The best way to compare Medicare Part D plans is to match each plan to the prescriptions you actually take, the pharmacies you use, and the total costs you expect over the year.
What to compare first
| What to check | Why it matters |
|---|---|
| Formulary | Each plan has its own covered-drug list, so one plan may cover your drug differently from another. |
| Premium | This is your monthly cost for the plan, even if you do not fill a prescription. |
| Deductible | Some plans make you pay part of your drug costs before regular coverage begins. |
| Copays and coinsurance | These affect what you pay when you fill covered prescriptions. |
| Pharmacy network | Preferred in-network pharmacies may lower your out-of-pocket costs. |
| Plan rules | Prior authorization, step therapy, and quantity limits can affect access and cost. |
Know your two main Part D options
| Option | What it does | Who can join |
|---|---|---|
| Separate Medicare drug plan | Adds Part D coverage to Original Medicare and some other Medicare plan types | You must have Part A and/or Part B. |
| Medicare Advantage plan with drug coverage | Bundles Part A, Part B, and usually Part D in one plan | You must have both Part A and Part B. |
If you already have Medicare Advantage, check whether your plan already includes drug coverage before trying to add a separate Part D plan. In many cases, adding a separate drug plan is not allowed and can change your other coverage.
How to compare a plan’s drug coverage
Start with a written list of your prescriptions. Then review each plan’s formulary to see whether your drugs are covered, what tier they are on, and whether the plan applies restrictions. Lower tiers often mean lower cost sharing, but each plan builds its tiers differently.
If a needed prescription is not on the formulary, ask your prescriber and the plan about the exception process or covered options. Do not change treatment based on an insurance article.
Why pharmacies matter
Two plans can look similar until you compare pharmacy pricing. Check whether your regular pharmacy is in network, whether the plan has preferred in-network pharmacies, and whether mail order is available for ongoing prescriptions. Out-of-network fills can cost more, and you may have to pay full cost up front before asking the plan whether any refund applies.
Plan rules that can affect access
Part D plans may use prior authorization, step therapy, and quantity limits. These are not the same thing:
- Prior authorization: the plan requires approval before covering certain drugs.
- Step therapy: the plan may require trying a lower-cost option first.
- Quantity limits: the plan limits how much of a drug it covers over a set period.
When your drug coverage begins, you may also receive a transition fill for a drug you have been taking that is not covered or now has a new utilization rule. That transition fill is a member protection offered by the plan at the start of coverage.
Do not ignore late-enrollment risk
If you delay Part D and go 63 consecutive days or more without Medicare drug coverage or other creditable prescription drug coverage, you may owe a late-enrollment penalty if you join later. That is one reason to compare plans when you are first eligible, even if you do not currently take many prescriptions.
Quick comparison checklist
- Make a complete list of your prescriptions.
- Check each plan’s formulary.
- Review tiers and cost sharing.
- Confirm your pharmacies are in network.
- Check for preferred pharmacy pricing or mail order.
- Look for prior authorization, step therapy, or quantity limits.
- Consider whether you have creditable drug coverage already.
People who qualify for Extra Help do not pay the Part D late-enrollment penalty. Confirm existing creditable coverage before canceling it; changing coverage can affect employer or union benefits.
Related coverage questions
- Medicare Part D: Coverage Choices, Enrollment and Costs
- Medicare Part D Costs: Premiums, Deductibles and Annual Limits
- Creditable Coverage: Part D Notices and Part B Enrollment Rules