Updated August 7, 2026. Quick answer: Medicare notices are not interchangeable. 🔴 Some tell you what was already paid, some tell you a benefit is ending in two days, and only a few carry a deadline that expires almost immediately. This index sorts them by how fast you have to act.
The ones with a clock measured in hours
Notice of Medicare Non-Coverage (CMS-10123) — your skilled nursing, home health, hospice or rehab coverage is ending on a stated date. The fast-review request is due by noon of the calendar day after you receive it. A late request is still accepted, but the 72-hour decision clock and the financial-liability protection are lost. This is the most time-critical notice Medicare produces.
Its companion, the Detailed Explanation of Non-Coverage (CMS-10124), is issued only when you request the expedited review — it is where the provider must state its reasons.
The one with a season
The Annual Notice of Change — what your Advantage or Part D plan is changing for January 1, sent at least 15 days before the Annual Election Period. Doing nothing means accepting the changes.
The income-related one
An IRMAA determination raises your Part B and Part D premiums based on a tax return from two years earlier. It has its own cluster, because the rules around it are where the money is: what IRMAA is · the two-year lookback · why you usually want a new initial determination, not an appeal · why it is a cliff, not a slope.
⚠️ What this index does not cover yet
We would rather list the gaps than pretend the set is complete. Not yet decoded here: the Medicare Summary Notice (the quarterly “this is not a bill” statement), the Medicare Outpatient Observation Notice, Extra Help / Low-Income Subsidy award and redetermination letters, the Part B late-enrolment penalty letter, and the Advance Beneficiary Notice family. They are on CMS’s Beneficiary Notices Initiative page, and each will be added here only when its official text can be quoted rather than summarised.
The notice that arrives before you need any of the others
Where someone receives observation services as an outpatient for more than 24 hours, the hospital must give notice within 36 hours, and that notice must state the person is not an inpatient and explain what it means for later skilled-nursing coverage. Observation is not inpatient sets out why that single word decides who pays for the rehab afterwards.
What these pages do and do not do
These decoders explain what a notice says, what deadline it carries, and what happens next. They do not advise on paying, settling or negotiating anything, and they do not cover collection-stage instruments. Where a notice carries an appeal right, the appeal window is part of understanding the notice, and it is stated exactly.
Sources
Notice names and form numbers from CMS’s Beneficiary Notices Initiative; regulatory text from eCFR (42 CFR § 405.1200, § 405.1202, § 422.111), all retrieved 7 August 2026.