How to check your prescriptions against a Part D formulary

Part D plans are marketed on their monthly premium because it is the one number that is easy to compare. It is also close to irrelevant. What determines your real annual cost is whether each of your medications appears on that plan's formulary, which tier it sits on, and whether the plan requires extra steps before it will pay.

Build the list first

Before you look at a single plan, write down every prescription you take. For each one, record the exact name, the dosage in milligrams, how many you take per day, and whether you fill a 30-day or 90-day supply. Generic and brand versions are treated as different drugs, so note which one you actually take.

If you use a mail-order pharmacy or a specific local pharmacy, write that down too. Plans have preferred pharmacies where your copay is lower, and the difference on a maintenance medication over a year can be a few hundred dollars.

What to look for in the formulary

A formulary is the plan's list of covered drugs, organized into tiers. Tier 1 is usually preferred generics with the lowest copay; the top tiers are specialty drugs where you may pay a percentage of the cost rather than a flat amount. Three restrictions matter as much as the tier:

• Prior authorization — your doctor has to justify the prescription before the plan pays. Expect delays at the pharmacy counter.
• Step therapy — the plan requires you to try a cheaper drug first and document that it did not work.
• Quantity limits — the plan caps how much it will cover in a given period, which matters for medications taken more than once a day.

Run the numbers on Medicare's own tool

The Medicare Plan Finder at Medicare.gov lets you enter your drug list and your pharmacy, then shows estimated total annual cost — premium plus deductible plus copays — for every plan available in your ZIP code. Sort by that total, not by premium. It is common for the plan with the fourth or fifth lowest premium to be several hundred dollars cheaper across the year.

Formularies change every January. A plan that covered your medication on tier 2 this year can move it to tier 3, add prior authorization, or drop it entirely — and the only notice you get is a letter in the fall that is easy to mistake for junk mail.

Re-check every autumn

The Annual Notice of Change arrives each September. It lists exactly what is changing about your plan for the coming year. Fifteen minutes with that letter and the Plan Finder is the highest-return task in the whole Medicare calendar, and it is the one most people skip.

If reading formulary tables is not how you want to spend an evening, that is a fair thing to hand off. It is most of what we do each October and November.

This article is general education and is not advice about your individual situation. Plan availability, costs and formularies change annually and vary by county. We do not offer every plan available in your area. Any information we provide is limited to those plans we do offer in your area. Please contact Medicare.gov, 1-800-MEDICARE, or your local State Health Insurance Assistance Program to get information on all of your options.