One of those subsidies, the Part D Premium Stabilization Demonstration, reduced enrollee premiums on “standalone” Part D plans, typically purchased by those on Traditional Medicare. Though nominally voluntary, the demonstration amounted to a national policy covering 99 percent of enrollees in standalone plans. As the figure below illustrates, the inflation-adjusted average premiums for standalone Part D plans are far below historical norms. In fact, enrollees only bear roughly 13% of the cost of Part D plans overall—down from nearly 26% historically. The IRA increased program costs far more than anticipated and policymakers have leaned on taxpayers to absorb those expenditures.