background: Since the inception of the Medicare Part D benefit in 2006, Medicare stand-alone prescription drug plans (PDPs) have decreased in number by >50% across the country. Despite this, beneficiaries in 46 states still have at least 20 PDPs to choose from in 2018, each with a different formulary and cost-sharing structure. We sought to examine if, and how much, beneficiaries could save by switching to a different PDP. methods: Fourteen clinics were held in 10 cities across Northern/Central California during the fall of 2017. Trained student pharmacists utilized the Medicare Plan Finder Tool to assist beneficiaries with PDP selection based on the beneficiaries’ medication profile, preferred pharmacy(ies), and subsidy-status. Sociodemographic, plan information, medication(s), cost data of the beneficiaries’ current PDP and that of the lowest cost PDP in 2018, and interventional data were recorded. results: In total, 762 assisted beneficiaries had a PDP. We found that 571 (74.9%) beneficiaries had a potential out-of-pocket savings opportunity if they switched PDPs in the upcoming year. Aggregate potential cost savings resulting from Part D plan optimization totaled $936,522 (average of $1,229/beneficiary). Average potential out-of-pocket cost savings were significantly greater for subsidy recipients versus non-subsidy-recipients ($1,705 vs. $1,124, respectively). conclusion: Although the number of available PDPs has significantly decreased since Part D was first introduced, it still remains critical that beneficiaries reevaluate their Part D plan annually during the Medicare open enrollment period (the ‘annual checkup’). By doing so, beneficiaries can ensure they are receiving necessary medications at the lowest out-of-pocket cost.