The average basic Medicare Part D premium for prescription drug plans is projected to decline, CMS announced. The announcement outlined a trend that’s extended over the past three years. Part D premiums decreased by 13.5% since 2016, saving beneficiaries around $1.9 billion. The actual average Part D premium in 2017 was $34.70. CMS projects that for 2020 the average Part D premium will decline to $30, a decline of around 13.5%.