Medicare: Enrollment, Coverage, Appeals, and What It Does Not Pay For

Summary. This article explains who is eligible and when, why missing an enrollment period produces a lifetime penalty, what each part covers and what none of them cover, why observation status can eliminate the skilled nursing benefit, why the improvement standard is not the law, how the five-level appeal process works, how Medigap guaranteed issue operates, and the programs that reduce costs.

Almost every serious Medicare problem is a timing problem.

A person who delays Part B enrollment pays a penalty every month for the rest of their life. A person who buys a Medicare Advantage plan and later wants to switch to original Medicare with a supplement may find that no insurer will sell them one. A person admitted to a hospital "under observation" for four nights discovers that the skilled nursing benefit they were counting on does not exist. A person who throws away a notice about services ending forfeits an appeal that would have been decided in two days.

None of those is a coverage dispute. Each is a deadline, and each is irreversible.

Part I: Eligibility

Age 65 with work credits. 42 U.S.C. § 426 provides entitlement to hospital insurance for individuals aged 65 and over who are entitled to Social Security or Railroad Retirement benefits. Premium-free Part A generally requires 40 quarters of Medicare-covered employment — by the individual, or by a spouse (including a divorced spouse married at least ten years, or a deceased spouse).

Under 65 with a disability. Entitlement generally begins after 24 months of Social Security Disability Insurance entitlement. There is no waiting period for ALS, and people with end-stage renal disease qualify on their own separate track.

Without enough work credits, Part A may be purchased at a monthly premium, and the premium is lower for those with some quarters of coverage.

Part II: The enrollment periods — where the money is lost

The Initial Enrollment Period runs seven months: the three months before the month of the 65th birthday, the birthday month, and the three months after. Enrolling before the birthday month produces coverage beginning that month; enrolling later delays it.

The General Enrollment Period, 1 January to 31 March each year, is the fallback for those who missed the initial period, with coverage beginning the month after enrollment.

The Special Enrollment Period is the one that matters most and is most misunderstood. A person covered by a group health plan based on current employment — their own or a spouse's — may delay Part B without penalty and enroll during an eight-month period beginning when the employment or the coverage ends, whichever comes first.

The three traps inside that rule:

COBRA is not current employment coverage. Neither is retiree coverage. A person who retires, takes COBRA, and waits for it to run out has been accruing a Part B penalty the whole time and has usually missed the special enrollment period.
The employer must be large enough. Where the employer has fewer than 20 employees, Medicare is generally the primary payer at 65 and the group plan is secondary — which means a person who delays Part B may have almost no coverage without knowing it.
The eight months run from the end of employment or coverage, whichever is first, not from the end of COBRA.

The penalties are permanent.

Part B: 10% of the standard premium for each full 12-month period of delayed enrollment, added to the premium for life.
Part D: 1% of the national base beneficiary premium for each month without creditable prescription coverage, also for life.
Part A (for those who must buy it): 10%, for twice the number of years of delay.

Automatic enrollment applies to people already receiving Social Security at 65, and to those receiving SSDI at month 25. Part B may be declined, and for someone with current-employment group coverage, declining is frequently correct.

Part III: The four parts

Part A — hospital insurance. Inpatient hospital care, skilled nursing facility care after a qualifying stay, home health, and hospice. Financed by payroll taxes and usually premium-free. It has a deductible per benefit period rather than per year, and a benefit period ends after 60 consecutive days without inpatient or skilled care — which means a person can incur multiple deductibles in a year.

Part B — medical insurance. Physician services, outpatient care, durable medical equipment, laboratory and imaging, and preventive services. A monthly premium, an annual deductible, and generally 20% coinsurance with no out-of-pocket maximum — which is the single most important structural fact about original Medicare.

Part C — Medicare Advantage. Private plans that replace Parts A and B, under 42 U.S.C. § 1395w-21. They must cover everything original Medicare covers, typically include Part D, frequently add dental, vision, and hearing benefits, and have an annual out-of-pocket maximum that original Medicare lacks. In exchange: networks, prior authorization, and referral requirements that original Medicare does not impose.

Part D — prescription drugs, under 42 U.S.C. § 1395w-101. Private plans with formularies, tiers, prior authorization, and step therapy. Recent legislation added an annual out-of-pocket cap and a monthly payment smoothing option, which changed the arithmetic substantially for people on expensive drugs.

Medigap (Medicare Supplement). Standardized private policies that pay the cost sharing original Medicare leaves. They cannot be used with Medicare Advantage. Part V explains why the timing of the purchase is the most consequential decision most beneficiaries make.

Part IV: What Medicare does not cover

42 U.S.C. § 1395y sets out the exclusions, and the general rule is that Medicare pays only for items and services that are reasonable and necessary for the diagnosis or treatment of illness or injury.

The exclusions that surprise people most:

Long-term custodial care. Help with bathing, dressing, eating, and toileting — the actual content of long-term care — is not a Medicare benefit at any point. This is the single largest misconception about the program. See Elder Law and Long-Term Care.
Most dental, vision, and hearing care, including dentures, routine eye exams, eyeglasses, and hearing aids. Many Medicare Advantage plans add limited coverage.
Care outside the United States, with narrow exceptions.
Cosmetic surgery, and services not reasonable and necessary.

The skilled nursing benefit and its two traps. Part A covers a stay in a skilled nursing facility for up to 100 days per benefit period — full payment for days 1 through 20, and a substantial daily coinsurance for days 21 through 100. It requires a qualifying inpatient hospital stay of three consecutive days, and it ends when skilled care is no longer required.

Trap one: observation status. A patient may occupy a hospital bed for four nights and be classified as an outpatient under observation the entire time. Observation days do not count toward the three-day inpatient requirement, and the patient discovers this at discharge, when the skilled nursing facility asks for private payment. Hospitals must give a written notice when observation status extends beyond a stated number of hours; read it, and ask the attending physician to reconsider the status while you are still in the hospital, because it cannot be fixed afterward.

Trap two: the improvement standard. Providers and contractors frequently terminate skilled coverage on the ground that the patient has "plateaued" or is "not improving." That is not the law. Coverage does not require improvement — skilled care necessary to maintain a condition or to prevent or slow deterioration can qualify. This was the subject of a nationwide settlement and formal CMS guidance, and it remains one of the most commonly misapplied rules in the program.

Part V: Medigap, and the window that closes

This is the most consequential and least understood decision in Medicare.

The open enrollment period is a six-month window beginning the first month a person is 65 and enrolled in Part B. During it, an insurer must sell any policy it offers, at the best available rate, without medical underwriting and without regard to health conditions.

After that window closes, in most states an insurer may refuse to sell, or may charge more, based on health. There are guaranteed issue rights in defined circumstances — losing employer coverage, a Medicare Advantage plan leaving the service area, moving out of a plan's area, an insurer's misconduct, and the 12-month trial right for someone who joined Medicare Advantage at 65 and disenrolls within a year — but outside those, there is no right to buy.

The practical consequence. A person who chooses Medicare Advantage at 65 for its lower premium and additional benefits may, at 78 with a new diagnosis, find that they cannot switch to original Medicare with a supplement because no insurer will underwrite them. They may switch to original Medicare, but they would face 20% coinsurance with no out-of-pocket maximum and no supplement to cover it.

A handful of states require continuous or annual guaranteed issue, which changes this analysis entirely. Find out which kind of state you live in before choosing.

Part VI: Appeals — five levels, and one that works in two days

42 U.S.C. § 1395ff establishes the appeal structure, with procedures at 42 C.F.R. Part 405.

Original Medicare, five levels:

Redetermination by the Medicare Administrative Contractor — 120 days to file, 60 days to decide.
Reconsideration by a Qualified Independent Contractor — 180 days to file.
Administrative Law Judge hearing — 60 days to file, subject to an amount-in-controversy threshold. This is the level at which a meaningful share of denials are reversed, and it is where representation begins to matter.
Medicare Appeals Council — 60 days.
Federal district court — 60 days, subject to a higher amount in controversy.

Medicare Advantage and Part D have parallel structures with different names — plan reconsideration, then an independent review entity, then an ALJ — and expedited timeframes of 72 hours for urgent requests.

The expedited review that matters most. When a hospital, skilled nursing facility, home health agency, or hospice is about to end services, the beneficiary receives a written notice — a Notice of Medicare Non-Coverage, or for hospital discharge an Important Message from Medicare. That notice carries a right to an immediate, free review by a Quality Improvement Organization, decided within about two days, with services continuing during the review.

Most people throw the notice away. The phone number is on it. Calling it is the single highest-value action available to a Medicare beneficiary, and it costs nothing.

Also request the "demand bill." Where a provider says Medicare will not pay but the beneficiary disagrees, the provider can be required to submit the claim so that Medicare, not the provider, makes the coverage decision — which creates an appealable determination where otherwise there would be none.

Part VII: Costs, and the programs that reduce them

IRMAA. Higher-income beneficiaries pay an income-related monthly adjustment on Parts B and D, based on the tax return from two years earlier. A person who retires and whose income drops can request a redetermination based on a life-changing event — work stoppage or reduction, marriage, divorce, death of a spouse, loss of income-producing property, or loss of a pension. This request is routinely granted and rarely made.

Medicare Savings Programs. State-administered, Medicaid-funded programs that pay the Part B premium and, at lower income levels, deductibles and coinsurance. The QMB program in particular prohibits providers from billing the beneficiary for Medicare cost sharing at all — a protection frequently violated by billing offices that do not know the person is a QMB.

Extra Help (the Part D Low-Income Subsidy), which substantially reduces or eliminates Part D premiums, deductibles, and copayments.

State Pharmaceutical Assistance Programs, in many states.

Medicaid, for those who qualify — dual eligibles receive both, with Medicare paying first.

These programs are collectively worth thousands of dollars a year and are substantially under-enrolled. The State Health Insurance Assistance Program (SHIP) in every state provides free, unbiased counseling and will screen for all of them.

Part IX: Choosing between Medicare Advantage and original Medicare

This is the decision most beneficiaries make with the least information, and it is substantially irreversible.

The honest comparison:

	Original Medicare + Medigap + Part D	Medicare Advantage
Monthly cost	Part B + Medigap premium + Part D premium — higher and predictable	Part B + frequently $0 plan premium — lower upfront
Cost at the point of care	Little to nothing, with a comprehensive Medigap	Copays and coinsurance up to the out-of-pocket maximum
Out-of-pocket maximum	None in original Medicare — the supplement supplies the protection	Yes, an annual cap
Providers	Any provider accepting Medicare, nationwide	Network; out-of-network is limited or not covered
Prior authorization	Rare	Common, including for hospital stays and post-acute care
Referrals	No	Frequently required (HMO)
Extra benefits	No	Dental, vision, hearing, fitness, sometimes transportation
Travel	Covered anywhere in the U.S.	Emergency only outside the service area
Switching later	Can join an Advantage plan any year	May require medical underwriting to buy a Medigap policy

Who is generally better served by original Medicare with a supplement: people with a serious chronic condition or a specialist relationship they want to keep; people who travel or live in two states; people who want to avoid prior authorization; and anyone who values predictability over a lower premium.

Who is generally better served by Medicare Advantage: people in good health with a low expected use, people who need the dental, vision, and hearing benefits, people for whom the Medigap premium is genuinely unaffordable, and people whose providers are all in one network anyway.

The asymmetry that should drive the decision. Choosing original Medicare with a supplement at 65 preserves the option to move to Advantage at any later annual enrollment. Choosing Advantage at 65 may foreclose the reverse move, because in most states a Medigap insurer may underwrite after the six-month window closes — except during the 12-month trial right for someone who joined Advantage at 65 and disenrolls within a year.

Which means the trial right is worth knowing about specifically. A person who takes Advantage at 65 and dislikes it has twelve months to switch to original Medicare with guaranteed issue of a supplement. After month twelve, in most states, that door closes.

And check your state. A handful require continuous or annual guaranteed issue, which removes the asymmetry entirely and makes the decision genuinely reversible.

Part X: Annual review — the hour that saves the most money

Plans change every year, and so do the drugs a person takes. The single most valuable Medicare habit is a one-hour annual review during open enrollment, 15 October to 7 December.

What to check, in order:

The Annual Notice of Change, which every plan mails in September. It states what is changing: premium, deductible, copays, network, and formulary. Most people discard it.
The formulary, against the drugs you actually take. Check each drug: is it still covered, at what tier, and does it now require prior authorization or step therapy? A drug moved from tier 2 to tier 4 can change annual cost by thousands.
The network, against the providers you actually see, by name. Check the plan's current directory, and then call the office to confirm — directories are frequently wrong.
The total expected cost, not the premium: premium plus deductible plus expected copays plus the out-of-pocket maximum in a bad year.
Star ratings and complaint data, which are published.
Whether a Part D plan change would lower costs — the plan finder compares total annual cost including your specific drugs, and the cheapest plan for one person is frequently expensive for another.

Two other enrollment windows to know: the Medicare Advantage Open Enrollment Period, 1 January to 31 March, during which an Advantage enrollee may switch plans or return to original Medicare; and the Special Enrollment Periods triggered by a move, a loss of other coverage, a plan leaving the area, or qualifying for Extra Help or a Medicare Savings Program.

And a caution about marketing. Medicare plan marketing is heavily regulated and heavily practiced. A broker paid a commission may present a narrow set of options, and a plan may not call you unsolicited. The unbiased source is your State Health Insurance Assistance Program, which is free, is not compensated by plans, and will run the comparison with you.

Part XI: Coordination with other coverage

Medicare rarely operates alone, and the order of payment determines who pays what.

Employer group health plan. Where the employer has 20 or more employees and coverage is based on current employment, the group plan pays first and Medicare second. Where the employer has fewer than 20, Medicare generally pays first — which means a person who delayed Part B in reliance on small-employer coverage may have a substantial gap. This is the most consequential coordination question in the program, and it should be confirmed with the employer in writing.

Retiree coverage and COBRA are secondary to Medicare, and neither supports a special enrollment period.

Medicaid. Dual eligibles receive both, with Medicare paying first and Medicaid covering cost sharing and services Medicare does not — most importantly long-term custodial care. See Elder Law and Long-Term Care. QMB status prohibits providers from billing the beneficiary for Medicare cost sharing at all, a protection routinely violated by billing offices.

TRICARE for Life, which requires Part B enrollment and then pays as secondary — a person eligible for TRICARE who declines Part B can lose the benefit entirely.

VA health care operates in parallel rather than coordinating: VA covers care at VA facilities, Medicare covers care elsewhere, and a veteran who relies solely on VA and declines Part B accrues a lifetime penalty and has no coverage outside the VA system.

Workers' compensation, liability insurance, and no-fault are primary to Medicare under the Medicare Secondary Payer provisions of 42 U.S.C. § 1395y. Two consequences: Medicare may make a conditional payment and then seek reimbursement from a settlement, and a settlement resolving future medical expenses may require a Medicare set-aside to protect the program's interest. Any personal injury or workers' compensation settlement involving a Medicare beneficiary must account for this, and doing it after the fact is far harder than doing it during negotiation. See Personal Injury Claim Toolkit.

Health savings accounts. Contributions must stop when Medicare begins, and enrollment in Part A is retroactive up to six months for someone who enrolls after 65 — which can create excess contributions and a tax penalty for a person who worked past 65 while contributing to an HSA. Stop contributions six months before enrolling.

Part XI-A: Four situations, worked through

The four-night hospital stay that was not a hospital stay. A 79-year-old falls, is taken to the emergency department, and occupies a bed for four nights while cardiac and neurologic causes are excluded. At discharge the hospital recommends a skilled nursing facility for rehabilitation. The facility asks for $11,000 in advance.

Why. All four nights were billed as observation — outpatient status. Observation days do not count toward the three-day inpatient requirement, so the Part A skilled nursing benefit never attached.

What would have worked. Asking, on day one, "Am I an inpatient or under observation?" and asking the attending physician to reconsider the status while still admitted. The written notice hospitals must provide when observation extends beyond a stated number of hours is the trigger, and it is routinely set aside unread. After discharge it cannot be fixed.

The therapy that stopped because she "plateaued." A woman with Parkinson's disease receives home physical therapy. At week seven the agency issues a Notice of Medicare Non-Coverage: she is not improving.

Why that is wrong. Coverage does not require improvement. Skilled care necessary to maintain a condition or to prevent or slow deterioration can qualify — the subject of a nationwide settlement and formal CMS guidance.

What worked. Her daughter called the QIO number printed on the notice. The expedited review was decided in two days, services continued during it, and the termination was reversed. Cost: one phone call.

The Part B penalty that ran for eleven years. A man retired at 65 with employer coverage, elected COBRA, and enrolled in Part B when COBRA ended eighteen months later.

Why it cost him. COBRA is not current-employment coverage. His special enrollment period began when his employment ended, not when COBRA ended, and it expired eight months later. He enrolled during a General Enrollment Period with a 10% permanent premium increase, paid every month for the rest of his life.

What would have worked. Enrolling in Part B at retirement and using COBRA, if at all, as secondary coverage.

The Medigap door that closed. A woman chose a $0-premium Medicare Advantage plan at 65 in good health. At 78, diagnosed with a condition requiring a specialist three states away who is out of network, she tries to switch to original Medicare with a supplement.

What she finds. She may return to original Medicare at the next enrollment period — but no insurer in her state will sell her a Medigap policy, because the six-month guaranteed issue window closed thirteen years earlier and she is now subject to underwriting. Original Medicare without a supplement means 20% coinsurance with no out-of-pocket maximum.

The window she missed. The 12-month trial right — had she disenrolled within a year of joining Advantage at 65, she would have had guaranteed issue.

The pattern in all four: none was a coverage dispute. Each was a deadline, a status, or a notice — and each was decided before anyone knew a decision was being made.

Part XI-B: Medicare Advantage denials, which behave differently

An Advantage plan must cover everything original Medicare covers, but it administers that coverage like private insurance — with networks, prior authorization, and concurrent review that original Medicare does not impose. That difference generates a distinct set of disputes.

The recurring pattern is post-acute care. An enrollee is hospitalized, discharged to a skilled nursing facility, and the plan authorizes a short stay and then terminates coverage — frequently applying proprietary criteria more restrictive than Medicare's own coverage rules. A plan may not apply criteria stricter than original Medicare's, and where it does, that is the argument: the plan's internal tool is not the standard, and the Medicare coverage rules are.

The appeal path is parallel but faster. Plan reconsideration → an independent review entity → an ALJ → the Appeals Council → federal court, with 72-hour expedited timeframes for urgent requests. Two features matter: the plan must forward an adverse reconsideration to the independent entity automatically, and the expedited track is available on request whenever delay could seriously jeopardize health or function.

And the QIO fast-track applies here too. When a skilled nursing facility, home health agency, or hospice is ending services, the Notice of Medicare Non-Coverage and the immediate QIO review are available to Advantage enrollees on the same terms — decided in about two days, with services continuing.

Prior authorization is the other front. Where a service is denied for want of prior authorization, ask three questions: does original Medicare require authorization for this service (usually not); did the plan's own materials disclose the requirement; and was the situation emergent, in which case authorization cannot be required.

Network and access issues. A plan must maintain an adequate network. Where no in-network provider with the necessary expertise is available within a reasonable distance, the plan must arrange out-of-network care at in-network cost sharing — a right that is rarely volunteered and frequently granted on request.

Where to complain. Beyond the appeal: 1-800-MEDICARE, which routes complaints to CMS and generates a plan response; the state insurance department, for marketing and enrollment misconduct; and the SHIP, which will help file. CMS tracks complaint volumes and uses them in star ratings and enforcement, which is why they produce movement.

And the retrospective denial deserves its own note: where a plan authorized a service and later refused payment, raise the authorization, any recorded confirmation, and the plan's own obligation to honor it. Retroactive denial after authorization is disfavored and frequently reversed on the first appeal.

Part XI-C: Part D, and the drug problems people actually have

Prescription coverage generates more day-to-day friction than any other part of the program, and most of it is manageable.

The formulary is the plan. A plan's list of covered drugs, organized in tiers, with utilization controls attached: prior authorization, step therapy, and quantity limits. A plan may change its formulary during the year, but must generally give notice and, where a drug is removed, must continue covering it for enrollees already taking it or provide a transition supply.

The four requests that solve most problems:

A formulary exception, to cover a non-formulary drug. Requires a prescriber's supporting statement that formulary alternatives would not be as effective or would cause an adverse effect.
A tiering exception, to have a drug covered at a lower cost-sharing tier.
A prior authorization request, submitted by the prescriber.
A step therapy exception, on the ground that the required drug was already tried and failed, is contraindicated, or is expected to be ineffective.

The timeframes are short: a standard coverage determination in 72 hours, an expedited determination in 24 hours, and the same structure at the redetermination level. Ask for expedited review whenever waiting could seriously harm health — it is granted on the prescriber's statement.

The transition fill. A new enrollee, or an existing enrollee whose drug was removed from the formulary, is generally entitled to a temporary supply — typically a month — at the start of the year or on transition, to allow time to switch drugs or file an exception. Pharmacies frequently do not offer it; ask by name.

The out-of-pocket cap. Recent legislation added an annual cap on Part D out-of-pocket spending and an option to spread costs across monthly payments rather than paying a large amount at the start of the year. Both changed the arithmetic substantially for people on expensive drugs, and both are under-used because they are new.

Extra Help — the low-income subsidy — substantially reduces or eliminates Part D premiums, deductibles, and copayments, and it is badly under-enrolled. Apply through the Social Security Administration; there is no cost.

Two practical habits. Use the plan finder every year with your actual drug list, because the cheapest plan differs entirely by person and by year. And when a pharmacy quotes a surprising price, ask the pharmacist to run it as a formulary exception pending or to check the cash price — which is occasionally lower than the copay, and which the pharmacist may now tell you.

Part XI-D: Where to get free help

Medicare is the rare program with a well-funded, unbiased, free counseling network that almost nobody uses.

The State Health Insurance Assistance Program (SHIP) exists in every state under a different local name, is federally funded, and provides one-on-one counseling by trained volunteers and staff who are not paid by insurers. They will compare plans with your actual drug list, screen you for every cost-assistance program, explain a denial, and help file an appeal. This is the single best resource in the program and it costs nothing.

1-800-MEDICARE, for claims questions, plan complaints, and replacement cards. Complaints filed here are routed to the plan with a response obligation and are tracked by CMS.

The Quality Improvement Organization for your state — the number is on every Notice of Medicare Non-Coverage — for the two-day expedited review when services are ending.

The Medicare Rights Center and similar national organizations, which run free helplines and publish plain-language guides.

Your Area Agency on Aging, which houses SHIP counseling in many places and knows the local programs.

Legal aid and senior legal helplines, which handle Medicare appeals in most states, and the National Center on Law and Elder Rights for advocates.

Social Security, for enrollment, IRMAA redeterminations after a life-changing event, and Extra Help applications.

Your state Medicaid agency, for the Medicare Savings Programs — which pay the Part B premium and, at lower income levels, cost sharing.

Two cautions. A plan may not call you unsolicited, and a broker paid a commission may present a narrow set of options — neither is a reason to avoid brokers, but it is a reason to run the same comparison with a SHIP counselor. And be skeptical of anyone offering to "review your Medicare" who asks for your Medicare number: Medicare fraud frequently begins with exactly that call.

Part XII: Frequently asked questions

Do I have to enroll at 65? If you have coverage through current employment (yours or a spouse's) at an employer with 20 or more employees, you may generally delay Part B without penalty. COBRA and retiree coverage do not count.

What is the difference between Medicare Advantage and original Medicare with a supplement? Advantage has an out-of-pocket maximum, networks, prior authorization, and extra benefits. Original Medicare with a supplement has no network and predictable costs, but requires buying the supplement — and the right to buy one may not exist later.

Does Medicare pay for a nursing home? Only for skilled care, up to 100 days per benefit period, after a three-day inpatient stay, and only while skilled care is needed. Never for custodial long-term care.

They said I stopped improving and coverage is ending. The improvement standard is not the law. Skilled care to maintain a condition or prevent deterioration can qualify. Appeal.

What is observation status? Being treated as an outpatient while occupying a hospital bed. Those days do not count toward the three-day inpatient requirement for the skilled nursing benefit. Ask about your status on day one.

Can I switch plans? During annual open enrollment (15 October to 7 December), and during the Medicare Advantage open enrollment period (1 January to 31 March). But switching from Advantage back to original Medicare with a supplement may require underwriting.

How do I appeal? Follow the instructions on the denial notice. For services about to end, call the QIO number on the notice — that review is decided in about two days and services continue.

Part XIII: For beneficiaries and families — the ten things that matter

Enroll on time. The Part B and Part D penalties last for life. If you are delaying because of employment coverage, confirm in writing that it is current-employment coverage and that the employer has 20 or more employees.
Do not rely on COBRA or retiree coverage to protect a delayed enrollment. They do not.
Understand the Medigap window. Six months from Part B enrollment at 65, guaranteed issue. After that, in most states, underwriting. Choose with that in mind, not on the first year's premium.
On hospital admission, ask on day one: "Am I an inpatient or under observation?" Get the answer in writing, and ask the physician to reconsider the status if the clinical picture supports admission.
Never throw away a notice about services ending. Call the QIO number on it. The review is free, takes about two days, and services continue.
Do not accept "you've plateaued." Maintenance care can be covered.
Check the drug formulary every year against the drugs you actually take. Plans change formularies annually, and the plan that was cheapest last year frequently is not.
If your income dropped, request an IRMAA redetermination for a life-changing event.
Apply for the Medicare Savings Programs and Extra Help if income is limited. They are worth thousands a year and are badly under-enrolled.
Call your SHIP. Free, unbiased, one-on-one counseling in every state, and they will screen for everything in item 9.

Primary authority

42 U.S.C. § 426 — entitlement to hospital insurance.
42 U.S.C. § 1395 — the program's foundational provision.
42 U.S.C. § 1395x — definitions, including the terms that determine what services are covered.
42 U.S.C. § 1395y — exclusions, the reasonable-and-necessary standard, and Medicare secondary payer.
42 U.S.C. § 1395ff — determinations and the five-level appeal structure.
42 U.S.C. § 1395w-21 — Medicare Advantage eligibility, election, and enrollment.
42 U.S.C. § 1395w-101 — Part D eligibility and enrollment.
42 U.S.C. § 1395i-3 — skilled nursing facility requirements.
42 C.F.R. Part 405 — claims, determinations, and appeals procedures.