The most common thing people do during Medicare Open Enrollment is nothing, and that is a decision rather than the absence of one.
Doing nothing does not keep your coverage the same. It rolls you into next year's version of your plan, at next year's price, with next year's network and next year's drug list. Whether that is fine or expensive depends entirely on what your plan has decided to do in January — and it has already decided.
The dates
Open Enrollment happens from October 15 to December 7.
Changes you make are effective January 1 of the following year, and the plan must receive your enrollment request by 7 December. That is a receipt deadline, not a postmark deadline, which is a distinction worth respecting in the final week.
What you are allowed to change
Medicare is specific about the moves available in this window:
- Join, drop, or switch to another Medicare Advantage plan, with or without drug coverage
- Join, drop, or switch to another Medicare drug plan if you are in Original Medicare
- Switch between Original Medicare and a Medicare Advantage plan in either direction
That last one is the largest decision available to most people, and the one least suited to being made in the first week of December. Original Medicare and Medicare Advantage are different products with different economics — most importantly, Original Medicare has no annual cap on what cost sharing can total, which is the structural gap covered in the guide to what Medicare actually costs.
What your plan is allowed to change
This is the part that makes the window matter even for people with no complaints.
Medicare health and drug plans can make changes each year — cost, coverage, and which providers and pharmacies are in their networks.
So four things can move under a plan name that stays identical:
- The premium and deductible.
- The provider network. A doctor in network this year may not be next year.
- The pharmacy network, which is a separate list from the drug list and is regularly overlooked.
- The formulary — which drugs are covered, at what tier, and with what prior-authorisation requirement.
A prescription that costs a few dollars a month can move tier and become a genuinely different number. Nobody is notified of this at the pharmacy counter in January; they are notified in the autumn, by post.
The one document worth opening
Your plan sends an Annual Notice of Change describing what is changing for the coming year.
It is dull, it arrives among a great deal of marketing from insurers who would like you to switch, and it is the only piece of paper in the pile that tells you what is actually happening to the coverage you already have. Open that one. The changes it describes take effect whether or not it is read.
What Open Enrollment does not touch
Two things people reasonably expect to be in scope are not.
Your Part B premium. The standard premium is set nationally; no plan choice changes it.
Your income-related surcharge, if you pay one. That is determined by Social Security from the income on your tax return two years earlier, and it is a cliff rather than a slope — one dollar over a threshold triggers the whole step. How those brackets work, and the appeal available after a life-changing event such as retirement, is set out in the IRMAA guide.
How to use the window without losing a weekend to it
A full comparison of every plan available to you is a large job and mostly unnecessary. A shorter version catches most of the value:
- Read the Annual Notice of Change. If nothing material moved, you may be done.
- List your current prescriptions and check each against next year's formulary for your plan.
- Check your doctors are still in network for next year, not just this year.
- If you are in Original Medicare, consider whether your supplemental arrangement still fits, because the absence of an out-of-pocket cap is what that cover exists to address.
- Diary 7 December, and aim to be finished a week before it.
This article sets out the enrollment rules published by Medicare and CMS. It is not insurance or financial advice, and the right plan depends on your health, your prescriptions, your doctors and your budget. Compare plans on Medicare.gov or call 1-800-MEDICARE, and consider free counselling from your State Health Insurance Assistance Program.
Sources
- Medicare.gov — Open Enrollment (opens in a new tab)
- CMS — Medicare Open Enrollment partner resources (opens in a new tab)
- Medicare.gov — Your Yearly Medicare Review (opens in a new tab)
- Medicare.gov — Understanding Medicare Advantage and Medicare drug plan enrollment periods (opens in a new tab)
- Medicare.gov — Remember key Medicare dates (opens in a new tab)
This article is general information for a United States audience and reflects enrollment rules published by Medicare and CMS at the date of review. It is not insurance, tax or financial advice. Plan terms, networks and formularies vary and change annually, and only your plan documents govern your coverage. Compare plans on Medicare.gov and consider free counselling from your State Health Insurance Assistance Program before deciding. Last reviewed 15 September 2026.
