay this penalty for as long as you have a Medicare Prescription Drug Plan . In addition , the penalty rate may increase each year . This was a great question . I hope this answer was helpful . 