Millions of Medicare Advantage and Part D enrollees face a hard deadline this fall: their plans must send a written notice of every cost and coverage change taking effect January 1, 2027, no later than September 30. Federal regulation requires that delivery at least 15 days before the October 15 start of open enrollment. Anyone who tosses the envelope aside without reading it risks staying locked into a plan with higher premiums, narrower networks, or dropped benefits for the entire 2027 calendar year, because the window to switch closes December 7.
Why the September 30 ANOC deadline creates real financial exposure
The document in question is the Annual Notice of Change, or ANOC. Each fall, every Medicare Advantage organization and Part D drug plan sponsor is required to mail this notice to current enrollees. It spells out exactly what will be different about the plan starting January 1: premium increases, changes to copays, shifts in formulary drug tiers, added prior-authorization requirements, and any benefits being removed. The CMS consumer guidance on plan notices directs beneficiaries to review the ANOC carefully and to contact their plan if a copy does not arrive.
The timing is not arbitrary. Under 42 CFR Section 423.128, Part D sponsors must notify enrollees of plan rule changes at least 15 days before the Annual Coordinated Election Period begins. That election period starts October 15, which means September 30 is the latest permissible mailing date. A parallel requirement under 42 CFR Section 422.111 applies the same rule to Medicare Advantage organizations. Plans that miss this window face compliance risk, but the bigger consequence falls on enrollees who never receive or never open the notice.
Once open enrollment closes on December 7, beneficiaries are generally locked into whatever plan they hold for the full year. That makes the 54-day stretch between October 15 and December 7 the only reliable chance to compare options and switch. A person who ignores the ANOC and later discovers a steep premium hike or a dropped prescription drug has no routine mechanism to change plans until the following fall.
What CMS requires plans to disclose and how to use it
CMS instructs beneficiaries to review both the ANOC and the Evidence of Coverage, which is the longer document detailing all plan rules, costs, and covered services. The agency’s open enrollment partner resources repeat this guidance and encourage counselors, community organizations, and family members to help enrollees compare their current plan against alternatives.
Plans must follow the Medicare Communications and Marketing Guidelines when preparing these materials. CMS publishes model ANOC and EOC templates and issues operational memos through the HPMS system each contract year. For 2027, the specific HPMS memo governing ANOC submission and mailing requirements has not yet appeared in the public weekly archive, so plans are currently working from prior-year templates and the standing regulatory text.
