What Is Medicare Part D? A 2026 Complete Guide

Medicare Part D is an optional federal program that helps Medicare beneficiaries cover prescription drug costs. It covers most outpatient medications, from common generics to specialty drugs. Part D plans are offered by private insurance companies and approved by Medicare. 

You can get Part D as a stand-alone plan or bundled with a Medicare Advantage plan. This guide explains what Part D covers, who is eligible, and how to enroll. For a full breakdown of 2026 costs, including monthly premiums, visit our Medicare Part D costs guide.

What is Medicare Part D?

Medicare Part D plans cover most outpatient prescription medications. These plans are offered by private insurance companies and regulated by the Centers for Medicare & Medicaid Services (CMS).

Medicare Part D Eligibility

Most people aged 65 or older are eligible for Medicare prescription drug plans. People under 65 with certain disabilities may also qualify. How you get Part D depends on the type of Medicare coverage you have.

1. Part D With Original Medicare (Parts A and B)

If you’re enrolled in Original Medicare Part A and/or Medicare Part B, you can sign up for a stand-alone Medicare Part D prescription drug plan. Many people also add a Medicare Supplement plan to help cover out-of-pocket costs like deductibles and coinsurance.

2. Part D Bundled With a Medicare Advantage Plan

When enrolled in Medicare Part C (Medicare Advantage), your plan often includes Part D drug coverage. These are called Medicare Advantage Prescription Drug (MAPD) plans. Note that if you have a Medicare Advantage plan, you generally cannot also enroll in a stand-alone Part D plan.

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Medicare Part D Coverage

Part D plans must cover a wide range of prescription drugs. According to Medicare.gov, every plan must include at least two medications from most drug categories, and must cover all drugs in certain protected classes, including:

• HIV/AIDS treatments
• Antidepressants
• Antipsychotic medications
• Anticonvulsive medications for seizure disorders
• Immunosuppressant drugs
• Anticancer drugs (unless already covered under Part B)

Part D plans also cover most vaccines not already covered by Medicare Part B.

Part D Drug Plan Formulary

Every plan has a list of covered medications called a “formulary.” Plans don’t cover every drug, so always check the formulary before enrolling. If your medication isn’t on the list, you may request an exception, pay out-of-pocket, or file an appeal.

Formularies can change during the year, for example, when new drugs are approved or when Medicare issues guidance. Review your plan’s coverage every year during the Annual Enrollment Period.

Agent tip:

Plan premiums and plan formularies can change every year. A Part D plan that worked well for you may no longer cover your medications or may cost more in 2026. Always review your Part D coverage during the Annual Enrollment Period (October 15 – December 7) to make sure your plan still fits your health and budget needs.

Drug Tiers and What They Mean for Your Costs

Each formulary organizes drugs into “tiers.” Lower tiers cost less. Here is a common example, though tiers vary by plan:

• Tier 1 – Preferred Generic: Lowest copay. Most generic drugs.
• Tier 2 – Generic: Medium copay. Generic medications.
• Tier 3 – Preferred Brand: Higher copay. Preferred brand-name drugs.
• Tier 4 – Brand: Higher copay. Non-preferred brand-name drugs.
• Tier 5 – Specialty Drugs: Usually a coinsurance. Very high-cost medications.

When possible, ask your doctor about generic options. According to the FDA, generics use the same active ingredients as brand-name drugs and are equal in dosage, safety, and strength — often at a fraction of the cost.

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Medicare Part D Enrollment Periods

Signing up at the right time is important. If you miss your enrollment window, you may face a late enrollment penalty. This penalty is added to your monthly Part D premium and never goes away as long as you have Part D coverage. 

According to Medicare.gov, the penalty is calculated by multiplying 1% of the national base beneficiary premium by the number of full months you went without creditable drug coverage. The longer you wait, the higher your penalty will be. That is why it is important to enroll in Part D as soon as you are eligible.

Initial Enrollment Period (IEP)

Your Initial Enrollment Period is the best time to sign up. It’s a seven-month window, starting three months before your 65th birthday month, including your birthday month, and ending three months after. You can enroll in a stand-alone Part D plan or a Medicare Advantage Prescription Drug plan during this time.

Special Enrollment Period (SEP)

A Special Enrollment Period allows you to enroll outside of your Initial Enrollment Period if you experience a qualifying life event, such as retiring, losing employer drug coverage, or moving out of your plan’s service area. Most SEPs last 60 days.

If you lose creditable employer drug coverage and don’t enroll during your SEP, you may face a late enrollment penalty when you do sign up. Learn more about how the penalty affects your costs in our Medicare Part D costs guide.

Annual Enrollment Period (AEP) 

Each year from October 15 through December 7, during the Annual Enrollment Period (also called the Open Enrollment Period), you can join, drop, or switch your Part D or Medicare Advantage Prescription Drug plan. This is your once-a-year chance to make sure your coverage still fits your needs. Plans can change every year, including which drugs they cover, what tier your medications fall under, and how much you pay. 

Your health needs may have changed, too. Maybe you were prescribed a new medication, or your current plan no longer covers a drug you take regularly. Reviewing your plan each year during this window can help you avoid unexpected costs and ensure you have the right coverage heading into the new year.

How to Apply for Medicare Part D

To enroll, find a plan that covers your medications at a cost you can afford. A local licensed Connie Health insurance agent can help you compare Part D and Medicare Advantage Prescription Drug plans in your area, check your formulary, and estimate your costs.

Bottom Line

Medicare Part D helps cover the cost of prescription drugs for people with Medicare. It covers most outpatient prescription drugs, from common generics to specialty and brand-name drugs. You may be eligible if you are enrolled in Medicare Part A or Part B. 

You can get Part D as a stand-alone plan or as part of a Medicare Advantage plan. Signing up on time is important to avoid a late enrollment penalty that never goes away. Review your plan each year to make sure your coverage still fits your health and budget needs. 

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Frequently Asked Questions

Can I have Medicare Part D and Medicaid at the same time?

Yes. If you have both Medicare and Medicaid, you are considered “dual eligible.” You may automatically qualify for Extra Help, a program that reduces your Part D premiums, deductibles, and copays. A licensed agent can help you understand your options.

What happens to my Part D coverage if I move to a new state?

Most Part D plans have a service area. If you move out of your plan’s coverage area, you will qualify for a Special Enrollment Period to switch to a new plan. It is important to act quickly to avoid a gap in drug coverage.

Can I switch Part D plans outside of the Annual Enrollment Period?

In most cases, no. You can only switch plans during the Annual Enrollment Period or if you qualify for a Special Enrollment Period due to a life event such as moving, losing other coverage, or qualifying for Extra Help.

Does Medicare Part D cover medications given in a doctor's office?

Not always. Some medications administered in a doctor’s office or outpatient setting are covered under Medicare Part B instead of Part D. Check with your doctor or plan to confirm which part of Medicare covers your specific medication.

What is the difference between a Part D plan and a Medicare Advantage Prescription Drug plan?

A stand-alone Part D plan adds drug coverage to Original Medicare. A Medicare Advantage Prescription Drug (MAPD) plan bundles hospital, medical, and drug coverage into one plan. Both cover prescription drugs but work differently depending on your other Medicare coverage.