If you do not take Part D when eligible and do not have creditable coverage through a group, Senior Care, or the Veterans Administration, you will be penalized when you join a Medicare Part D plan. The penalty is 1% per month for every month you don’t have creditable coverage.  It is based on the national average premium of drug plans, which changes every year. This not a one- time penalty, it is a lifelong penalty that is accessed every month you are on a Part D plan.