Summary: The right Part D plan is the one with the lowest total annual cost for your specific drugs at your preferred pharmacy: premium plus deductible plus copays. Premiums range from under $10 to over $100 a month, but the cheapest premium rarely wins on total cost. This guide gives you a repeatable open-enrollment process: check the formulary, price your drugs, compare pharmacy options, and use star ratings as the tiebreaker.
Every fall, from October 15 to December 7, you can change Part D plans for the following year. Most beneficiaries do not, and most beneficiaries overpay. Plans change their formularies, premiums, and pharmacy networks annually, so last year's right answer is this year's guess.
The process below takes about an hour with Medicare's plan finder and your medication list. It is the highest-value hour in the Medicare calendar.
Every September, your current plan mails an Annual Notice of Change listing next year's premium, formulary changes, and tier changes. Read it before you run the plan finder, because it tells you what is changing about the plan you already have. A drug moving from tier 2 to tier 3, or a premium rising $20 a month, can flip the ranking.
The notice also flags service-area and pharmacy network changes. If your preferred pharmacy leaves the preferred network, your costs rise even though the plan name is identical. Ten minutes with the notice plus an hour with the plan finder is the complete annual process, and skipping either half is how beneficiaries overpay.
Write down every prescription: exact drug name, dosage, frequency, and whether you use brand or generic. The plan finder prices specific drugs, not conditions; 'blood pressure medication' is not an input. Include drugs you take intermittently and any you expect to start, like a planned new prescription your doctor mentioned.
Note your preferred pharmacy too, or whether you prefer mail order. Pharmacy pricing varies within the same plan, and the plan finder lets you compare retail versus mail-order totals.
Before comparing prices, confirm each plan covers your drugs. A plan that does not cover your most expensive medication is disqualified no matter how cheap its premium is, because non-covered drugs sit outside the $2,100 out-of-pocket cap entirely. Formularies change every year: a drug covered this year may move to a higher tier or require prior authorization next year.
Pay special attention to utilization rules: prior authorization, step therapy, and quantity limits. A covered drug with a step-therapy requirement you cannot satisfy is effectively uncovered until you fight the appeal.
Medicare's plan finder computes estimated total annual cost: twelve months of premium plus your drug cost-sharing at your pharmacy. This is the only number that matters. A $15 premium plan with high tier copays routinely loses to a $40 premium plan with low copays for beneficiaries taking brand drugs.
Run the finder twice: once for your regular retail pharmacy and once for mail order or the plan's preferred pharmacy. The pharmacy switch alone can save hundreds a year, and it is free to choose at enrollment.
When two plans price within a couple hundred dollars of each other, star ratings decide. CMS rates plans 1 to 5 stars on drug pricing accuracy, customer service, and member experience. Plans with 5 stars can be joined outside open enrollment, a useful escape hatch.
Do not over-weight stars against big cost differences. A 5-star plan that costs $800 more a year than a 3.5-star plan is not the better deal for most people. Stars measure experience quality, and experience quality is worth something, just not $800.
If your income and assets are limited, the Low-Income Subsidy (Extra Help) can cut Part D premiums, deductibles, and copays to near zero. Many eligible beneficiaries never apply. The Social Security Administration's screening takes minutes, and qualifying changes the entire plan math: with Extra Help, the premium differences that dominate standard shopping nearly vanish.
Even if you assume you earn too much, check. The asset limits exclude your home and car, and the income thresholds surprise people.
Put a recurring calendar reminder for mid-October: export your drug list, run the plan finder, and switch if the math says so. Plans count on inertia; the beneficiaries who switch when it pays are effectively subsidized by the ones who do not. An hour a year is the cheapest insurance in the program.
Bring a helper if the plan finder feels overwhelming: State Health Insurance Assistance Programs (SHIPs) offer free, unbiased Medicare counseling in every state, and their counselors do this exact comparison all day during open enrollment. There is no reason to pay an agent for advice that a free public counselor gives without a sales agenda. Book early in the enrollment window; appointments fill up by November. If your drugs changed mid-year, do a quick mid-year check too: you cannot switch plans until open enrollment, but knowing next year's ranking early lets you act on day one.
October 15 to December 7 each year, for coverage starting January 1. This is when you can join, switch, or drop Part D and Medicare Advantage plans.
Rarely. Compare estimated total annual cost (premium + drug cost-sharing) for your specific drugs at your pharmacy. Cheap premiums often pair with expensive tier copays.
CMS 1-to-5-star quality ratings covering pricing accuracy, customer service, and member experience. Use them as a tiebreaker between similarly priced plans.
The Low-Income Subsidy: premium, deductible, and copay assistance for beneficiaries with limited income and assets. Apply through the Social Security Administration.
Open enrollment dates per CMS. This guide is for planning only.