How Medicare Part D works: coverage, costs, and enrollment in 2026

If you are on Medicare or about to enroll, prescription drug costs are probably on your mind. Medicare Part D is the part of Medicare that covers outpatient prescriptions, but it works differently from Parts A and B. It is optional, it is run by private insurance companies, and the details vary from plan to plan. Missing the enrollment window can also cost you a permanent penalty.

This guide explains how Part D works in 2026, what it covers, what it costs at each stage, how formularies and plan rules affect your access to medications, and what Triangle residents can do to compare plans before making a decision.

What is Medicare Part D, and who needs it?

Medicare Part D is prescription drug coverage you get through a private insurance plan approved by Medicare. It is not run by the government directly. You can get Part D two ways:

• Standalone Part D plan (PDP) that works alongside Original Medicare (Parts A and B), with or without a Medigap policy.
• Medicare Advantage plan with drug coverage (MA-PD) , where hospital, medical, and drug coverage are bundled into one plan.

You are not required to enroll in Part D. But if you skip it and do not have what Medicare calls "creditable coverage" (drug coverage at least as good as Part D), you may face a late enrollment penalty down the road.

Most people become eligible for Part D when they first become eligible for Medicare, usually at age 65. If you are still working and have employer drug coverage, you may be able to delay enrolling without a penalty, as long as that coverage qualifies as creditable. Your employer or union plan sends you a notice each year telling you whether it does.

How Part D coverage and formularies work

Part D covers outpatient prescription drugs that you fill at a pharmacy or through mail order. It does not cover drugs you receive during a hospital stay or at a doctor's office for injection (those fall under Part A or Part B instead).

Each Part D plan has its own formulary , which is a list of drugs the plan covers. Formularies are organized into tiers, and each tier has a different cost-sharing amount. A drug on a preferred generic tier might have a low copay, while a brand-name drug on a higher tier could cost you significantly more out of pocket.

Protected classes

Medicare requires Part D plans to cover most drugs in six protected classes:

• Antidepressants
• Antipsychotics
• Anticonvulsants
• Antiretrovirals (for HIV)
• Antineoplastics (cancer drugs)
• Immunosuppressants (for transplant patients)

Plans have some flexibility, but they generally cannot exclude these categories outright. Outside these classes, plans decide which drugs to include and at what tier, so two plans in the same ZIP code can look very different.

Plan rules that can affect access

Beyond the formulary itself, a plan may apply:

• Prior authorization : Your doctor must get approval from the plan before certain drugs are covered.
• Step therapy : You may need to try a less expensive drug first before the plan covers a pricier one.
• Quantity limits : The plan may limit how much of a drug you can get per fill.

If your plan denies a drug or imposes a restriction, you can ask your doctor to request an exception. Plans have a process for that, though Medicare sets timelines for how quickly they must respond.

What Part D does not cover

Part D does not pay for over-the-counter medications, most drugs for weight loss or weight gain, cosmetic or hair-growth drugs, fertility treatments, or drugs for erectile dysfunction. There are narrow exceptions in some cases, but these categories are generally excluded by Medicare rules. Many adult vaccines, on the other hand, are covered at $0 copay under Part D, with no deductible applied.

Standard Part D costs and the out-of-pocket cap

Part D costs in 2026 move through a few stages. The exact amounts you pay depend on your plan, but Medicare sets the structural limits that all plans must follow. These 2026 figures come from current CMS guidance and should be verified each year on Medicare.gov as amounts can adjust with inflation and policy updates.

Stage 1: Annual deductible

In 2026, the maximum Part D deductible is $615 . Some plans set a lower deductible, and a few have no deductible at all. You pay the full cost of your drugs (up to the deductible amount) before the plan's coverage kicks in. As of 2026, the deductible limit comes from CMS guidance on Part D redesign parameters (CMS.gov, April 2025).

Stage 2: Initial coverage

After you meet the deductible, you and the plan share costs. Under the redesigned Part D structure, you typically pay about 25% coinsurance on covered drugs during this phase. Your plan pays the rest. This continues until your total out-of-pocket costs for covered drugs reach $2,100 in 2026 (the "true out-of-pocket" or TrOOP threshold). That $2,100 includes what you paid during the deductible stage and your share of costs in initial coverage, but it does not include your monthly premium.

Stage 3: Catastrophic coverage

Once your out-of-pocket spending hits $2,100, catastrophic coverage begins. For the rest of the year, you pay $0 for covered Part D drugs. There is no donut hole. People sometimes ask about the old coverage gap, but that was eliminated starting in 2025 as part of the Inflation Reduction Act redesign. The current structure is considerably simpler: deductible, initial coverage, and then full coverage after the cap.

For someone with expensive prescriptions who hits the $2,100 mark early in the year, this means no further drug costs for covered medications for the rest of the calendar year. For someone with one or two inexpensive generics, the cap may never come into play, and monthly costs stay low.

Enrollment periods and late penalties

Timing matters with Part D. Here are the main windows:

Initial Enrollment Period (IEP)

This is the seven-month window around your 65th birthday (three months before, the birthday month, and three months after). Most people sign up for Part D during this period if they do not have creditable drug coverage through an employer.

Annual Enrollment Period (AEP)

Each year from October 15 through December 7 , you can join, switch, or drop a Part D plan. Changes take effect January 1.

Special Enrollment Periods (SEPs)

Certain life events like moving to a new ZIP code, losing creditable coverage, or qualifying for Extra Help can open a special window. These are situation-specific, so it is worth checking with Medicare or a counselor if something changes.

The late enrollment penalty

This is the part that catches people off guard. If you go 63 or more consecutive days without creditable drug coverage after your IEP ends, Medicare adds a penalty to your monthly Part D premium. The penalty is 1% of the national base beneficiary premium for each month you were uncovered . In 2026, that base premium is $38.99 , according to Medicare.gov.

Here is what that looks like in practice. Say someone delays enrollment for 43 months without creditable coverage. Their penalty would be 43% of $38.99, which is roughly $16.80 added to their monthly premium every month, for as long as they have Part D. That penalty does not go away. It is permanent.

A few things to know: the penalty amount can change each year because the base premium can change. And if you have continuous creditable coverage through an employer or other source, the penalty clock does not start.

How to compare and verify Part D plans

Part D plans are not one-size-fits-all. Costs, pharmacy networks, and covered drugs all vary by plan and ZIP code. Two things can help you compare:

Medicare Plan Finder (Medicare.gov) : You can enter your medications, dosages, preferred pharmacies, and ZIP code to see estimated annual costs for plans in your area. The tool will show deductibles, copays, plan premiums, and whether your drugs are on the formulary. For someone living in Cary (27511), Raleigh, Durham, or any Triangle ZIP code, this is the most direct way to see what is actually available near you.

Your drug list : Before comparing plans, write down every prescription you take, including dose, frequency, and whether it is generic or brand-name. This lets you plug accurate information into Plan Finder and gives a counselor the details they need to help you compare.

What Triangle residents should know about NC SHIIP

If the plan comparison process feels overwhelming, North Carolina has a free resource that can help. NC SHIIP (the Seniors' Health Insurance Information Program) is run by the North Carolina Department of Insurance and provides free, unbiased counseling on Medicare topics, including Part D.

SHIIP has trained volunteers in all 100 counties in North Carolina, including in Wake County and the Cary area. They can walk you through Plan Finder, explain how your prescriptions would be covered under different plans, and help you understand whether your current coverage counts as creditable. This is not a sales service. The counselors do not sell insurance or represent any carrier.

You can reach SHIIP by phone at 1-855-408-1212 or through the NC Department of Insurance website at ncdoi.gov to find a location near you. Many local senior centers in the Triangle area host SHIIP counselors, particularly during Medicare Open Enrollment in the fall.

Questions worth asking before you enroll

Whether you are working with SHIIP, a licensed agent, or going through Plan Finder on your own, here are some things worth checking:

• Are all of my current prescriptions on the plan's formulary, and what tier are they on?
• Do any of my drugs require prior authorization or step therapy?
• Is my pharmacy in the plan's preferred network? Mail order may be a different cost than a local pharmacy.
• What is the total estimated cost for the year, including premium, deductible, and expected copays?
• Does this plan bundle drug coverage, or do I need a separate Part D plan alongside Original Medicare?

The right plan for you depends on the specific prescriptions you take, the pharmacies you use, your income, and whether you are also enrolled in Original Medicare or Medicare Advantage. That is not something any article can decide for you. But knowing the mechanics means you can ask better questions and spot differences that matter.

For a broader overview of Medicare options and related topics, visit the Medicare enrollment periods and late penalties guide of this site. If you have a specific question about Part D or another Medicare topic, you can also ask a question and we will do our best to point you in the right direction.