Updated August 3, 2026. Quick answer: compare plans on your own drug list, not on premium. The premium is the smallest and most visible number; the formulary and the pharmacy network decide what you actually pay. And enrol on time even if you take nothing, because the late penalty is permanent.
The order to compare in
- Is every drug you take on the plan’s formulary? A drug that is not covered does not count toward the out-of-pocket cap and is not capped by it. This is the first filter and it eliminates most plans quickly.
- What tier is each drug on? Two plans can both cover a drug and charge very different amounts for it.
- Is your pharmacy in the preferred network? The same plan often charges different amounts at preferred and standard pharmacies.
- Are there restrictions? Prior authorisation, step therapy or quantity limits on your specific drugs.
- Then look at the premium and deductible.
Most people do this list backwards, and the reason is that the premium is the only figure presented up front while the rest requires entering your actual prescriptions.
Enrol on time even if you take no drugs
This is the most common expensive mistake at 65, and it is made by the healthiest people. The Part D late-enrolment penalty is added to your premium and it is permanent — what it costs over a retirement. A minimal plan you never claim on is cheap insurance against a penalty you would carry for life.
Re-check every year, even if nothing changed for you
Formularies, tiers and pharmacy networks change annually, and so does your plan’s own pricing. A plan that was right last year can be wrong this year without you doing anything. What to actually check each autumn.
Two costs that sit outside the plan
- IRMAA adds a surcharge to your Part D premium based on income from two years earlier, regardless of which plan you pick.
- The $2,100 out-of-pocket cap in 2026 applies to covered drugs under any plan.
General information drawn from Medicare, CMS and state insurance-department publications, not insurance advice. Medicare rules, plan availability and dollar figures change every year, and state rules differ. Every figure here is year-labelled and every source is named so you can check it against your own situation. We do not sell insurance and receive nothing if you buy a plan.
The window this happens in. A standalone drug plan can only be changed in the October window if you are in Original Medicare — the January window does not cover it: the two windows, side by side.