Medicare Part D Plans

5 things to know about Medicare Part D drug plans:

  1. Medicare Part D plans provide prescription drug coverage.
  2. About 23.2 million people were enrolled in stand-alone Medicare Part D plans in 2015, according to the Kaiser Family Foundation (KFF).
  3. Part D plans may have different benefits, formularies, tiers, coverage rules, and pharmacy networks.
  4. Part D costs can include plan premiums, late enrollment penalties, and "donut hole" costs.
  5. You should review Part D plan costs, coverage rules, and star ratings before enrolling in a plan.

Medicare Part D provides prescription drug coverage for Medicare enrollees. Part D plans are offered by private insurers, not the federal government. It is optional coverage that works with many other forms of insurance, including Original Medicare, Medicaid, employer health plans, and, in some cases, Medicare Advantage plans.

In 2015, approximately 23.2 million people had prescription drug coverage through a Medicare Part D plan, according to the KFF.

Each Part D prescription drug plan may have varying benefits, costs, and rules.

Enrollment and eligibility

You must be enrolled in Medicare Part A and/or Part B before you can enroll in a Medicare Part D prescription drug plan.

You must wait for an enrollment period to sign up for, make changes to, or leave a Medicare Part D plan.

More info: Part D enrollment and eligibility - How to enroll


Part D plans have different formularies, tiers, coverage rules, and pharmacy networks.

A Part D plan formulary (drug list) outlines which prescription drugs are covered. Plans may place prescription drugs into tiers, which have different costs.

Coverage rules such as quantity limits, prior authorization, and step therapy may limit how and when you receive your prescription drugs.

Part D plans also may have pharmacy networks, which may impact the cost of your prescription drugs.

More info: Part D benefits

Part D costs

Medicare Part D prescription drug plans are not free. If you have a Part D plan, you may have to pay premiums, "donut hole" drug costs, and other out-of-pocket costs like deductibles.

More info: Part D costs - Premiums, deductibles, and the donut hole

Comparing plans

There are many Part D plans to choose from. Most regions have about 30 different plans available, according to the KFF.

Before you choose a plan to enroll in, you should review its benefits, costs, and star ratings.

Our online plan comparison tool can help you easily evaluate all of these factors for available plans in your area offered through this website.

More info: Comparing Part D plans