How to Compare Medicare Part D Plans

Why the premium is the wrong thing to shop on

Every Part D plan has four moving parts, and the monthly premium is only one of them. Two plans with identical premiums can cost you hundreds of dollars apart over a year, because the difference is buried in how each one treats the specific drugs you take. A plan advertising a $0 or rock-bottom premium can put your medication on a high tier, or leave it off entirely, and quietly become the most expensive option you could have picked. The number that matters is your total yearly cost, and you can only see it once you match a plan against your own drug list.

The four things that actually differ between plans

• The formulary (drug list). Which of your medications the plan covers, and on which cost tier. This is the biggest lever — a plan that covers your drug on a low tier beats a cheaper plan that doesn't.
• The deductible. What you pay before the plan starts sharing costs. For 2026 no plan can charge more than $615, and some charge $0. A higher deductible can still win overall if the plan covers your drugs better.
• Copays and coinsurance. What you pay per prescription after the deductible — typically 25% coinsurance in the standard design — and it varies by drug tier and by pharmacy.
• The pharmacy network. Most plans have preferred pharmacies with lower copays. The same plan can cost noticeably more at a non-preferred drugstore, so the pharmacy you use is part of the comparison.

What changed for 2026 — the out-of-pocket cap

There's now a hard ceiling on what Part D can cost you. In 2026, once your out-of-pocket spending on covered drugs reaches $2,100, you pay nothing more for covered drugs for the rest of the calendar year. (That cap was $2,000 when it first took effect in 2025; it rises with drug costs.) The old “donut hole” coverage gap is gone. If your drug costs are high, this changes the math — a plan that gets you to the cap efficiently can be worth more than one with a lower premium. There's also a Medicare Prescription Payment Plan: it lets you spread your out-of-pocket drug costs across monthly payments over the year instead of paying a big bill all at once. It doesn't lower the total — it smooths the timing, which helps if a costly drug hits early in the year.

How to compare plans, step by step

1. Make your drug list first. Every medication, its dose, and how often you take it. (This is step two of the open enrollment checklist.)
2. Go to the Medicare Plan Finder at Medicare.gov — the official, unbiased comparison tool. Avoid insurance-company sites for the comparison; they only show their own plans.
3. Enter your drugs and your pharmacy. The Plan Finder uses both to estimate your real cost, because your pharmacy affects your copays.
4. Sort by total estimated yearly cost — not by premium. This column folds in premium, deductible, and your drug copays into one honest number.
5. Check that every drug is covered before you decide. Look for any medication flagged as not on the formulary or requiring prior authorization or step therapy.
6. Confirm your pharmacy is preferred under the plan you like, or check whether mail-order lowers your cost.

If you're also weighing whether to get drug coverage through a standalone Part D plan or bundled into a Medicare Advantage plan, our guide on Medicare Advantage vs. Medigap covers that structural choice. And for free one-on-one help, your State Health Insurance Assistance Program (SHIP) counselor can sit with you and run the Plan Finder together — no cost, no sales pitch.