Original Medicare pays a substantial share of hospital and medical bills, but Parts A and B were never built with a ceiling on what a patient spends out of pocket in a year. Each carries its own deductible, and Part B layers on a flat 20 percent coinsurance that keeps accruing with no stopping point written into the statute. For a retiree who is hospitalized, moves into a skilled nursing facility, and then needs months of outpatient treatment in the same year, those separate charges can compound into tens of thousands of dollars before December closes the books. That structural gap, not a glitch, is the reason a private supplemental insurance market exists alongside the federal program.
What Part A and Part B Actually Leave Uncapped
Part A, which covers inpatient hospital care, charges a deductible of $1,736 for each benefit period in 2026, and there is no limit on how many benefit periods a person can rack up in a single year. A benefit period ends only after 60 consecutive days without inpatient care, so someone discharged and then readmitted within two months starts a fresh deductible rather than continuing a shared one. Once inside a hospital stay, the bill keeps climbing: days 61 through 90 carry a $434-per-day coinsurance, days 91 through 150 draw on a lifetime bank of 60 reserve days at $868 per day, and anything beyond day 150 is billed in full to the patient. A skilled nursing facility stay adds its own coinsurance of $217 per day from day 21 through day 100, on top of whatever hospital charges preceded it.
Part B behaves the same way. The annual deductible is $283, and after that a beneficiary owes 20 percent of the Medicare-approved amount for nearly every covered service, including physician visits, outpatient surgery, chemotherapy infusions, durable medical equipment, dialysis and outpatient mental health care, for as long as the treatment continues. No dollar figure exists at which that 20 percent share simply stops. A single complex surgery followed by months of physical therapy, or a cancer diagnosis that requires repeated infusions, can generate a coinsurance bill running into the tens of thousands, while the monthly Part B premium of $202.90 keeps being charged separately on top of it.
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The Out-of-Pocket Cap Congress Built Into Medicare Advantage, Not Original Medicare
Congress required something different for Part C. Every Medicare Advantage plan must include an annual limit on what an enrollee pays for Part A- and Part B-covered services, and once a member reaches that limit the plan is required to pay 100 percent of covered costs for the rest of the calendar year, according to Medicare’s official cost guidance. That legal backstop has no counterpart in Original Medicare. A beneficiary who stays with traditional Part A and Part B carries open-ended exposure by design, because the underlying fee-for-service program was never given the stop-loss provision that later law wrote into private Medicare Advantage plans.
That difference shapes very different decisions at 65. A retiree who anticipates a lighter healthcare year and wants coordinated, often lower-premium coverage may lean toward Medicare Advantage largely because of its built-in ceiling. A retiree who wants the widest possible choice of doctors and hospitals nationwide, without referrals or narrow provider networks, often keeps Original Medicare and instead looks for a separate way to cap the exposure that comes with it.
Medigap: The Private Backstop Original Medicare Doesn’t Provide
Medicare Supplement Insurance, sold by private insurers and known as Medigap, exists specifically to absorb the coinsurance, copayments and deductibles that Parts A and B leave to the beneficiary. A person who buys a Medigap policy pays a separate monthly premium to the insurer, on top of the Part B premium, and in exchange the policy picks up some or all of the cost-sharing that would otherwise accumulate without limit. Coverage varies by which standardized plan letter a person selects: some of the most widely sold plans cover the full Part A hospital coinsurance and the entire 20 percent Part B coinsurance, leaving only the modest annual Part B deductible as an out-of-pocket item, while other plan letters shift small copays back onto the policyholder in exchange for a lower monthly premium.
Timing determines whether that protection is affordable. Federal law gives each beneficiary a six-month Medigap open enrollment period that starts the month a person is both 65 or older and enrolled in Part B; during that window, an insurer cannot use a person’s health history to deny a policy or charge more for one. Outside that window, insurers in most states may medically underwrite an application, reviewing health history and pricing or denying coverage accordingly, except in specific federally guaranteed-issue circumstances such as losing employer coverage or a Medicare Advantage plan exiting the area. A retiree who skips the enrollment window and later develops a chronic condition can find Medigap significantly more expensive, or unavailable, at the exact moment Original Medicare’s uncapped exposure becomes most relevant.
A Single Bad Year Can Erase the Savings of a Decade
The math turns concrete during an actual medical crisis. A retiree hospitalized twice in one year for two unrelated events, followed by weeks in a skilled nursing facility, could face two separate Part A deductibles, dozens of days of daily coinsurance, and months of 20 percent Part B coinsurance on specialist visits, imaging and rehabilitation, all stacking before a single one of those charges reaches a ceiling that does not exist under Parts A and B alone. Counselors who work with Medicare beneficiaries point to exactly this kind of stacked, multi-event year, rather than routine annual checkups, as the reason the coverage choice made at 65 can carry consequences that resurface a decade later, once a chronic diagnosis finally arrives and the enrollment window that would have guaranteed affordable Medigap coverage has long since closed.
This article was produced with AI assistance and reviewed by The Financial Wire editorial team.
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David M. Keller is a finance writer based in Columbus, Ohio, covering personal finance and consumer-focused economic topics. He earned his degree in journalism from Ohio University and began his career reporting on local business and economic trends for a regional media outlet. Since then, he has contributed to a variety of online publications, focusing on clear, practical coverage of topics such as cost of living, debt, and everyday financial decision-making.
