Medicare’s fall enrollment window opens October 15 and closes December 7, 2026. Whatever you choose during those eight weeks takes effect January 1, 2027 — which is the first thing worth getting straight, because the naming causes real confusion. The enrollment period happening in late 2026 sets your 2027 coverage. If you are comparing plan documents this fall, you are shopping for next year.
For women, the stakes on this particular decision compound in ways they do not for men, and one of the choices available in October is close to irreversible. It is worth understanding which one before the window opens.
Two Different Things Are Called Open Enrollment
This trips up a lot of people, including people who have been on Medicare for years.
The Annual Enrollment Period (October 15 – December 7) is the broad one. During it you can switch Medicare Advantage plans, change or drop your Part D drug plan, move from Original Medicare to Medicare Advantage, or move from Medicare Advantage back to Original Medicare.
The Medicare Advantage Open Enrollment Period (January 1 – March 31) is narrower. If you are already in a Medicare Advantage plan, it gives you one opportunity to switch to a different Advantage plan or drop back to Original Medicare. It does not let someone on Original Medicare join an Advantage plan, and it does not give you a standalone Part D shopping window.
If a plan sends you a non-renewal notice — and market consolidation has produced a steady stream of these as insurers exit unprofitable Advantage markets — you qualify for a Special Enrollment Period and must select new coverage before your existing plan ends. Do not wait for the general window if you receive one of those letters.
What Part D Actually Costs Now
The Inflation Reduction Act restructured the Part D drug benefit, and the structure is worth knowing because it changed what “catastrophic” coverage means for household budgeting.
For 2026, the standard Part D design works like this: you pay the full cost of covered drugs until you meet a $615 deductible, then 25% coinsurance during the initial coverage phase, until your out-of-pocket spending on covered Part D drugs reaches $2,100. Above that threshold, you pay nothing for covered Part D drugs for the rest of the year.
That hard cap is the meaningful change. Before the IRA, Part D had no true out-of-pocket ceiling, which meant a single expensive specialty drug could produce unbounded annual costs. Now there is a number, and it is a number you can plan around.
For 2027, CMS is codifying these IRA changes in regulation rather than operating them through annual program instructions, because that instruction authority expires — the relevant rule was published in the Federal Register on April 6, 2026. The codified structure eliminates the old coverage gap phase, removes cost sharing in the catastrophic phase, and incorporates the Manufacturer Discount Program. The 2027 out-of-pocket threshold is indexed upward from the 2026 figure; rather than rely on a projection, read the actual number off your plan’s Annual Notice of Change, which arrives by the end of September. That document is the authoritative statement of what your specific plan will charge you next year, and it is the single most useful piece of mail you will get this fall.
The Medigap Trap Is the Decision That Matters Most
Here is the asymmetry that deserves more attention than it gets.
When you first become eligible for Medicare, you have a one-time window during which you can buy a Medigap (Medicare Supplement) policy on a guaranteed-issue basis — the insurer must sell to you and cannot price you on your health history. If you choose Medicare Advantage instead and later decide you would rather have Original Medicare plus Medigap, that guaranteed-issue protection is generally gone in most states. The Medigap insurer can require medical underwriting, and it can decline you or charge more based on conditions you have developed in the meantime.
The practical effect is that the Advantage-versus-Original decision is much easier to make in one direction than the other. You can move from Advantage back to Original Medicare during the annual window — that part is straightforward — but you may not be able to buy the supplemental coverage that makes Original Medicare financially predictable.
This matters disproportionately for women for a mechanical reason: the longer you live, the more likely you are to accumulate exactly the conditions that make underwriting go badly. A woman evaluating this at 65 in good health is making a decision whose consequences land at 78, when her health history is no longer a blank page. A few states require guaranteed issue or annual open enrollment for Medigap regardless of health; most do not. Find out which category your state is in before you treat the choice as reversible.
What Longevity Does to the Math
Women’s longer average lifespans change several inputs at once.
More years on Medicare means more years of premiums, more years of drug costs, and a higher likelihood of needing the sustained specialty medication that makes the Part D cap valuable rather than theoretical. It also means a longer period of exposure to Medicare Advantage networks — and network adequacy is the part of an Advantage plan most likely to change year over year. A plan that includes your cardiologist today may not next year, and the provider directory is worth checking against your actual doctors annually rather than assuming continuity.
Widowhood introduces a timing quirk worth planning around. Medicare’s income-related monthly adjustment amount — the surcharge higher-income beneficiaries pay on Parts B and D — is based on your tax return from two years prior. A woman whose household income drops sharply after her husband’s death can find herself paying a surcharge calculated on joint income she no longer has. This is fixable: Social Security accepts a request for reconsideration when a life-changing event such as the death of a spouse has reduced income, using form SSA-44. Very few people know to file it.
What to Do This Fall
Wait for your Annual Notice of Change in late September, then read three things in it: the new premium, the new out-of-pocket maximum, and whether your specific prescriptions are still on the formulary at the same tier. Formulary tier changes are the most common way a plan gets more expensive without the premium moving at all.
Then check your doctors against the plan’s current directory rather than last year’s. And if you are approaching 65 and deciding between Advantage and Original Medicare for the first time, treat the Medigap underwriting question as the central issue rather than a footnote — it is the one part of this decision that does not stay open.
