Do I need Part D if I don't take any medications?

It's a good idea to enroll when first eligible even if you take no prescriptions today. If you go 63 days or more without "creditable" drug coverage and later sign up, you'll owe a permanent late-enrollment penalty added to your monthly Part D premium for as long as you have Medicare. The penalty is 1% of the national base beneficiary premium for each month you went without, and it adds up.

A formulary is the list of prescription drugs a Part D plan covers, organized into tiers (generic, preferred brand, non-preferred brand, specialty). The same drug can be on different tiers in different plans, which changes your copay or coinsurance significantly. Before enrolling, always check that your specific medications are on the plan's formulary at a tier you can afford.

Are Part D and Medicare Advantage drug coverage the same?

The benefits design is similar (formularies, tiers, deductibles), but they're packaged differently. A stand-alone Part D plan pairs with Original Medicare or a Medigap policy. A Medicare Advantage Prescription Drug (MAPD) plan bundles your medical and drug coverage into one plan. You typically choose one or the other, you can't have a stand-alone Part D plan and a Medicare Advantage plan with drug coverage at the same time.

What is the "donut hole"?

The coverage gap (often called the "donut hole") was a phase of Part D where you paid a higher share of drug costs after reaching an initial coverage limit and before reaching catastrophic coverage. The Inflation Reduction Act made significant changes to the Part D benefit structure beginning in 2024 and 2025, including a $2,000 annual out-of-pocket cap. Check Medicare.gov for the current year's structure as it continues to evolve.

How do I know which Part D plan is best for my medications?

The Medicare Plan Finder at Medicare.gov lets you enter your specific medications and pharmacies and shows estimated annual costs for each plan available in your ZIP code. A licensed agent can also run this comparison for you and explain the trade-offs.

Medicare Part D Prescription Drug Plans Explained

What is Medicare Part D?

Part D is the part of Medicare that covers retail prescription drugs. It's offered by private insurance companies that contract with Medicare. You get Part D coverage in one of two ways:

A stand-alone Part D plan, bought separately and paired with Original Medicare (and usually a Medigap policy)
A Medicare Advantage Prescription Drug (MAPD) plan , drug coverage bundled into a Medicare Advantage plan

You generally can't have both at once. If you enroll in a MAPD plan while you have a stand-alone Part D plan, you may be automatically disenrolled from one of them.

How Part D plans are structured

Every Part D plan has a few moving parts:

Monthly premium, what you pay every month just to have the plan
Deductible, what you pay out of pocket before the plan starts covering drugs (some plans have $0 deductible)
Copays/coinsurance, what you pay for each prescription after meeting the deductible, varies by drug tier
Formulary, the list of drugs the plan covers, organized into tiers
Pharmacy network, which pharmacies offer the plan's preferred (lower-copay) pricing
Annual out-of-pocket cap, Part D now has a maximum yearly out-of-pocket cost for prescriptions (introduced by the Inflation Reduction Act)

Formularies and tiers

A formulary is the master list of drugs a plan covers. Plans typically organize covered drugs into 4-6 tiers:

Tier 1: Preferred generics, lowest copay
Tier 2: Generic drugs
Tier 3: Preferred brand drugs
Tier 4: Non-preferred drugs (often a percentage rather than a flat copay)
Tier 5: Specialty drugs, highest cost-sharing

The same medication can land in different tiers across plans, which can mean a difference of hundreds or thousands of dollars a year. Always check the formulary tier for your specific medications before enrolling.

The Part D late-enrollment penalty

One of the most important things to know about Part D: delaying enrollment costs you for life.

If you go 63 days or more without "creditable" prescription drug coverage (defined as coverage that's at least as good as standard Part D) after becoming eligible for Part D, you'll owe a late-enrollment penalty when you eventually enroll. The penalty is 1% of the national base beneficiary premium for each month you went without, added to your monthly Part D premium for as long as you have Part D.

Examples of creditable coverage that pauses the penalty clock: many employer or union plans, the VA prescription benefit, and TRICARE. Your plan should send you a notice each year stating whether your coverage is creditable.

Pharmacy networks matter too

Most Part D plans have preferred pharmacies where copays are lower, and standard pharmacies where they're higher. Mail-order pharmacies are often the lowest-cost option for maintenance medications.

Before enrolling, check whether your usual pharmacy is in the plan's preferred network. Switching to a preferred or mail-order pharmacy can dramatically lower your annual costs.

When you can enroll in or change Part D

Initial Enrollment Period, the 7-month window around your 65th birthday
Annual Enrollment Period (AEP), October 15 to December 7 each year, for coverage starting January 1
Special Enrollment Periods, triggered by qualifying events like losing employer coverage, moving, or qualifying for Extra Help

For more on enrollment timing, see our Medicare enrollment periods guide.

Medicare Part D prescription coverage, explained.