Medicare Part D Explained: How Prescription Drug Coverage Works in 2025

If you’re turning 65 or already on Medicare, Part D is one decision that can save — or cost — you thousands of dollars per year. Here’s everything you need to know.

What Is Medicare Part D?

Medicare Part D is the federal prescription drug benefit that helps cover the cost of medications. It’s offered through private insurance companies approved by Medicare, and it works alongside your other Medicare coverage — whether you have Original Medicare (Parts A and B) or a Medicare Advantage plan.

Here’s the key thing most people don’t realize: Part D isn’t optional in the long run. If you delay enrolling and don’t have creditable drug coverage elsewhere, you’ll face a permanent late enrollment penalty that follows you for the rest of your Medicare enrollment.

Who Needs Part D?

You should consider Part D if you:

Are turning 65 and enrolling in Medicare
Are currently on a Medicare Supplement (Medigap) plan
Take any prescription medications — even generics
Want protection against high drug costs in the future

You may already have it if you:

Enrolled in a Medicare Advantage plan that includes drug coverage (most do)
Have creditable drug coverage through an employer or union plan

How Part D Works: The Four Coverage Stages

Understanding Part D means understanding its four-stage structure. Each stage affects what you pay.

Stage 1: Deductible Phase

In 2025, the maximum allowable deductible is $590. Many plans have a lower deductible — some are even $0 for preferred generic drugs. During this phase, you pay the full cost of your medications until you’ve met your deductible.

Stage 2: Initial Coverage Phase

Once your deductible is met, you and your plan share costs. You pay copays or coinsurance for covered drugs, and your plan pays the rest. This continues until the total drug costs (what you and the plan paid combined) reach the initial coverage limit.

Stage 3: The Coverage Gap — Goodbye “Donut Hole”

The infamous “donut hole” that Medicare beneficiaries dreaded for years has been significantly reformed. Under the Inflation Reduction Act, your out-of-pocket costs in the gap are now capped at a much lower level than they used to be. In 2025, you’ll pay no more than 25% for brand-name and generic drugs during this phase.

Stage 4: Catastrophic Coverage

Once your out-of-pocket costs reach $2,000 in 2025 (a major improvement from previous years), you enter catastrophic coverage. At this stage, you pay $0 for the rest of the year — your plan covers everything. This is a landmark change that protects seniors with high drug costs from financial devastation.

The Medicare Prescription Payment Plan (M3P)

Starting in 2025, Medicare beneficiaries can opt into the Medicare Prescription Payment Plan, which lets you spread your out-of-pocket drug costs evenly across the calendar year (January–December). Instead of paying a large amount upfront in early months when many prescriptions fill, you pay a consistent monthly amount.

This is especially valuable for people who take expensive medications or have high drug costs in early months.

Choosing the Right Part D Plan

With dozens of plans available in most areas, choosing the right Part D plan requires looking at several factors:

1. Your Formulary (Drug List)

Every Part D plan has a formulary — a list of covered drugs organized into “tiers.” Drugs in lower tiers cost you less. Before choosing a plan, run your specific medications through the plan’s formulary checker to ensure they’re covered and at what tier.

2. Your Pharmacies

Plans have networks of preferred pharmacies where you’ll pay the lowest cost-sharing. Using an out-of-network pharmacy can dramatically increase your costs. Check whether your pharmacy — and mail-order options — are in the plan’s network.

3. The Premium vs. Total Cost Tradeoff

A plan with a $0 premium isn’t always the cheapest. If that plan charges higher copays for your specific drugs, you could spend far more overall than you would on a plan with a modest monthly premium but better drug pricing. Always compare total annual cost, not just the premium.

4. Star Ratings

Medicare rates every Part D plan on a 5-star scale. Higher-rated plans generally have better customer service, fewer complaints, and more accurate pricing information. Look for plans with 4 or 5 stars.

When to Enroll in Part D

Initial Enrollment Period (IEP)

Your first chance to enroll is a 7-month window: 3 months before your 65th birthday month, your birthday month, and 3 months after.

Annual Enrollment Period (AEP)

Every year from October 15 through December 7, you can switch Part D plans for coverage starting January 1. This is your annual opportunity to re-shop based on your current medications and the new year’s plan offerings.

Special Enrollment Periods (SEP)

If you lose creditable drug coverage (like from an employer plan), you generally have 63 days to enroll in Part D without penalty.

The Late Enrollment Penalty

This is where many people get hurt. If you go 63 or more days without creditable drug coverage after you’re first eligible for Medicare, you’ll owe a late enrollment penalty — forever.

The penalty calculation: 1% of the national base beneficiary premium × the number of full months you went without coverage. In 2025, the national base beneficiary premium is $36.78.

For example, if you delayed enrollment for 24 months, your penalty would be approximately $8.83/month added to your Part D premium — for life.

The lesson: Enroll during your Initial Enrollment Period, even if you’re healthy and don’t take medications. The protection is worth the premium.

Part D and Low-Income Subsidy (Extra Help)

If your income and resources are below certain limits, you may qualify for Extra Help (also called the Low-Income Subsidy), a federal program that dramatically reduces your Part D costs:

Much lower or no deductible
Reduced copays for all covered drugs
No coverage gap
A Special Enrollment Period year-round

In 2025, individual income limits for full Extra Help are approximately $22,590/year (subject to annual adjustment). Even partial Extra Help is available at higher income levels. Contact us to see if you qualify — it costs nothing to check.

5 Common Part D Mistakes to Avoid

Not enrolling when first eligible — The penalty is permanent and compounds
Choosing based on premium alone — Total drug cost is what matters
Not re-shopping every October — Plans change formularies, prices, and star ratings annually
Using an out-of-network pharmacy — Can cost 2-3x more per prescription
Forgetting to check for Extra Help — Millions of eligible seniors don’t apply

Part D and Medicare Advantage

If you have a Medicare Advantage plan, it almost certainly already includes Part D coverage. You cannot have a separate standalone Part D plan with most Medicare Advantage plans. The drug coverage is built in and evaluated as part of the overall plan.

When comparing Medicare Advantage plans, pay close attention to the drug formulary — it varies significantly between plans and can have a major impact on your total annual costs.

How We Help You Choose

At Legacy Wealth Services, we work with dozens of Part D and Medicare Advantage carriers to find the plan that fits your specific medication needs and budget. We don’t push one company — we shop the market for you.

Every year, we recommend our clients take advantage of the Annual Enrollment Period to review their coverage. Drug formularies, premiums, and your own medication needs change. A plan that was perfect last year may not be the best choice this year.

Ready to review your Medicare coverage? Schedule a no-cost consultation and we’ll compare your options across multiple carriers in minutes.

Rodney Cummings is a licensed Medicare specialist serving clients across 26 states. Legacy Wealth Services offers Medicare Advantage, Medicare Supplement, and Part D plans from a wide portfolio of leading carriers.