How to Compare Medicare Part D Formularies in 2026
August 12, 2026
Why Comparing Part D Formularies Matters
A Medicare Part D formulary comparison tells you whether a plan covers your specific medications, what tier each drug sits on, and roughly what you'll pay for it before the plan year even starts. A formulary is the official list of prescription drugs a Medicare Part D plan has agreed to cover, and it's organized into cost-sharing tiers that determine your copay or coinsurance. Every stand-alone Part D plan and every Medicare Advantage plan that includes drug coverage publishes its own formulary, and no two are identical, even plans from the same insurer can cover different drugs at different tiers. That's why comparing formularies, not just premiums, is one of the most important steps when you're choosing or reviewing Medicare drug coverage.
Quick Answer
To compare Medicare Part D formularies, list your current prescriptions with dosages, then check each plan's covered drug list for whether your medications are included, which tier they're on, and whether restrictions like prior authorization or quantity limits apply. Use Medicare's Plan Finder tool to run this comparison for multiple plans at once, and repeat the check every fall since formularies can change from one plan year to the next.
How Part D Formulary Tiers Work
Most Part D formularies group covered drugs into tiers, and the tier a drug sits on drives what you pay at the pharmacy. A tier is a cost-sharing category a plan assigns to a drug, generally based on whether it's generic, brand-name, or specialty. According to Medicare.gov, plans typically use a five-tier structure, with lower tiers costing you less and higher tiers, especially specialty drugs, costing significantly more.
The exact tier names, drug placements, and copay amounts vary by plan, so a medication on Tier 2 with one insurer might sit on Tier 3 with another. This is the core reason a side-by-side compare medicare plans review matters: the plan with the lowest premium isn't automatically the plan with the lowest total cost for your specific drug list.
Formulary Basics at a Glance
Typical Part D Formulary Tier Structure
| Feature | What It Typically Includes | Typical Cost-Sharing |
|---|---|---|
| Tier 1 | Preferred generic drugs | Lowest copay |
| Tier 2 | Generic drugs | Low copay, slightly above Tier 1 |
| Tier 3 | Preferred brand-name drugs | Moderate copay |
| Tier 4 | Non-preferred drugs (generic or brand) | Higher copay or coinsurance |
| Tier 5 | Specialty drugs | Highest coinsurance percentage of any tier |
Formulary Restrictions That Affect Your Cost
Beyond tier placement, a formulary can attach rules to specific drugs that affect whether, and how, a plan covers them. Three restrictions show up most often:
- Prior authorization requires your prescriber to get plan approval before the drug is covered.
- Step therapy requires you to try a lower-cost drug first and show it doesn't work before the plan covers a more expensive alternative.
- Quantity limits cap how much of a drug the plan will cover in a given time period, such as a 30-day supply.
These restrictions can apply even when a drug technically appears on the formulary, so checking tier placement alone isn't enough, you also need to see whether any of these flags are attached to your specific medications. A plan's medicare star ratings can offer a rough sense of member satisfaction and plan quality, but they won't tell you whether your prescriptions carry these restrictions, so a direct formulary check is still necessary.
How to Compare Part D Formularies Step by Step
List every medication you take
Write down each drug's exact name, dosage, and how often you fill it, including any specialty or brand-name prescriptions.
Pull each plan's formulary
Check the plan's published drug list, either through the insurer's website or Medicare's Plan Finder tool.
Confirm each drug is covered
Search for every medication by name to see if it appears on the formulary at all, not every plan covers every drug.
Check the tier and estimated cost
Note which tier each drug falls under and the estimated copay or coinsurance shown for that plan.
Look for restrictions
Check whether prior authorization, step therapy, or quantity limits apply to any of your medications.
Repeat the check every fall
Formularies can change each plan year, so re-run this comparison during Medicare's Fall Open Enrollment period.
Pharmacy Network and Total Cost
Your out-of-pocket cost depends on more than the formulary tier, it also depends on which pharmacy you use. Part D plans contract with preferred and standard network pharmacies, and preferred pharmacies typically offer lower copays for the same drug at the same tier. Filling a prescription outside your plan's network, or at a standard rather than preferred pharmacy, can raise your cost even when the drug and tier stay the same.
Formulary comparison also connects directly to your annual drug spending. Once your total drug costs reach a certain point, you move into the medicare part d coverage gap donut hole explained phase, where cost-sharing rules shift again. Comparing formularies before you enroll helps you estimate how quickly you'd move through these phases based on the drugs you actually take.
Advantages of Comparing Formularies Every Year
- Helps you catch cost increases or coverage drops before they affect your pharmacy visit
- Lets you estimate your full-year drug costs, not just the monthly premium
- Reveals whether a lower-premium plan actually costs more once your specific drugs are factored in
- Gives you a documented basis for switching plans during enrollment periods
Considerations
- Formularies can run dozens of pages, so checking every medication takes time
- Tier names and structures aren't standardized across insurers, making direct comparison harder
- Plans can add restrictions like prior authorization mid-year with notice, so your comparison isn't permanent
- Specialty drug costs can be difficult to estimate precisely without contacting the plan
Formulary Comparison Checklist
- List all current prescriptions with exact names and dosages
- Confirm each drug appears on the plan's formulary
- Note the tier and estimated cost for each drug
- Check for prior authorization, step therapy, or quantity limits
- Confirm your preferred pharmacy is in the plan's network
- Re-check the formulary each year during Fall Open Enrollment
Formularies Can Change Annually
Part D formularies can change from one plan year to the next, and plans can also adjust formularies during the year in limited circumstances. According to CMS, plans must notify affected enrollees in advance when they remove a covered drug or move it to a higher cost-sharing tier. Recheck your formulary every year during Medicare's Fall Open Enrollment period (October 15, December 7) even if you're happy with your current plan.
Tools That Make Comparison Easier
Medicare's Plan Finder tool lets you enter your medications, dosages, and pharmacy preference, then compares estimated annual costs across every Part D and Medicare Advantage drug plan available in your area. This is generally the fastest way to run a formulary comparison without reading each plan's full drug list manually. If your income and resources are limited, the Social Security Administration's Extra Help program can lower your Part D premiums, deductible, and copays, which is worth checking before you assume a plan is unaffordable based on formulary costs alone.
If you're weighing Medicare Advantage against Original Medicare paired with a stand-alone Part D plan and a Medicare Supplement policy, remember that formulary comparison applies to the drug coverage piece either way, a Medigap policy like medicare supplement plan n doesn't include drug coverage on its own, so you'd still need to compare Part D formularies separately. If you're considering a change in coverage typeswitching from medicare advantage to medigap involves its own timing rules worth reviewing alongside your drug plan comparison.
Missing enrollment deadlines when you first become eligible can also affect your future drug costs. Reviewing the late enrollment penalty rules is worth doing alongside your formulary comparison if you're newly eligible for Medicare.
Related Guides
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Frequently Asked Questions
The formulary is the full list of drugs a plan covers. A tier is the cost-sharing category within that formulary that determines your copay or coinsurance for a specific drug, lower tiers generally cost less than higher tiers.
Plans generally aren't supposed to remove a covered drug or raise its cost-sharing during the plan year except in limited circumstances, such as a drug being pulled from the market or a generic becoming available. When a change does happen, plans are required to notify affected enrollees in advance.
Yes. Medicare Advantage plans that include drug coverage (MA-PD plans) each publish their own formulary, and it can differ from the formularies used by stand-alone Part D plans, even from the same insurer.
Compare formularies at least once a year, ideally during Medicare's Fall Open Enrollment period from October 15 through December 7, since plans can change covered drugs, tiers, and restrictions for the upcoming plan year.
Each plan publishes its formulary on its own website, and you can also search covered drugs across multiple plans at once using Medicare's Plan Finder tool at Medicare.gov.