Part D and your prescriptions

Prescription coverage is the part of Medicare people most often set and forget. It's also the part that most reliably rewards a yearly look.

How a drug plan actually works

Each plan publishes a formulary — the list of medications it covers — and sorts them into tiers. Lower tiers cost you less; higher tiers cost you more. Two plans can cover exactly the same medication and put it in different tiers.

Plans can also require steps before they'll pay: trying a cheaper alternative first, getting approval in advance, or limiting the quantity. None of these are unusual, and none of them are hidden — but you only find them by looking at your own medications against a specific plan.

Why "which one costs least" is the wrong question

There's no such thing in the abstract. There's only what a plan costs for your list of medications, at your pharmacy, this year.

Someone taking nothing and someone taking four maintenance medications should almost certainly not be in the same plan. The comparison only means anything once your actual prescriptions are in it.

The yearly check that's worth doing

Plans change their formularies, their tiers, and their costs every year. So does your prescription list, sometimes.

Between October 15 and December 7 you can change your drug plan for the year ahead. Nothing about your health has to have changed for it to be worth looking — the plan can change underneath you while you stay exactly the same.

This is the single most common place I find people money, and it costs nothing to check.

If you take no medications at all

It still usually makes sense to have a drug plan.

Going without creditable prescription coverage after your enrollment window closes adds a permanent amount to what you pay later, calculated from how many months you went without. It isn't for this year. It's insurance against the penalty and against a diagnosis you can't schedule.

More on that in the enrollment windows.

Where drug coverage comes from

It depends which path you're on:

• On Original Medicare, you buy a standalone Part D plan.
• On Medicare Advantage, drug coverage is usually built into the plan.

That difference is one of the things worth weighing in the two paths.