Medicare Part D: Prescription Drug Coverage Explained

Prescription drugs can represent one of the largest healthcare expenses in retirement — yet Medicare Part A and Part B cover almost none of them. Medicare Part D is the program that fills this gap, offering prescription drug coverage through private insurance plans approved by Medicare.

Understanding how Part D works, what it costs, and how to choose the right plan can save you hundreds or thousands of dollars a year. This guide covers everything you need to know about Medicare Part D in 2026 — including the new $2,100 out-of-pocket cap, the $35 insulin limit, and the free vaccines that came out of the Inflation Reduction Act.

What Is Medicare Part D?

Medicare Part D is the prescription drug coverage component of Medicare. It is offered through private insurance companies that have contracted with Medicare, not directly from the federal government.

Part D plans come in two forms:

1. Standalone Part D plans (PDPs): If you have Original Medicare (Parts A and B) and want drug coverage, you add a standalone Part D plan to your existing coverage.
2. Medicare Advantage with Part D (MAPD): Most Medicare Advantage plans bundle Part D drug coverage. If you have an Advantage plan that includes drug coverage, your drugs are covered through that plan — you don’t buy a separate Part D plan.

Part D is optional, but there’s a significant catch: if you go without creditable drug coverage for 63 or more consecutive days after becoming Medicare-eligible, you’ll face a permanent late-enrollment penalty when you do eventually enroll.

How Part D Works

Every Part D plan has a formulary — a list of covered drugs. Drugs on the formulary are organized into tiers, with lower tiers generally meaning lower cost-sharing for you:

• Tier 1: Preferred generic drugs (lowest cost)
• Tier 2: Non-preferred generics and some lower-cost brand-name drugs
• Tier 3: Preferred brand-name drugs
• Tier 4: Non-preferred brand-name drugs (higher cost)
• Tier 5: Specialty drugs (highest cost — often biologics and specialty medications)

Your cost for each drug depends on the tier, the plan’s deductible, and whether you’ve reached certain spending thresholds during the year.

Plans also use three tools to manage how drugs are dispensed, and all three can affect whether you can fill a prescription as written:

• Prior authorization — the plan must approve certain drugs before it will pay, usually requiring your doctor to document medical necessity.
• Step therapy — you may be required to try a lower-cost drug first and show it didn’t work before the plan covers a more expensive alternative.
• Quantity limits — the plan caps how much of a drug it will cover in a given period.

If one of these rules blocks a drug you need, you have the right to request an exception — see Coverage Exceptions and Appeals below.

The Part D Coverage Phases in 2026

Part D coverage works in spending stages. The rules changed significantly in 2025 under the Inflation Reduction Act — eliminating the old coverage gap (the “donut hole”) and adding a hard out-of-pocket cap — and those changes carry into 2026 with slightly higher dollar thresholds.

Deductible Phase

Most Part D plans charge an annual deductible before coverage begins. In 2026, the maximum allowed deductible is $615 for standard plans (up from $590 in 2025). Some plans waive the deductible for certain tiers, often Tier 1 generics.

During the deductible phase, you pay 100% of the negotiated drug cost until you’ve paid $615.

Initial Coverage Phase

After meeting your deductible, you pay your plan’s standard cost-sharing — copays or coinsurance — for each drug. This phase continues until your out-of-pocket spending reaches the annual cap.

Catastrophic Coverage Phase

Once your out-of-pocket drug spending reaches $2,100 in a calendar year (up from $2,000 in 2025), your Part D plan covers 100% of all covered drug costs for the rest of the year. There is no further cost-sharing until January.

This $2,100 out-of-pocket cap is the single most important improvement for people who take expensive medications. Before 2025, there was no annual limit at all, and enrollees on specialty drugs could spend many thousands of dollars a year.

A Worked Example Through the Phases

Suppose you take one specialty drug with a negotiated price of $1,000 per month in 2026, on a plan with the standard $615 deductible and 25% coinsurance in the initial coverage phase. Here’s how your year plays out:

• Deductible phase: You pay the first $615 yourself.
• Initial coverage phase: You then pay 25% coinsurance. To climb from $615 to the $2,100 cap, you need to pay another $1,485 out of pocket — which at 25% covers about $5,940 of drug cost.
• By roughly the middle of the year, your out-of-pocket spending hits $2,100.
• Catastrophic phase: For every month afterward, you pay $0.

Your total out-of-pocket cost for the entire year is capped at $2,100, no matter how expensive the drug is — a guarantee that simply did not exist before 2025.

What Part D Does Not Cover: The Part B vs. Part D Split

One of the most expensive and misunderstood corners of Medicare is which part pays for which drug. Part D covers the medications you pick up at a pharmacy and take yourself — pills, most self-injected drugs, inhalers. But drugs that are infused or injected in a clinic or doctor’s office are usually covered by Part B, not Part D.

This distinction matters enormously because Part B has no annual out-of-pocket cap. You generally pay 20% of the cost with no ceiling unless you have Medigap or a Medicare Advantage plan’s out-of-pocket maximum. So the same condition can cost wildly different amounts depending on whether your treatment is a pill (Part D, capped at $2,100) or an infusion (Part B, uncapped 20%).

This split drives the cost story in nearly every expensive condition — from cancer treatment (oral targeted pills vs. infused immunotherapy) to rheumatoid arthritis biologics (self-injected vs. IV-infused). It’s worth reading our dedicated guide on the Part B vs. Part D drug coverage split before any major treatment decision, because the route of administration can change your annual cost by thousands of dollars.

What Does Part D Cost in 2026?

Your total Part D costs include several components.

Monthly Premium

Part D premiums vary by plan and by state. Nationally, the average standalone Part D plan premium is projected at roughly $34.50 per month in 2026 — down slightly from 2025 — though individual plans range from $0 to well over $100 per month.

Higher-income beneficiaries pay a Part D IRMAA surcharge on top of their plan premium, based on income from two years earlier:

The IRMAA surcharge is paid directly to Medicare (added to your Part B premium bill), not to your Part D plan. For the full income brackets, married-couple figures, and how to appeal after a life-changing event, see our IRMAA surcharges guide.

Annual Deductible

Up to $615 per year for standard plans in 2026. Many plans charge less; some waive it for certain drug tiers.

Copays and Coinsurance

After the deductible, you pay a copay or coinsurance for each prescription. Copays for Tier 1 generics are often as low as $0–$5. Brand-name drugs can have coinsurance of 25%–50%, and specialty drugs may have coinsurance that quickly drives you toward the out-of-pocket cap.

Out-of-Pocket Maximum

Once you’ve spent $2,100 out of pocket on covered drugs in 2026, your plan pays 100% for the rest of the year.

Two Big Inflation Reduction Act Wins

Beyond the $2,100 cap, two more changes from the Inflation Reduction Act directly lower what Part D enrollees pay at the pharmacy.

The $35 Insulin Cap

Every covered insulin product under Part D is capped at $35 for a one-month supply — and there is no deductible on insulin. This applies whether you’re in the deductible phase or the initial coverage phase, so a person with diabetes pays no more than $35 a month per covered insulin regardless of the list price.

Free Recommended Vaccines

Vaccines recommended for adults by the Advisory Committee on Immunization Practices (ACIP) — including shingles (Shingrix), Tdap, and RSV — are now covered by Part D at $0 out of pocket. Before 2023, the shingles vaccine alone could cost a beneficiary $150–$200.

The Late-Enrollment Penalty

If you don’t have creditable prescription drug coverage and delay enrolling in Part D, you’ll pay a permanent penalty.

The penalty is 1% of the national base beneficiary premium ($38.99 in 2026) for each full month you were eligible but not enrolled. This is added to your monthly Part D premium for as long as you have Part D coverage, and the base premium it’s tied to rises most years — so the penalty grows over time.

Example: If you delay enrollment for 24 months, your penalty is 24% × $38.99 ≈ $9.36 per month, added to every monthly premium you pay, for life.

What Counts as Creditable Coverage

Coverage is “creditable” if it’s at least as good as standard Part D coverage. Creditable coverage includes:

• Employer or union group health plan drug coverage
• TRICARE (military retiree coverage)
• VA health benefits
• Individual health insurance drug coverage
• Most COBRA coverage with drug benefits

Your insurer must notify you annually whether your coverage is creditable. Keep these notices in case you need to prove your coverage history to Medicare later. If you’re working past 65 with employer drug coverage, confirm in writing that it’s creditable before deciding to delay Part D.

The Medicare Prescription Payment Plan

New under the Inflation Reduction Act and continuing in 2026, the Medicare Prescription Payment Plan (sometimes called “M3P” or drug-cost smoothing) lets you spread your Part D out-of-pocket costs across the calendar year in monthly installments rather than paying large amounts at the pharmacy counter.

It does not lower your total cost — you still owe up to the $2,100 cap — but it changes the timing. Instead of paying, say, $1,000 in January and February when an expensive drug pushes you through the deductible, you’d pay nothing at the pharmacy and receive monthly bills from your plan that spread that $2,100 more evenly across the year.

This is most useful for people who hit their costs early in the year and would otherwise struggle with a large upfront bill. Participation is optional and free, and you opt in through your Part D or Medicare Advantage drug plan.

When Can You Enroll in Part D?

Initial Enrollment Period (IEP)

Your first opportunity to enroll in Part D is the 7-month Initial Enrollment Period around your 65th birthday — the same window as Part B. Enrolling promptly avoids the late-enrollment penalty. See our full guide to Medicare enrollment periods.

Annual Enrollment Period (AEP)

From October 15 to December 7 each year, you can switch Part D plans for the following year. This is the main window to review your current plan and change if a different plan covers your drugs better — and because formularies and premiums change every year, it’s worth doing annually. Our annual enrollment guide walks through the review step by step.

Medicare Advantage Open Enrollment Period

From January 1 to March 31 each year, Medicare Advantage enrollees can switch plans or return to Original Medicare (and then add a standalone Part D plan).

Special Enrollment Periods (SEPs)

You can enroll outside the standard windows if you experience qualifying events: losing creditable coverage, moving to a new address, or qualifying for Extra Help (the low-income subsidy program). People with Extra Help also get a quarterly opportunity to change plans.

How to Choose a Part D Plan

With dozens of plans available in most areas, comparing options carefully is essential. The right plan depends on which drugs you take.

Step 1: List Your Medications

Before comparing plans, compile a complete list of every prescription drug you take, including the name (brand and generic), dosage, and how often you take it.

Step 2: Use Medicare’s Plan Finder

Medicare’s official Plan Finder tool (at Medicare.gov) lets you enter your ZIP code and drug list to compare all available plans based on your total annual cost — premium plus out-of-pocket drug costs combined. This total-cost view is far more useful than comparing premiums alone.

Step 3: Check the Formulary

Verify that each drug you take is covered on the plan’s formulary and at what tier. If a drug is on a high tier, excluded, or subject to prior authorization or step therapy, your annual costs could be much higher than the Plan Finder estimates.

Step 4: Consider the Pharmacy Network

Part D plans have preferred pharmacy networks. Using a preferred pharmacy often means lower copays. If you use mail-order for maintenance drugs, verify the plan’s mail-order options and pricing.

Step 5: Account for Deductibles

If you take low-cost generics, a plan with a $0 deductible for Tier 1 drugs may save you money even if its premium is slightly higher.

Coverage Exceptions, Prior Authorization, and Appeals

If your plan won’t cover a drug you need — because it’s off the formulary, on a high tier, or blocked by prior authorization or step therapy — you have the right to ask for an exception. Your prescriber submits a statement explaining why you need that specific drug, and the plan must respond within 72 hours for a standard request, or 24 hours for an expedited (urgent) request.

If the plan denies the exception, Medicare gives you a five-level appeals process:

1. Redetermination by the plan
2. Reconsideration by an independent review entity
3. Hearing before an Administrative Law Judge
4. Review by the Medicare Appeals Council
5. Judicial review in federal court

Most issues are resolved at the first or second level. Don’t simply pay full price or go without a needed drug — the exception and appeal rights exist precisely for these situations, and they’re free to use.

Extra Help: The Part D Low-Income Subsidy

If your income and assets are limited, you may qualify for Extra Help (also called the Low-Income Subsidy or LIS), a federal program that helps pay Part D premiums, deductibles, and copays.

In 2026, Extra Help is generally available to people with:

• Individual income up to about $23,475 per year (roughly $31,725 for a married couple) — at or below 150% of the federal poverty level
• Resources below about $17,220 for individuals ($34,360 for couples) — excluding your home, one car, and certain other assets

With full Extra Help in 2026, your deductible is $0, generic copays run about $1.60–$4.90 and brand copays about $4.90–$12.65, and you pay $0 once you reach the out-of-pocket cap. Extra Help also eliminates or significantly reduces the late-enrollment penalty, even if you’ve delayed enrollment.

If you think you might qualify, apply through the Social Security Administration (SSA.gov) or your state Medicaid office. It’s also worth checking whether you qualify for a Medicare Savings Program, which can pay your Part B premium — qualifying for one often automatically qualifies you for Extra Help.

Part D and Medicare Advantage

If you have Medicare Advantage rather than Original Medicare, check whether your plan includes drug coverage (most do). If it does, you receive your Part D benefits through your Advantage plan — you don’t need a separate Part D plan, and enrolling in one could actually disenroll you from your Advantage plan.

If your Medicare Advantage plan doesn’t include drug coverage, you may be able to add a standalone Part D plan, but this depends on the specific Advantage plan.

Frequently Asked Questions

Do I need Part D if I don’t take any prescriptions? It’s still usually worth enrolling in a low-cost plan when you’re first eligible. Drug needs are unpredictable, and the late-enrollment penalty is permanent — a cheap plan now protects you against both a future medical need and a lifelong penalty.

Does the $2,100 cap include my premiums? No. The $2,100 cap counts your out-of-pocket spending on covered drugs (deductible, copays, and coinsurance). Your monthly premium is separate and doesn’t count toward the cap.

Can I have both a standalone Part D plan and Medicare Advantage? Generally no. If your Medicare Advantage plan includes drug coverage, joining a separate Part D plan will usually disenroll you from the Advantage plan and return you to Original Medicare.

What happens to my drug costs if I travel or move? Part D plans have regional networks. If you move out of your plan’s service area, that triggers a Special Enrollment Period to switch plans. Snowbirds should confirm mail-order and out-of-area pharmacy access — see our snowbird guide.

Key Takeaways

• Medicare Part D covers prescription drugs through private plans approved by Medicare — but drugs infused in a clinic are usually Part B, not Part D
• In 2026, your out-of-pocket drug costs are capped at $2,100 per year — after that, the plan pays 100%
• Insulin is capped at $35/month and recommended adult vaccines are free under the Inflation Reduction Act
• The late-enrollment penalty is 1% per month of delay, permanent, and tied to the $38.99 base premium — don’t skip Part D if you have no other creditable coverage
• Annual Enrollment Period (October 15–December 7) is your chance to switch plans each year — review your coverage every year, since formularies and premiums change
• Use Medicare’s Plan Finder at Medicare.gov to compare total annual costs (premium + drugs), not just premiums

For the full picture of how Part D fits with your other Medicare coverage, see our guides on Original Medicare vs. Medicare Advantage, Medigap plan comparisons, and the all-important Part B vs. Part D drug split. For how drug costs fit your broader budget, see healthcare costs in retirement.

Sources

• Medicare.gov — Drug coverage (Part D)
• Medicare.gov — Medicare Plan Finder
• Medicare.gov — Medicare costs
• CMS.gov — 2026 Medicare Parts A & B premiums and deductibles (fact sheet)

All sources are official government or nonprofit consumer resources, verified July 2026. Medicare and Social Security rules and dollar amounts change annually — confirm current figures at the links above before making decisions.