Retirees Get About Eight Weeks Every Fall to Fix a Medicare Mistake. Most Let Open Enrollment Pass Without Checking a Thing.

Retirees Get About Eight Weeks Every Fall to Fix a Medicare Mistake. Most Let Open Enrollment Pass Without Checking a Thing.

David Beren

Sun, September 6, 2026 at 4:07 PM GMT+3 6 min read

Quick Read

• Medicare's Annual Enrollment Period runs October 15 through December 7, and most retirees skip the review, letting plans auto-renew into potentially costlier coverage.

• Beneficiaries should run prescriptions through Medicare.gov's Plan Finder every year, since a single drug moving from tier 2 to tier 4 can add hundreds in costs.

• Switching from Medicare Advantage back to Original Medicare is rarely reversible, since Medigap insurers can deny or surcharge applicants with health conditions developed while on Advantage.

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The Medicare Annual Enrollment Period is the one stretch of the calendar when almost every retiree can change almost every part of their coverage. It runs from October 15 through December 7 every year, which is roughly eight weeks. During that window, any Medicare beneficiary can switch Part D drug plans, move between Original Medicare and Medicare Advantage, or change Advantage plans.

Miss it, and the next chance to switch generally does not come around for another full year. Yet industry surveys have long shown that only a small minority of beneficiaries actively compare plans before letting their coverage auto-renew. The story here is inertia, and the cost of inertia is real money.

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What Annual Enrollment Actually Covers

Medicare has several enrollment windows, and mixing them up is the single most common coverage mistake. The fall Annual Enrollment Period lets anyone with Medicare change Part D or Advantage coverage. It is different from the Medicare Advantage Open Enrollment Period in the first quarter of the year, which is narrower and only for people already in an Advantage plan. It is also separate from the Initial Enrollment Period tied to turning 65, the General Enrollment Period for people who missed their initial sign-up, and the one-time Medigap open enrollment window that follows Part B enrollment. That Medigap window is the longest-lasting decision of them all, because it is the only guaranteed period to buy a supplement without medical underwriting, meaning insurers can otherwise reject applicants or charge more based on health.

Read the Annual Notice of Change First

Every fall, before the enrollment window swings open, all Part D and Medicare Advantage plans are required to mail out an Annual Notice of Change. It is arguably the most important piece of mail a retiree will receive all year, and most people toss it in the trash without a second thought. That notice spells out exactly what your plan will look like in the coming year, including the new premium, deductible, formulary changes, tier adjustments, and any shifts in preferred pharmacy networks. A plan that was the most affordable option last year is often not the most affordable this year, because insurers revise these terms annually. Doing nothing means you get auto-renewed into whatever the plan has become.

Re-Check the Part D Drug Plan Every Single Year

The most expensive failure during Annual Enrollment is not re-running the Part D comparison on Medicare.gov's Plan Finder. Even if a retiree's prescriptions have not changed, the plans have. A drug moved from tier 2 to tier 4, or dropped from the formulary entirely, can add hundreds of dollars in out-of-pocket costs. The Plan Finder lets beneficiaries enter their actual medication list and preferred pharmacy and see the total projected annual cost by plan. Run it every year, without exception. And the Part D late enrollment penalty for going without creditable drug coverage is permanent, added to the premium for as long as the beneficiary has Part D.

Medigap Trap Hiding Inside Advantage

Switching from Medicare Advantage back to Original Medicare during the fall window sounds reversible. It often is not. Once outside a guaranteed-issue period, Medigap supplement insurers in most states can medically underwrite, meaning they can decline the applicant or price the policy based on health history. A retiree who developed a serious condition while on Advantage may find that they cannot buy a supplement to pair with Original Medicare at any reasonable price. That makes the Advantage-to-Original switch far less reversible than the enrollment window implies.

2026 Premiums That Make This Decision Matter

The stakes for getting this decision right are rising quickly. The standard Medicare Part B premium is $202.90 per month in 2026, up from $185.00 in 2025, and the Part B deductible is $283, up from $257. The Part A hospital deductible climbed to $1,736 per benefit period. Higher-income beneficiaries pay income-related monthly adjustment amounts on top: individuals with modified adjusted gross income above $109,000, or joint filers above $218,000, pay a surcharge on both Part B and Part D. Meanwhile, the 2027 Social Security cost-of-living adjustment is tracking toward 3.1%, a raise that gets partly consumed by Medicare before it ever hits a checking account. With average annual household spending running $78,535 in 2024, healthcare is one of the few line items retirees can actually control by picking the right plan.

What to Do Between Now and December 7

Three concrete steps before the window closes:

1. Open the Annual Notice of Change and read the premium, deductible, and formulary sections.

2. Run the current prescription list through Medicare.gov's Plan Finder and sort by total annual cost, not premium.

3. Before dropping Medicare Advantage, confirm in writing whether a Medigap policy will be issued without underwriting in the relevant state.

The fall window is short, but the decisions made inside it price the entire following year.

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