How Medicare Part D Drug Tiers Work (2026)

If you're comparing Medicare Part D plans, or just wondering why a prescription cost more than you expected, the answer usually comes down to tiers. Your plan sorts every drug it covers into a cost tier, and that tier sets what you pay at the pharmacy. Once you know how Medicare Part D drug tiers work, the prices stop feeling random.

In This Guide

• Key Takeaways
• How Medicare Part D Drug Tiers Work
• What Each Part D Tier Usually Costs You
• Why the Same Drug Costs More on Another Plan
• How to Ask for a Lower Tier
• Frequently Asked Questions
• Learn More

How Medicare Part D Drug Tiers Work

Start with the formulary. Every Part D plan (whether it's a standalone drug plan or the drug coverage built into a Medicare Advantage plan) publishes a formulary, which is just the list of drugs that plan will pay for. If your drug isn't on the formulary at all, that's a different problem. Tiers are about the drugs that are covered.

Here's the piece that actually controls your cost. Many plans divide their formulary into cost-sharing tiers, and the tier a drug sits on determines your copay or coinsurance. According to Medicare's guide to how drug plans work, "generally, a drug in a lower tier will cost you less than a drug in a higher tier."1

So the tier isn't a quality rating or a medical judgment. It's a pricing bucket. A generic and a brand-name drug that treat the same condition can land on very different tiers, and you'll feel that difference every time you fill the prescription.

One quick vocabulary note, because it matters on the higher tiers. A copay is a flat dollar amount (say, the same fixed charge every time). Coinsurance is a percentage of the drug's price, so your cost rises with the price of the drug. When you look up a drug, check which of the two your plan charges on that drug's tier, because a percentage can climb with a pricey drug in a way a flat copay can't.

What Each Part D Tier Usually Costs You

Plans don't all use the same number of tiers or the same names, but a typical layout runs like this, from cheapest to priciest.1

Read that as a pattern, not a rulebook. Medicare's own example comes with the warning that your plan's tiers may be different, because each plan divides its tiers in its own way. The direction is what generally holds: a lower tier usually costs you less than a higher one, and the specialty tier at the top is where the very high-cost drugs live.1

The practical move is to look up your actual drugs on a plan's formulary and see which tier each one lands on before you enroll. That single step tells you more about what you'll really spend than the plan's premium does.

Why the Same Drug Costs More on Another Plan

This is the part that surprises people most, so it's worth being blunt about it. Each plan builds its own tiers and decides which drugs go on them. So the exact same drug can sit on Tier 2 in one plan and Tier 3 in another, and cost you a different amount in each.1

That's not a billing error. It's how the system is designed. Two plans with similar-looking premiums can leave you paying very different amounts once your specific medications are in the mix.

Which leads to the one rule that saves people the most money: compare plans on your drugs, not on the premium or the headline copays. Make a list of everything you take, including the dose, and check each drug against each plan's formulary. A plan with a slightly higher premium that puts your two daily medications on Tier 1 can easily beat a cheaper-sounding plan that files them on Tier 3. You can run that comparison in the Medicare Plan Finder at Medicare.gov.

How to Ask for a Lower Tier

Say your drug is stuck on a higher, pricier tier and there's no lower-tier alternative that works for you. You're not out of options. You or your prescriber can request a tiering exception, which asks the plan to charge you the cost-sharing of a lower, preferred tier for that drug.1

This isn't a favor the plan can simply ignore. Federal rules at 42 CFR 423.578 require every Part D plan that uses a tiered formulary to keep reasonable and complete procedures for handling these exception requests.1

Your prescriber has to back the request. They give the plan a supporting statement, by phone or in writing, saying that the preferred-tier drugs wouldn't work as well for you as the one you're asking about, would cause you adverse effects, or both. That statement is required, but it doesn't guarantee a yes: the plan approves the exception when it decides the drug you're requesting is medically necessary for your condition.1

There's one important limit. A plan is allowed to design its process so that drugs on its specialty tier can't be moved to a lower tier through a tiering exception.1 So ask your plan up front whether its process allows exceptions for specialty-tier drugs before you count on one.

Whatever the plan decides on your request, that decision counts as a formal coverage determination.1 If the answer is no, our guide to asking your drug plan to cover a denied drug walks through what to do next.

Learn More

Find personalized help comparing Medicare Part D plans on your own drug list at brevy.com.

The information on Brevy.com is for educational purposes only and is not a substitute for professional legal, financial, or medical advice. Rules vary by state and program and change frequently. Always verify with the relevant agency or a qualified professional. Brevy is not a law firm, financial advisor, or healthcare provider.