Open enrolment: what the 15 October window is actually for
Your plan is allowed to change its costs, its drug list and its doctors every January. Autumn is the only time most people can respond — and most don’t.
Here is the thing that makes Medicare different from almost every other product you buy.
Your plan can change its premium, its deductible, which drugs it covers, which tier each drug sits on, which pharmacies count as preferred, and which doctors are in network — every single January. You don't have to agree. You don't have to be consulted. You'll be told, in a letter, and if you do nothing you'll simply be enrolled in the new version.
Open enrolment is the window in which you're allowed to respond. Most people don't use it. Study after study finds that only a minority of enrollees compare plans in any given year, and a substantial number could have paid less by switching.
| 15 Oct – 7 Dec | Medicare Open Enrolment. Change Part D plans, switch between Original Medicare and Medicare Advantage, or move between Advantage plans. Changes take effect 1 January. |
|---|---|
| 1 Jan – 31 Mar | Medicare Advantage Open Enrolment. If you’re already in an Advantage plan, you get one switch — to a different Advantage plan or back to Original Medicare. |
| September | Your Annual Notice of Change arrives. This is the letter that matters. |
| All year | Special Enrolment Periods for qualifying events — moving, losing other coverage, your plan leaving your area, qualifying for Extra Help. |
The letter not to throw away
In September, your plan sends an Annual Notice of Change. It looks like every other piece of insurance mail, which is precisely the problem — it arrives in the same week as the marketing and gets treated as more of the same.
It is not marketing. It's a legally required document listing exactly what's changing about your plan in January. Premium, deductible, copays, drug list, network.
If you read one document this autumn, read that one. Compare it against what you're paying now. A great many people discover that the plan they've been happy with for years has quietly moved their main medication to a higher tier, or dropped their pharmacy from its preferred network.
Doing nothing is a decision. It re-enrols you in next year's version of a plan you chose based on this year's terms.
What actually changes year to year
- Formularies. Drugs move tiers, get dropped, or acquire new restrictions like prior authorisation or step therapy. This is the change most likely to cost you real money.
- Pharmacy networks. The same drug at the same plan can cost noticeably different amounts depending on whether your pharmacy is “preferred” or merely “in network.”
- Provider networks, if you're in Medicare Advantage. Doctors and hospitals leave networks, sometimes mid-year.
- Premiums and deductibles, including the Part D deductible, which can be up to $615 in 2026.
- Whole plans withdrawing from a county. If that happens you'll be notified and get a Special Enrolment Period — but you need to act.
How to do the review in about twenty minutes
The Plan Finder at medicare.gov does the arithmetic, and it's genuinely the best tool in government. Enter your actual prescriptions, doses and pharmacy, and it estimates your total annual cost per plan — premiums plus deductible plus copays — rather than the premium alone.
That distinction is the whole exercise. The lowest-premium plan is frequently not the cheapest plan for a specific person, and comparing premiums is how people end up paying hundreds more than they needed to.
- Read the Annual Notice of Change when it arrives in September. Check your own medications against the new drug list.
- Run the Plan Finder with your real prescriptions and your real pharmacy. Compare estimated annual totals.
- In Medicare Advantage? Confirm your doctors and hospital are still in network for next year. Don’t assume.
- Check whether your pharmacy is preferred under next year’s terms.
- Ask your SHIP counsellor for help if it’s confusing. Free, unbiased, and they earn nothing whichever plan you pick — unlike most people who will call you this autumn.
- Get it done before 7 December. The window doesn’t extend and it doesn’t care why you missed it.
Twenty minutes, once a year, in a window that's open for seven and a half weeks. It is genuinely one of the highest-return uses of time available to anyone on Medicare — and the main reason more people don't do it is that the mail arrives looking exactly like the mail they've learned to throw away.
This is general information, not personal advice. We report the rules, the numbers and the deadlines as clearly as we can. We don't know your income, your state, your health or your family — and all four can change the answer. Treat this as a good place to find the right questions, not a substitute for someone looking at your actual situation.
Where these facts come from
Checked against primary sources on 10 August 2026. Dollar limits and program rules change — if you're reading this well after that date, verify the numbers at the links below.
- Medicare — Joining a plan — https://www.medicare.gov/health-drug-plans/health-plans/your-coverage-options/joining-plan
- Medicare — Plan Finder — https://www.medicare.gov/plan-compare/
- Medicare — Drug coverage costs — https://www.medicare.gov/health-drug-plans/part-d/basics/costs
- SHIP — Free local Medicare counselling — https://www.shiphelp.org/
Edward Silva
Edward spent more than forty years as a computer professional — long enough to pick up one useful occupational habit: when somebody hands you a summary, go and read the actual documentation. He started The Second Half Guide after noticing that most writing aimed at people his age was either talking down to him or quietly selling him something, and that the plain facts — the dates, the thresholds, the dollar figures — were somehow the hardest part to find.
He's married, with two grown sons, both married themselves. He is not a financial adviser, an attorney or an insurance agent, and this site doesn't tell you what to do with your money. It tells you what the rules actually say, and links to where he checked.