7.1 Part D Overview & Eligibility

Why Part D Overview & Eligibility Matters on the AHIP Exam

Module 3 (Part D Prescription Drug Plans) carries a 15% weight on the AHIP Medicare final — the lightest of the five modules, but do not mistake "lightest" for "skippable." Every agent selling a Medicare Advantage Prescription Drug (MA-PD) plan or a standalone Prescription Drug Plan (PDP) is legally required to get the mechanics of Part D right, because a client who cannot afford their insulin or cardiac medication because you enrolled them in the wrong plan type is both a compliance problem and a real harm. The AHIP exam tests whether you know who can enroll, how they get coverage, and when enrollment happens — and Module 3 questions frequently combine with Module 1 (enrollment periods) and Module 4 (marketing rules), so a shaky foundation here costs you points in three modules, not one.

What Medicare Part D Is

Medicare Part D is the voluntary outpatient prescription drug benefit created by the Medicare Prescription Drug, Improvement, and Modernization Act of 2003 (MMA), effective January 1, 2006. Unlike Part A and Part B, which the federal government administers directly, Part D benefits are delivered exclusively through private insurance companies under contract with the Centers for Medicare & Medicaid Services (CMS). This is a foundational exam point: there is no "Original Medicare Part D" — every beneficiary who wants drug coverage must enroll in a private plan.

As of February 2026, 56.1 million Medicare beneficiaries are enrolled in Part D coverage, according to KFF analysis of CMS enrollment data. Of that group:

Two Ways to Get Part D Coverage

A beneficiary gets Part D drug coverage one of two ways, and the AHIP exam expects you to know the rule that connects them:

1. Standalone PDP — paired with Original Medicare (Parts A and B), or with a Medicare Advantage plan that does not include drug coverage (an MA Medical Savings Account plan, or certain Private Fee-for-Service plans without embedded Part D).
2. MA-PD — drug coverage bundled directly into a Medicare Advantage (Part C) plan, such as an HMO-PD or PPO-PD.

The one-plan rule: a beneficiary generally cannot be enrolled in both a standalone PDP and an MA-PD at the same time. If someone already in an MA-PD plan enrolls in a standalone PDP, CMS will treat that as an implicit request to disenroll from the MA-PD and return to Original Medicare — an outcome that can blow up a client's coverage if an agent does not explain it clearly. The recognized exception is Medicare Medical Savings Account (MSA) plans and some Cost Plans, which are legally barred from including Part D benefits, so enrollees in those plans are expected to pair them with a standalone PDP.

Eligibility Requirements

To enroll in Part D, a person must:

• Be entitled to Medicare Part A or enrolled in Medicare Part B (only one of the two is required, not both), and
• Live in the service area of the plan they want to join.

There is no income test, no health screening, and no medical underwriting for Part D enrollment itself (though premiums can carry an income-related surcharge — the Income-Related Monthly Adjustment Amount, or IRMAA — for higher earners, similar to Part B).

Enrollment Timing (Cross-Reference)

Part D follows the same enrollment period structure taught in Chapter 3: the Initial Enrollment Period (IEP), the Annual Enrollment Period (AEP, October 15 – December 7), and various Special Enrollment Periods (SEPs). One detail specific to Part D: someone who delays enrollling without creditable coverage (drug coverage at least as good as standard Part D, such as many employer plans) can face a Late Enrollment Penalty (LEP) that accrues for every month of the gap — covered in full in Section 8.2. Do not confuse Part D's LEP mechanics with the MA OEP (Medicare Advantage Open Enrollment Period, January 1 – March 31), which allows only one MA-to-MA or MA-to-Original-Medicare switch and does not independently open standalone PDP enrollment for someone who stayed in Original Medicare all along.

Auto-Enrollment and Facilitated Enrollment

CMS does not leave the most vulnerable beneficiaries without drug coverage by default:

• Dual eligibles (people enrolled in both Medicare and Medicaid) who do not actively choose a PDP are auto-enrolled into a randomly assigned benchmark plan (a plan with premiums at or below the regional low-income subsidy benchmark) so they are never without coverage.
• Other beneficiaries who qualify for the Low-Income Subsidy (LIS/Extra Help) but have not selected a plan receive facilitated enrollment, a similar CMS-driven assignment process.

Agents should know that these beneficiaries retain the right to switch out of their assigned plan at any time using a Special Enrollment Period — auto-enrollment is a safety net, not a lock-in.

Common Exam Traps

• Thinking Part D is administered by CMS directly — it is always a private plan.
• Forgetting that MSA plans require a standalone PDP because they are barred from bundling drug coverage.
• Assuming both Part A and Part B are required for Part D eligibility — only one is required.
• Confusing "creditable coverage" (employer coverage that lets you delay Part D penalty-free) with "no coverage" (which starts the LEP clock running).

Quick Scenario

A client turning 65 has excellent drug coverage through a spouse's employer plan and wants to delay Part D. Before recommending that, an agent must confirm in writing that the employer plan is documented as creditable coverage — otherwise the client accrues an LEP the moment they do eventually enroll, calculated from the end of their IEP.