The simple version

Terms change at the turn of the year. The company behind your coverage can move what you pay monthly, what you pay when you actually use it, and which places it will pay for.

The rules do not let it make those changes quietly. A document has to reach you first, and the outside date for that is September 30.

The part worth knowing is where September 30 comes from. It is not a date chosen for neatness.

The numbers

• The rules cited here govern Medicare Advantage plans (42 CFR Part 422). The notice must be sent for receipt no later than September 30 of each year (42 CFR 422.2267(e)(3)(i))
• People with an October 1, November 1 or December 1 effective date must receive it within 10 calendar days from receipt of CMS confirmation of enrollment, or by the last day of the month before the effective date, whichever is later (42 CFR 422.2267(e)(3)(ii))
• The underlying rule requires notice at least 15 days before the Annual Coordinated Election Period begins, for changes taking effect January 1 (42 CFR 422.111(d)(2))
• For changes that do not take effect on January 1, the requirement is at least 30 days before the intended effective date (42 CFR 422.111(d)(3))
• The annual coordinated election period runs October 15 through December 7 each year (42 CFR 422.62(a)(2)(iii)), so the window for 2027 coverage is October 15 through December 7, 2026 (CMS, 2027 Medicare Advantage and Part D Star Ratings fact sheet, read October 9, 2026)
• The notice is a standardized marketing material through which plans provide the information 422.111(d)(2) requires (42 CFR 422.2267(e)(3)), and standardized materials must be used in the form and manner provided by CMS (42 CFR 422.2267(b))
• All required materials, standardized or model, must be in 12 point Times New Roman or equivalent (42 CFR 422.2267(a)(1))
• Where a contracted provider is terminated, notice runs at least 45 calendar days for primary care and behavioral health and at least 30 calendar days for other specialties (42 CFR 422.111(e))

Where September 30 comes from

Two rules govern the same document and they are written in different shapes. One of them names a calendar date. The other names a gap.

The gap rule says enrollees must be notified at least 15 days before the window in which they are allowed to change their minds. That window opens on October 15.

Count back 15 days from October 15 and you arrive at September 30, which is the date the first rule names. So the deadline is the opening worked backwards, and the 15 days is what you are guaranteed to read it in before you can do anything.

The actual math on 15 and 30

October 15 minus 15 days is September 30. That is the entire derivation, and the two rules agree because the one naming September 30 is how the one naming the gap gets carried out.

People who join in the closing months of the year get a different rule. Their clock starts when CMS confirms they have joined, because the annual deadline has already gone by before they arrive.

Fifteen days is a floor, not a promise of more. A document that lands exactly on the deadline has given you the least the rule allows.

What this means

The one document that tells you what changed is required to be with you about two weeks before you can act on it. That gap is deliberate rather than accidental.

It is also classified as a marketing material, and the rules specify the format of every required document, this one included, down to the typeface. The marketing label is part of why it can look like an advertisement and go in the recycling.

Worth noting what the two rules read here do not cover. They set deadlines and formats; they do not prescribe a side-by-side layout, and they say nothing about what follows if you do not respond.

What this is NOT

This article explains the deadline for the annual notice of change and where that deadline comes from, using 42 CFR 422.2267 and 42 CFR 422.111 as read on October 11, 2026, with the window dates from 42 CFR 422.62 and a CMS fact sheet. It is not advice about which plan to choose, and it is not a recommendation for or against Medicare Advantage, original Medicare, or any named insurer. It does not predict what any plan will charge or cover. It describes only what the two cited sections say: both set notice deadlines, and neither one, as read here, enumerates the categories of information the notice must contain or requires any particular side-by-side format, so no such requirement is asserted. Nothing here describes what happens to an enrollee who takes no action, because the sections read do not address it. The single piece of arithmetic, that October 15 minus 15 days is September 30, is ours, done on the dates the rules and the fact sheet give. Plan rules and notice practices vary, and anyone relying on a date should confirm it against their own documents. This is not a political endorsement or criticism of anyone.

Sources

• 42 CFR 422.2267, Required materials and content, paragraphs (a)(1), (b) and (e)(3), via govinfo CFR XML, read October 11, 2026
• 42 CFR 422.111, Disclosure requirements, paragraphs (d) and (e), via govinfo CFR XML, read October 11, 2026
• 42 CFR 422.62(a)(2)(iii), annual coordinated election period, via govinfo CFR XML, read October 11, 2026
• Centers for Medicare & Medicaid Services, "2027 Medicare Advantage and Part D Star Ratings" fact sheet, read October 9, 2026