One envelope lands in every Medicare Advantage and Part D enrollee’s mailbox no later than September 30, and what it says determines whether 2027 coverage costs more, covers less, or drops a favorite doctor. Federal regulation requires every renewing Medicare Advantage and Part D plan to mail an Annual Notice of Change listing next year’s premiums, deductibles, drug formulary and network terms before Medicare’s Annual Enrollment Period opens October 15. Enrollees who set the letter aside and take no action are automatically kept in whatever plan the changes describe, however much pricier it has become.
The Notice Every Medicare Advantage and Part D Plan Must Send
The mailing is not left to chance or plan discretion. Every renewing Medicare Advantage and Part D plan must send an Annual Notice of Change to each enrollee before the fall enrollment window opens, spelling out the premium, deductible, drug formulary and network terms that will apply starting January 1. Missing that mail-by date is treated as a compliance failure, not a paperwork delay, and the requirement applies whether the plan is a national insurer or a small regional carrier with only a few thousand members.
Under 42 C.F.R. §§422.111(a) and 423.128(a), the Centers for Medicare & Medicaid Services can pursue compliance action against any Medicare Advantage organization or Part D sponsor that files a late or inaccurate notice, and CMS requires the plan to log the actual date each letter was mailed. That enforcement is a large part of why the letter almost always lands in the final two weeks of September instead of trickling out through October.
The notice sometimes arrives folded into the plan’s Evidence of Coverage rather than as its own envelope, which is part of why so many people mistake it for renewal boilerplate and set it aside unread. Reading the Annual Notice of Change for the coming plan year means checking the premium and deductible lines first, then the maximum out-of-pocket figure, since a Medicare Advantage plan can raise that ceiling by thousands of dollars without technically dropping any covered service.
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Premiums, Networks and Formularies Can All Shift for 2027
Cost figures are only the most visible line item in the notice. A Medicare Advantage plan can raise its monthly premium, restructure copays for specialist visits and inpatient stays, or swap a flat drug copay for percentage-based coinsurance, and every one of those changes must be spelled out in the letter rather than discovered at the pharmacy counter in January. Because insurers file these terms with CMS each summer, the notice reflects contract terms already locked in for 2027, not a draft still open to negotiation.
Provider network changes tend to draw less attention than premiums but carry more consequence for people mid-treatment. A plan can drop a hospital system, a specialist group or an entire county from its service area, and the same notice is where a beneficiary discovers whether a particular oncologist, cardiologist or primary care practice will still be in-network come January 1. Losing an in-network specialist mid-course of treatment can mean restarting prior authorization paperwork from scratch with a new provider.
Drug formulary shifts follow a similar pattern. A medication can move to a higher cost tier, pick up a new prior authorization or step-therapy requirement, or disappear from the covered list entirely, and none of those changes require the plan to contact the enrollee again before January 1 — the September letter is the only individualized warning most people receive.
Passive Re-Enrollment Is the Trap Buried Inside the Letter
None of those changes trigger an automatic switch to something better. Under CMS’s open enrollment rules, a Medicare Advantage or Part D enrollee who takes no action during the window from October 15 through December 7 is simply carried into the same plan for 2027 on whatever new terms the notice describes, as long as that plan is still offered in the area. The only exception is a plan that is leaving Medicare entirely, which triggers a separate non-renewal notice rather than a routine change letter.
That default protects against a coverage gap, not against cost. A beneficiary who ignores a premium increase, a narrowed network or a reshuffled formulary carries all three into the new year without ever comparing alternatives, and advocacy groups that track the mailing note that the Annual Notice of Change is typically the only individualized heads-up a plan is required to send before that happens.
Comparing the notice against alternatives takes only the tool CMS already publishes. Medicare’s plan finder at medicare.gov/plan-compare lets an enrollee enter a ZIP code and current drug list to see every Medicare Advantage and Part D option available for 2027 side by side with existing coverage, and any switch made through the tool during the enrollment window takes effect January 1. The September letter itself is neutral information; the expense only shows up for whoever never opens it.
This article was produced with the assistance of AI and reviewed by The Money Overview editorial team before publication.
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