Medicare Part D Prescription Drug Plans: How to Compare Them for an Elderly Parent

Choosing a Medicare Part D prescription drug plan for an elderly parent is not a matter of picking the one with the lowest monthly premium. The premium is often the least important number on the page. What determines actual annual cost is the combination of the deductible, the copays for each specific drug your parent takes, and how the plan's formulary tiers treat those drugs.

The good news: the 2025 and 2026 reforms to Medicare Part D represent the most significant improvements to prescription drug coverage in two decades. The bad news: navigating them still requires understanding a system built on jargon and plan-specific variation. This guide covers what you need to know to compare plans for a senior parent without getting lost in the details.

What Changed for Medicare Part D in 2025 and 2026

Two major changes took effect in 2025 that significantly benefit seniors with high drug costs:

The $2,000 out-of-pocket cap. Starting in 2025, no Part D enrollee pays more than $2,000 per year in out-of-pocket prescription costs for covered drugs. Once that threshold is reached, all covered drugs cost $0 for the rest of the year. For parents on expensive specialty medications — biologics, cancer drugs, multiple sclerosis treatments — this cap is transformative. Previously, some beneficiaries paid $5,000 or more annually.

The Medicare Prescription Payment Plan (M3P). Also called the "smoothing" option, this allows beneficiaries to spread their $2,000 out-of-pocket maximum across monthly installments throughout the year, rather than paying large lump sums in January and February when deductibles reset. This is optional and must be elected, but it significantly helps seniors on fixed incomes who might otherwise skip doses in early months to manage cash flow.

The "donut hole" (coverage gap) that previously existed between the initial coverage phase and catastrophic coverage has been structurally eliminated for 2025. The benefit is now simpler: deductible phase, initial coverage phase, and then the $2,000 cap triggers free coverage.

The Difference Between Stand-Alone Part D Plans and Medicare Advantage Drug Coverage

If your parent is on Original Medicare (Parts A and B only), they need a stand-alone Part D plan (sometimes called a PDP) to get prescription drug coverage. These plans are sold by private insurers and cover only drugs — not hospital or medical costs.

If your parent has Medicare Advantage, their plan likely includes drug coverage (MA-PD plans). In that case, they do not need a separate Part D plan, and cannot enroll in one.

Understanding which category your parent is in determines what you are shopping for:

• Original Medicare + Medigap: Needs a stand-alone Part D plan
• Medicare Advantage with drug coverage: Already has Part D built in
• Medicare Advantage without drug coverage: Rare, but can enroll in a stand-alone PDP

The Five Numbers That Actually Determine Plan Cost

When comparing Part D plans, these five numbers determine what your parent will actually pay:

1. The Deductible

The maximum Part D deductible in 2026 is $590. Many plans charge the full deductible; some charge less; some charge $0. However, a plan with a $0 deductible and a higher premium is not automatically better. You need to run the math against your parent's specific drug list.

2. The Monthly Premium

The premium is what you pay regardless of drug use. Premiums vary widely — from under $10/month to over $100/month for the same geographic area. Do not choose based on premium alone.

3. The Formulary Tier

Every Part D plan organizes covered drugs into tiers. Typically:

• Tier 1: Preferred generics — lowest copay
• Tier 2: Non-preferred generics — slightly higher copay
• Tier 3: Preferred brand-name drugs
• Tier 4: Non-preferred brand-name drugs — high copay
• Tier 5: Specialty drugs — highest cost share (percentage-based)

Whether your parent's specific drugs are on Tier 1 or Tier 4 can mean a difference of hundreds of dollars per year, per drug. A plan with a high premium but all your parent's drugs on Tier 1 may cost less overall than a low-premium plan that puts those same drugs on Tier 3.

4. Copays vs. Coinsurance for Each Drug

Some plans charge flat copays (e.g., $12 per fill). Others charge coinsurance — a percentage of the drug's cost (e.g., 25%). For expensive drugs, percentage-based coinsurance is far more costly than flat copays, even after the deductible is met.

5. Pharmacy Network

Preferred pharmacy networks matter. A plan may offer lower copays at "preferred" pharmacies in their network. If your parent uses a specific pharmacy for delivery or consolidation purposes, verify that it is in-network — and ideally a preferred network pharmacy — for any plan you are considering.

How to Compare Part D Plans: The Right Tool

The Medicare Plan Finder at Medicare.gov is the correct tool for comparison. Do not compare plans by looking at brochures or insurer websites. The Plan Finder allows you to:

1. Enter your parent's ZIP code
2. Enter their specific medications (drug name, dose, and frequency)
3. Enter their preferred pharmacy
4. See estimated annual cost for each available plan

The estimated annual cost is the number that matters. It combines premium, deductible, and drug-specific copays based on your parent's actual medication list. This is the only apples-to-apples comparison available.

When you run the search, sort by "estimated annual drug costs" rather than "lowest premium." The results will often surprise you: a plan with a $45/month premium may be cheaper overall than one with a $12/month premium, because the expensive drug your parent takes costs 60% less in copays on the higher-premium plan.

Discount Medications for Seniors: When Part D Is Not the Cheapest Option

Here is a counterintuitive fact: for some specific generic drugs, the price through GoodRx or other discount programs may be lower than the Part D copay — even after the deductible is met. This is legal and allowed, but using a discount card means the purchase does not count toward your parent's Part D out-of-pocket maximum.

The calculus:

• If your parent takes mostly inexpensive generics and has low total drug costs: Discount programs like GoodRx, Cost Plus Drugs (Mark Cuban's pharmacy), or RxSaver may reduce costs on individual drugs, but buying outside Part D means none of it counts toward the $2,000 cap.
• If your parent takes one expensive specialty medication: The Part D $2,000 cap is extremely valuable. Even if generics cost more through Part D copays, the protection against catastrophic specialty drug costs makes full Part D enrollment worthwhile.

For parents on expensive biologics or cancer medications, always use Part D and pursue the $2,000 cap. For parents on exclusively low-cost generics with total annual drug costs under $2,000, a combination of low-premium Part D enrollment (to maintain creditable coverage) plus discount programs for specific drugs may produce the lowest total cost.

Medicare Extra Help: The Program Most Eligible Seniors Never Apply For

Extra Help — also called the Low-Income Subsidy (LIS) — is a federal program that dramatically reduces Part D costs for beneficiaries with limited income and assets.

2025 eligibility thresholds:

• Full Extra Help: Individual income up to approximately $22,590/year (150% of Federal Poverty Level)
• Partial Extra Help: Slightly higher income levels

What Extra Help provides:

• $0 deductible
• $4.50 copay for generics (full Extra Help)
• $11.20 copay for brand-name drugs (full Extra Help)
• No coverage gap

Extra Help is applied for through the Social Security Administration (SSA), not through Medicare. The application can be completed online at ssa.gov, by phone, or in person at an SSA office.

Many families assume their parent would not qualify based on a rough sense of their income. The income thresholds are higher than most people expect, and asset calculations exclude the primary home, one car, personal property, and life insurance policies. Have your parent apply regardless of whether you think they will qualify. The SSA makes the determination.

If your parent qualifies for Medicaid, they automatically qualify for Extra Help — no separate application is needed.

The Medicare Drug Negotiation Program

The Inflation Reduction Act authorized Medicare to directly negotiate drug prices with manufacturers for the first time in the program's history. The first ten negotiated drugs — including some common diabetes and blood pressure medications — took effect in 2026, with prices ranging from 38% to 79% lower than previous Medicare rates.

The negotiated prices apply only when purchasing through Medicare Part D, not through private insurance or discount cards. For parents on the negotiated drugs, this represents a significant reduction in annual costs that shows up automatically in the Plan Finder's estimated cost calculations.

The list of negotiated drugs will expand each year through 2030 as the program phases in additional medications.

Prescription Drug Discount Cards: A Supplement, Not a Replacement

GoodRx, RxSaver, NeedyMeds, and similar programs negotiate discounts with pharmacies directly. They can be useful tools but are not a substitute for Part D enrollment.

Important limitations:

• Purchases using discount cards do not count toward the Medicare out-of-pocket maximum
• Using a discount card instead of insurance on a drug means that drug does not count toward the $2,000 cap
• Some discount card prices are competitive for generics but not for brand-name or specialty drugs

For most seniors with complex regimens, discount cards are best used tactically: for a specific generic drug where the discount price is meaningfully lower than the Part D copay, when the total annual drug cost is already low, and when the parent is not at risk of needing specialty drugs.

When to Review the Plan (Every Year)

Part D plans change their formularies every year. A drug that was on Tier 2 last year may move to Tier 4 this year. A pharmacy that was preferred last year may no longer be in network. The premium and deductible amounts change annually.

Open Enrollment runs October 15 through December 7 each year, with coverage taking effect January 1. During this window, run your parent's drug list through the Medicare Plan Finder every year — even if you are not planning to switch. You may find a better option. If not, staying in the current plan is one click away.

Keeping Track of What the Plan Covers

Even after selecting the best plan, caregivers need to track how coverage interacts with the actual medication list throughout the year — especially as doctors add, remove, or change prescriptions. Each change in the drug list is an opportunity to verify the new drug is on the formulary and to understand what tier it falls on.

The Medication Management Kit includes a prescription coverage tracker that maps each medication to its plan tier, copay, and refill schedule, so you can manage both the clinical and financial dimensions of your parent's medication regimen in one place.