Prescription Drug Cost Optimization

Why is the cheapest drug plan this year almost never the cheapest one next year? Because Part D plans rewrite their formularies and pricing every January, and the one you picked is betting you won’t notice. Most retirees don’t, and they overpay for years.

Prescription coverage is the corner of Medicare people set once and forget. That’s exactly backward. Of all the Medicare decisions, Part D is the one built to be redone annually, and the savings from doing it are larger than almost anything else on a healthy retiree’s healthcare bill.

How Part D actually prices you

Part D is private drug coverage, sold standalone alongside Original Medicare or bundled into a Medicare Advantage plan. Three things determine what you pay, and only one is the premium:

• The premium, the monthly cost of the plan itself.
• The formulary, the plan’s list of covered drugs and which tier each sits on. A drug on a low tier costs you little. The same drug on a high tier, or off the list, costs a lot.
• The pharmacy network, because plans now have preferred pharmacies where your copay is lower.

A plan with a low premium can be the most expensive option for you if your specific medications land on bad tiers. The premium is the headline. The formulary is the bill.

The 2026 redesign worth understanding

Part D went through a major redesign, and the headline matters: there’s now a hard annual cap on what you pay out of pocket for covered drugs, after which your costs for the year stop. The old coverage gap, the “donut hole” that exposed people to a painful middle stretch, is gone.

That cap changes the calculus for anyone on expensive specialty drugs. It means a serious prescription no longer runs without a ceiling, and the year-end exposure that used to blindside people is bounded. It also means the smart move for high-cost-drug users is checking whether a plan’s formulary covers their medication at all, because the cap only helps on covered drugs.

There’s also a program to spread your drug costs into level monthly payments across the year rather than front-loading them. For a retiree managing cash flow, that smoothing can be worth setting up.

The annual move that pays

Here’s the discipline almost nobody keeps. During open enrollment each fall, you re-shop Part D against your actual current medications. Plans change their formularies and pricing for the coming year, and your prescription list changes too. The plan that won last year can lose badly this year for reasons that have nothing to do with you.

The tool that does this is free and underused: Medicare’s Plan Finder lets you enter your exact drugs and doses and ranks plans by your total annual cost, premium plus copays, not just premium. Run it every year. I’ve seen the difference between a re-shopped plan and a forgotten one run to four figures annually, year after year, which compounds into real money over a retirement. The mechanics are also covered in prescription drug plan selection.

The IRMAA surcharge on top

If your income is high, Part D carries the same income surcharge as Part B. The Part D IRMAA ranges from $14.50 a month at the first tier to $91.00 at the top in 2026, added on top of whatever your plan charges, and priced off your income from two years ago. So a Roth conversion or a big gain doesn’t just raise your Part B premium, it raises your drug premium too. Managing the income that triggers it is the same exercise as the rest of IRMAA and MAGI planning.

If a medication isn’t covered well

When a drug you need sits on a bad tier or off the formulary, you have moves before you just pay:

• Compare on total cost, not premium, using your real drug list every fall.
• Use preferred pharmacies, including mail-order for maintenance medications, where copays are lower.
• Ask about therapeutic alternatives. A clinically equivalent drug on a better tier can cut the cost sharply, a conversation for you and your physician.
• Check the manufacturer and assistance programs for high-cost specialty drugs.
• If your income is modest, the Extra Help program can slash Part D costs, though it phases out well below a high-net-worth income.

Part D rewards the one habit most retirees skip: re-shopping once a year against the drugs you actually take. The plan is counting on your inertia. Beat the inertia and the savings show up every January, which over twenty Januarys is a number worth an afternoon of your attention.