Medicare Part D Plans: How Drug Coverage Works & What Changed for 2025

Medicare Part D adds prescription drug coverage to Medicare. You can get it through a stand-alone Part D plan (PDP) with Original Medicare (and/or Medigap) or via a Medicare Advantage plan with drug coverage (MAPD). Plans vary by premium, deductible, formulary (drug list), and pharmacy network.

In 2025, Part D was redesigned: there’s now a $2,000 annual cap on out-of-pocket Part D costs, and you may choose a monthly payment (smoothing) option for what you owe at the pharmacy.

What Part D Covers

• Outpatient prescription drugs on the plan’s formulary, organized by tiers (generic/brand/specialty).
• ACIP-recommended adult vaccines (e.g., shingles, RSV, Tdap, MMR) at $0—no copay and no deductible when covered by Part D.
• Insulin: Most Part D and Part B-covered insulin products are capped at $35 for a 1-month supply, with no deductible. (Three-month fills cap at $105.)

What Part D doesn’t cover: non-prescription drugs, most vitamins/supplements (unless plan-listed), and drugs specifically excluded by Medicare rules.

How Your Part D Costs Work (2025)

Part D has three stages in 2025:

• Deductible – You pay 100% until your plan’s deductible is met. (No plan may set a deductible higher than $590 in 2025; some plans have none.)
• Initial Coverage – You and the plan share costs (often % or copays) until your out-of-pocket spending on covered Part D drugs reaches $2,000.
• Catastrophic – After you hit $2,000 OOP, your copays for covered Part D drugs are $0 for the rest of the year.

New: Medicare Prescription Payment Plan (smoothing). You can opt to spread your out-of-pocket drug costs across monthly bills instead of paying the full amount at the pharmacy counter. All plans must offer it; participation is voluntary.

Eligibility & How to Get Part D

You’re eligible for Part D if you have Medicare and either:

• Enroll in a stand-alone Part D plan (typically used with Original Medicare ± Medigap), or
• Choose a Medicare Advantage plan with drug coverage (MAPD).

Enrollment windows:

• Initial Enrollment Period (IEP): 7-month window around your Part B start.
• Annual Enrollment Period (AEP): Oct 15 – Dec 7 (changes effective Jan 1).
• MA Open Enrollment (Jan 1 – Mar 31): If you move from MA → Original Medicare, you can also join a separate Part D plan.
• Special Enrollment Periods (SEPs): Certain life events (move, loss of coverage, Extra Help, 5-star plan availability, emergencies) allow changes.

Late Enrollment Penalty (LEP): If you go 63+ days without creditable drug coverage after first becoming eligible, you may owe a permanent monthly penalty added to your Part D premium. (Calculated from the national base premium—$36.78 in 2025—times uncovered months.)

Part D vs. Medigap & Medicare Advantage (Quick Guide)

• Original Medicare + Medigap + Part D: Any provider who accepts Medicare; add a stand-alone Part D for prescriptions.
• Medicare Advantage (MAPD): All-in-one plan with a drug formulary, networks, copays, and prior authorization rules.

Choose based on doctors, travel needs, medications, and risk tolerance.