A plain envelope from a Medicare Advantage insurer, arriving in a mailbox in the first days of October, is rarely a coincidence. Federal regulation dictates that timing down to the calendar day. When an insurer decides not to renew its Medicare Advantage contract with the federal government, it cannot notify enrollees whenever it gets around to it — the rule fixes a floor of 90 calendar days before the plan disappears. For coverage ending on December 31, that floor pushes the mailing into early October, weeks before most retirees start paying attention to Medicare’s fall enrollment season.
The 90-Day Notice Rule Under 42 CFR 422.506
The requirement traces to a single subsection of the Medicare Advantage regulations governing contract nonrenewal. An insurer, formally a Medicare Advantage organization, that elects not to renew its contract with the Centers for Medicare & Medicaid Services has to clear two separate deadlines rather than one. It must tell the agency in writing by the first Monday in June of the year the contract would end, long before most enrollees have any idea a change is coming. Separately, and later in the year, it must tell each enrollee by mail, and that enrollee-facing deadline is the 90-day floor that ultimately determines when the letters go out.
The regulatory text leaves no room for a shorter runway. Under the current version of 42 CFR 422.506(a)(2), maintained by the Office of the Federal Register and current as of September 4, 2026, a nonrenewing organization must notify each Medicare enrollee by mail “at least 90 calendar days before the date on which the nonrenewal is effective.” That enrollee-notice language has carried the same 90-day floor since a 2010 amendment, with only the alternative-plan-information provisions revised since.
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Why a December 31 Termination Means an Early-October Postmark
Medicare Advantage contracts run on the calendar year, and a nonrenewal almost always takes effect on December 31, the final day of the contract term. Counting back 90 calendar days from December 31, 2026 lands on October 2, 2026. That date marks the outer edge of when a mailed notice can still satisfy the regulation; an insurer that has not put the letter in the mail by then has already violated the rule, regardless of when the enrollee ultimately opens it.
Nothing in 42 CFR 422.506 sets October as a fixed calendar deadline the way CMS’s own rule sets the first Monday in June for the agency notification. October is simply where the arithmetic lands once a fixed 90-day floor is applied to a fixed December 31 contract-year end. An insurer facing that floor typically builds in a buffer rather than mailing at the last legally permissible moment, which is one reason termination notices tend to cluster across the first half of October rather than arrive as a single wave on one date.
What the Insurer Must Tell Enrollees Besides the Termination Date
The mailed notice cannot simply announce that coverage is ending. The same regulation requires the insurer to also supply information about alternative enrollment options, satisfied through one of two methods: a CMS-approved written description of the other Medicare Advantage, Medicare Advantage-Part D, and standalone Part D plans available in the enrollee’s region, or outbound phone calls placed to every affected enrollee so each one knows who to contact about their options.
CMS controls the content of both channels rather than leaving the message to the departing insurer. An organization cannot fold its own marketing pitch into the termination notice or use the required outbound calls to sell a replacement product it also sells; the written description and the call script both have to track the agency’s approved format, which is part of why the notice reads as a compliance document rather than a sales letter.
The Enrollment Windows That Open When the Letter Arrives
The October notice does not leave enrollees to navigate the change on their own timeline. A nonrenewal effective January 1 overlaps with Medicare’s Annual Enrollment Period, which the Centers for Medicare & Medicaid Services’ current enrollment and disenrollment guidance for the 2026 plan year confirms runs October 15 through December 7 and is open to every Medicare beneficiary selecting coverage for the following year.
A second, narrower window exists specifically for enrollees whose plan is not renewing. Under Medicare’s own Special Enrollment Periods guidance, that window begins December 8 and runs through the last day of the following February, giving affected enrollees roughly three additional months beyond the ordinary fall enrollment period to pick a replacement Medicare Advantage or Part D plan.
Enrollees Who Take No Action Default to Original Medicare
Silence has a default outcome, and it is not continued coverage under the old plan. CMS’s enrollment guidance states that an enrollee who does not elect a new plan before the nonrenewal’s effective date is defaulted into Original Medicare on that same date, with no application required to trigger the switch. The special enrollment period tied to the nonrenewal does remain open for one additional month after the effective date, so a late decision is not entirely foreclosed.
That default carries a real financial consequence for a household that lets the window close without acting. An enrollee who reaches March without selecting a new Medicare Advantage or Part D plan is left in Original Medicare’s Part A and Part B benefits alone, with no drug coverage until the next enrollment opportunity, unless the special enrollment period tied specifically to the nonrenewal is used before it expires at the end of February.
This article was produced with the assistance of AI and reviewed by The Financial Wire editorial team.
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David M. Keller is a finance writer based in Columbus, Ohio, covering personal finance and consumer-focused economic topics. He earned his degree in journalism from Ohio University and began his career reporting on local business and economic trends for a regional media outlet. Since then, he has contributed to a variety of online publications, focusing on clear, practical coverage of topics such as cost of living, debt, and everyday financial decision-making.
