What Is Medicare Part D and Do You Really Need It?

Medicare Part D is the part of Medicare that covers prescription drugs, and it’s the piece most people don’t pay enough attention to until they’re standing at the pharmacy paying full price. What is Medicare Part D, exactly? It’s outpatient prescription drug coverage delivered through private insurance plans approved by Medicare. It’s optional in the sense that you don’t have to enroll, but skipping it without having other qualifying drug coverage comes with a permanent financial penalty that’s harder to escape than most people expect.

Here’s how Part D works, what it costs, and why the decision to skip it deserves careful thought.

How Does Medicare Part D Work?

Medicare Part D works by giving you access to a private insurance plan that covers a defined list of prescription drugs, called a formulary, at negotiated prices. You pay a monthly premium, an annual deductible if your plan has one, and a share of each prescription’s cost through copays or coinsurance.

Part D coverage comes in two forms. If you’re enrolled in Original Medicare (Parts A and B), you add a standalone Part D plan to your coverage. If you’re enrolled in Medicare Advantage, most Medicare Advantage plans include Part D drug coverage built in, which means you don’t need a separate plan.

One of the most significant changes to Part D in recent years took effect in 2025: the Medicare coverage gap, long known as the donut hole, was permanently eliminated. The multi-phase spending structure now has a clear ceiling. In 2025, your maximum out-of-pocket spending on covered Part D drugs is capped at $2,000 per year, according to KFF.

Once you hit that threshold, your plan covers 100% of covered drug costs for the rest of the year. This is a significant protection, particularly for people who take specialty or high-cost medications.

What Does Medicare Part D Actually Cover?

Medicare Part D covers outpatient prescription drugs, meaning medications you pick up at the pharmacy or receive through mail order, not drugs administered in a hospital or doctor’s office. Part D plans are required to cover at least two drugs in each therapeutic category, but the specific drugs covered, and the tier at which they’re covered, vary by plan.

Every Part D plan publishes a formulary listing all covered drugs and their cost tier. Tier 1 typically includes preferred generics at very low or no copay. Tier 2 covers non-preferred generics. Tiers 3 and above cover brand-name and specialty drugs at progressively higher cost-sharing rates.

Part D also covers most recommended vaccines not covered by Part B, including the shingles vaccine, which costs several hundred dollars without coverage. This is a benefit many enrollees overlook when calculating whether Part D is worth the premium.

The average monthly premium for a standalone Part D plan is approximately $35 in 2025, according to CMS data. Some plans are available well below that amount, particularly for people willing to compare options during Open Enrollment rather than auto-renewing their current plan.

What Is the Medicare Part D Late Enrollment Penalty?

The Part D late enrollment penalty is a permanent monthly surcharge added to your premium if you go 63 or more consecutive days without creditable prescription drug coverage after your Initial Enrollment Period ends. This is the single most important reason not to skip Part D carelessly.

The penalty is calculated as 1% of the national base beneficiary premium, which is $38.99 in 2026, multiplied by the number of uncovered months. A two-year gap, 24 months without coverage, adds roughly $9 per month permanently to your premium. That’s not enormous, but it never goes away, and it compounds if the national base premium rises over time.

Creditable coverage means coverage at least as good as standard Part D. Employer group drug plans, VA drug benefits, and TRICARE typically qualify. The key word is “creditable,” and it’s worth confirming in writing from your coverage provider before you skip Part D enrollment.

Jonathan Potter frequently works with clients approaching 65 who are tempted to skip Part D because they take few medications currently. His standard advice: even if your current drug costs are low, enrolling in a low-premium plan protects you from the penalty and covers you if your medication needs change. Review your Medicare coverage options before your Initial Enrollment Period closes to avoid a cost that follows you permanently.

How Do You Enroll in Medicare Part D?

You enroll in Medicare Part D during your Initial Enrollment Period, which is the seven-month window around your 65th birthday, or during the Medicare Annual Enrollment Period from October 15 to December 7 each year.

During your Initial Enrollment Period, you can sign up for a standalone Part D plan through medicare.gov, by calling 1-800-MEDICARE, or through a licensed broker who can compare plans in your area and run your specific medications through each plan’s formulary. The broker comparison step is genuinely useful here. Formularies differ significantly between plans, and a medication that’s a $10 copay on one plan might be $80 on another.

Outside of your initial enrollment window, you can add or switch Part D plans during the Annual Enrollment Period each October and November. If you have a qualifying life event, such as losing other creditable drug coverage, you may be eligible for a Special Enrollment Period.

Should You Enroll in Part D Even If You Don’t Take Prescriptions?

Yes, in most cases. Taking no prescriptions today is not the same as taking no prescriptions tomorrow. The late enrollment penalty applies regardless of how healthy you are at 65, and the cost of a low-premium Part D plan is modest compared to the penalty you’d carry if you delayed and then needed coverage later.

The exception is if you have creditable drug coverage from another source, such as employer retiree coverage or VA benefits. In that case, you can delay Part D enrollment without penalty as long as the other coverage remains in place. If that coverage ever ends, you have 63 days to enroll before the penalty clock starts.

Every situation has nuances, and the right decision depends on your specific coverage picture. Connect with Beacon Insurance Advisors to review your Part D options before your enrollment window closes.

FREQUENTLY ASKED QUESTIONS

What happens if I miss my Medicare Part D enrollment window?

If you go 63 or more consecutive days without creditable prescription drug coverage after your Initial Enrollment Period, you’ll face a permanent late enrollment penalty added to your monthly premium when you eventually do enroll. You’ll also need to wait for the next Annual Enrollment Period to sign up unless you qualify for a Special Enrollment Period.

Can I change my Part D plan after I enroll?

Yes. You can switch Part D plans during the Medicare Annual Enrollment Period, which runs from October 15 to December 7 each year. Changes take effect January 1. It’s worth comparing your current plan against available options each year, since formularies and premiums change annually.

Does Medicare Part D cover insulin?

Yes. Since 2023, Medicare Part D plans are required to cap cost-sharing for insulin at $35 per month per covered insulin product. This applies regardless of which coverage phase you’re in during the year. It’s one of the most meaningful cost protections for diabetic Medicare beneficiaries under recent drug pricing legislation.

Medicare Part D is optional in name but essential in practice for most people turning 65. The late enrollment penalty is permanent, the donut hole is gone, and the $2,000 annual out-of-pocket cap introduced in 2025 makes Part D a better deal than it’s ever been. Review your Medicare and Part D options before your enrollment window closes.