How to Evaluate Medicare Part D Plans (And Avoid the Worst Ones)

If you've ever tried to help a parent pick a Medicare prescription drug plan and walked away more confused than when you started, you're not alone. The Part D marketplace is deliberately opaque, and the plans most heavily marketed are not always the ones best suited to your parent's actual medications.

The uncomfortable truth: research consistently shows that fewer than 10% of Medicare beneficiaries successfully identify the cheapest plan that covers their specific drug regimen. The rest overpay — often by hundreds of dollars per year — simply because they chose based on the wrong criteria.

This guide explains how to evaluate Part D plans methodically, and what the red flags of a poor-quality plan actually look like.

Why "Worst" and "Best" Depends on Your Parent's Medications

There is no universally bad Part D plan. A plan that is terrible for one person's drug list may be excellent for someone else's. This is why lists claiming to rank "the 10 worst Medicare Part D plans" are mostly noise — they can't account for the individual formulary match.

What actually makes a plan bad for your parent:

• Their specific drugs are on a high tier (Tier 4 or 5 specialty instead of Tier 1 or 2 generic)
• Their preferred pharmacy is "non-preferred" in the plan's network, triggering higher cost-sharing
• The plan's deductible is high and applies to most drug tiers
• Coverage restrictions: step therapy (must try a cheaper drug first), prior authorization for drugs they already take
• Low Star Rating: plans rated under 3.5 stars by CMS have documented quality problems

The only way to know if a plan is bad for your parent is to run their specific drug list through the Medicare Plan Finder.

The $2,000 Out-of-Pocket Cap Changes the Math in 2026

Starting in 2025, the Inflation Reduction Act capped what any Medicare beneficiary pays out of pocket for Part D drugs at $2,000 per year (the cap rises slightly to $2,100 in 2026). This replaces the old "donut hole" structure that exposed seniors to uncapped catastrophic drug costs.

This is good news for anyone on high-cost medications like cancer drugs, rheumatoid arthritis biologics, or MS treatments. But it also means the premium comparison math has shifted — for seniors with high drug costs, the $2,000 cap limits their downside regardless of which plan they choose, so the difference between plans comes down to total premiums plus how quickly they hit that cap.

For parents on only a handful of cheap generics, the cap is less relevant and plan selection comes down to minimizing combined premium and formulary costs.

Step-by-Step: How to Compare Part D Plans Objectively

Step 1: Build the Complete Drug List

Write down every medication your parent takes:

• Exact drug name (generic and brand name if different)
• Exact dosage (e.g., metformin 1000mg — not just "metformin")
• How often they take it (once daily, twice daily, as needed)
• Their current pharmacy

Incomplete lists produce inaccurate comparisons. A missing drug that happens to be Tier 5 specialty could mean a $200/month surprise.

Step 2: Use Medicare.gov Plan Finder — Not a Broker's Website

Go to medicare.gov/plan-compare. Log into your parent's MyMedicare.gov account (or create one). Logging in allows the tool to pull their existing prescription history from claims data, which helps catch medications they might have forgotten to mention.

Enter the drug list. Enter the preferred pharmacy. The tool will calculate the Total Annual Cost for every available plan — which includes premiums, deductibles, and the expected drug cost-sharing based on your parent's specific formulary situation.

Step 3: Sort by Total Annual Cost, Not Premium

This is the most common mistake families make. A plan with a $0 monthly premium sounds appealing. But if that plan places your parent's blood pressure medication on Tier 4 instead of Tier 2, the annual copay difference can easily exceed what they'd spend on a plan with a $45/month premium.

Always sort by "Estimated Annual Drug + Premium Cost." That number is the only meaningful comparison.

Step 4: Check the Deductible Structure

Many Part D plans have a deductible that applies before coverage kicks in. In 2026, the maximum allowable deductible is $590. Some plans waive the deductible for Tier 1 and Tier 2 drugs (generics). Others apply the full deductible across all tiers.

If your parent's drugs are mostly generics, a plan with a waived deductible on lower tiers can save hundreds upfront each year.

Step 5: Check Pharmacy Network Status

Even within the same plan, cost-sharing varies by pharmacy. Most Part D plans have "preferred" and "standard" pharmacies. Using a preferred pharmacy (often a specific major chain or a mail-order option) can reduce copays by $5–$30 per prescription.

If your parent's neighborhood pharmacy is "standard" rather than "preferred," compare what it would cost to switch their prescriptions to a preferred pharmacy or mail-order. For 90-day supplies of maintenance drugs, mail-order is usually the lowest cost option.

Step 6: Read the Coverage Restrictions

For any plan you're seriously considering, check whether your parent's specific drugs require:

• Prior authorization: Plan must approve the drug before they'll cover it
• Step therapy: Must try a cheaper alternative first
• Quantity limits: Plan only covers a 30-day supply when their doctor prescribed 90 days

These restrictions aren't always visible upfront on the Plan Finder summary. Click into the plan details and look up each drug individually in their formulary viewer.

Red Flags That Signal a Poor Plan

These signs don't automatically disqualify a plan, but they warrant closer scrutiny:

Star rating below 3.5: CMS rates Part D plans on appeals handling, customer service, accuracy, and drug safety. Plans with fewer than 3.5 stars have documented problems. Check the star rating for any plan you're considering — it's shown on the Plan Finder.

No coverage for specialty tiers at all: Some plans simply exclude Tier 5 specialty drugs or cap coverage at a low dollar amount. If your parent currently takes or may need a specialty drug, this is a critical issue.

Extremely low premium with high deductible: A $0 premium plan with a $590 deductible and standard-only pharmacy access is often worse than a $35/month plan with no deductible and preferred pharmacy pricing.

Brand-only plan without strong generic pricing: If your parent is on mostly generics and the plan has a complex, expensive tier structure for generic tiers, keep looking.

The Late Enrollment Penalty: Don't Skip Part D

One costly mistake adult children sometimes make is encouraging a parent to skip Part D enrollment at 65 because "they don't take many medications right now." The problem is the late enrollment penalty.

For every month your parent goes without creditable drug coverage after becoming eligible for Part D, they owe an additional 1% of the national base beneficiary premium — permanently. At the 2026 base premium of $38.99, a 36-month delay adds roughly $14/month to their Part D premium for the rest of their life. Over 20 years, that's over $3,360 for the mistake of skipping enrollment when they were healthy.

Even if your parent takes no medications, enrolling in a low-cost Part D plan (often $10–$20/month) protects them from this permanent penalty.

What to Do If a Drug Gets Dropped Mid-Year

If a plan removes a drug from its formulary mid-year (which is allowed in some circumstances), your parent has protections:

1. Request an exception: Ask the plan's coverage determination process to make an exception based on medical necessity. Their doctor will need to submit documentation.
2. File an appeal: If the exception is denied, you can appeal through the plan and then to an independent review entity.
3. Use a Special Enrollment Period: If the formulary change constitutes a reduction in covered benefits, it may trigger an SEP to switch plans outside the normal OEP window.

Getting It Right Matters More Than Getting It Perfect

Part D selection doesn't need to be perfect — it needs to be informed. Spending two hours with the Medicare Plan Finder before every Annual Enrollment Period (October 15 – December 7) and comparing total annual costs will put your parent in a dramatically better position than the majority of beneficiaries who simply stay in whatever plan they enrolled in at age 65.

For a complete guide covering every piece of Medicare — not just Part D but also the Original Medicare vs. Medicare Advantage decision, Medigap strategies, enrollment windows, and IRMAA income planning — the Medicare Enrollment Guide was written specifically for adult children navigating this on behalf of aging parents.