What Does Medicare Mean? Parts, Costs & Coverage

Medicare is the federal health insurance program that covers most Americans aged 65 and older, along with younger people who have certain disabilities or end-stage kidney disease. It is not a single plan but a collection of parts, each covering different services with its own rules and costs. Understanding what Medicare actually means in practice requires looking past the label and into the details of what each part pays for, what you still owe, and how the system has evolved in ways that affect your wallet and your care.

The Four Parts of Medicare

Medicare is split into four distinct components, commonly called Parts A through D. Each covers a different slice of health care, and most beneficiaries interact with at least two or three of them.

Part A (Hospital Insurance): Covers inpatient hospital stays, skilled nursing facility care, hospice, and some home health services. Most people don’t pay a premium for Part A because they or a spouse paid Medicare taxes during their working years.
Part B (Medical Insurance): Covers outpatient care, doctor visits, preventive services, lab tests, durable medical equipment, and some home health care. Part B requires a monthly premium, which in 2025 is income-adjusted and starts at roughly $185 per month for most beneficiaries.
Part C (Medicare Advantage): A private-plan alternative to Parts A and B, offered by insurance companies that contract with Medicare. These plans must cover everything Original Medicare covers but often bundle additional benefits like dental, vision, hearing, and sometimes prescription drugs. They typically use provider networks.
Part D (Prescription Drug Coverage): Covers outpatient prescription medications through private plans. Available as a standalone plan for people in Original Medicare (Parts A and B) or built into most Medicare Advantage plans.

Parts A and B together are often called “Original Medicare” or “Traditional Medicare.” You can stay in Original Medicare and add a Part D plan for drug coverage, or you can choose a Medicare Advantage plan that replaces both Parts A and B and usually includes Part D.

Medicare Advantage and Its Rapid Growth

Medicare Advantage has grown from a niche alternative into the dominant choice for new enrollees. Switching from traditional fee-for-service Medicare to Medicare Advantage more than tripled between 2006 and 2022, while switching in the opposite direction declined, with both trends accelerating after 2019. By 2022, switchers made up about 80 percent of all new Medicare Advantage enrollees, up from 61 percent in 2011.¹

The appeal of Medicare Advantage is straightforward on the surface: these plans often have lower premiums than the combined cost of Original Medicare plus a Medigap policy, and they bundle extras like dental and vision coverage that Original Medicare lacks entirely. But the trade-off is network restrictions and utilization management tools that can limit how and where you receive care.

Research comparing the two systems shows meaningful differences in how much care gets used. Emergency department visits were about 30 percent lower in Medicare Advantage HMOs than in traditional Medicare in 2017, elective hip and knee replacements were roughly 10 percent lower, and back surgeries were nearly 30 percent lower. Quality performance was the same or higher in Advantage plans despite these lower utilization rates.² A separate analysis found similar patterns: spending for people with diabetes was about $5,200 in Medicare Advantage HMOs compared with roughly $6,400 in traditional Medicare, and emergency department use was consistently lower in Advantage plans.³

Whether lower utilization means better, more efficient care or restricted access to needed services is one of the most debated questions in health policy. The answer probably depends on the specific plan. Established, nonprofit, and larger health plans generally performed better on both resource use and quality than smaller, newer, for-profit plans.³

What You Actually Pay Out of Pocket

One of the biggest misconceptions about Medicare is that it covers everything once you turn 65. It does not. Medicare beneficiaries face premiums, deductibles, copays, and coinsurance, and the total bill can be substantial. More than a quarter of all Medicare beneficiaries, about 15 million people, spend 20 percent or more of their income on premiums and medical care combined. Overall, beneficiaries spent an average of about $3,000 per year on out-of-pocket costs.⁴

Chronic conditions make the financial pressure worse. Beneficiaries with any of the four most common chronic conditions (diabetes, heart disease, lung disease, and cancer) spent about 15 percent more on out-of-pocket costs and were 56 percent more likely to spend 20 percent or more of their annual income on health expenses compared with those without these conditions.⁵ For diabetes specifically, beneficiaries faced about $500 more per year in out-of-pocket costs than those without diabetes, and the prevalence of high financial burden was greatest among people in the lowest income groups.⁶

Income-related disparities in out-of-pocket burden are striking. While wealthier beneficiaries tend to spend more in absolute dollars, lower-income beneficiaries lose a far larger share of their income to medical costs. People near or below twice the poverty level and those with multiple chronic conditions face the greatest financial risk.⁴

Medigap and Supplemental Insurance

To fill the gaps in Original Medicare’s coverage, many beneficiaries buy supplemental insurance, commonly known as Medigap. These are standardized private policies labeled with letters (Plan A through Plan N) that cover some or all of the cost-sharing that Original Medicare leaves behind: deductibles, copays, and coinsurance. Medigap provides important financial protection, particularly for low- and moderate-income beneficiaries in the traditional fee-for-service program.⁷

There is a catch, though. Because Medigap policies cover most or all out-of-pocket costs, they can reduce the financial incentive for beneficiaries to limit their use of services. Research has found that supplemental insurance can blunt the impact of cost-sharing, increasing utilization and creating a spillover effect that raises costs for the primary insurer, in this case Medicare itself.⁸ This is one reason policymakers periodically debate whether to restructure Medigap, though any reform involves a difficult trade-off between protecting individuals and controlling overall program spending.

Medigap is only available to people enrolled in Original Medicare. If you choose Medicare Advantage, you cannot buy a Medigap policy, and if you switch back to Original Medicare after the initial enrollment window, insurers in most states can charge more or deny coverage based on pre-existing conditions.

Part D and the Inflation Reduction Act

Part D prescription drug coverage has gone through significant changes recently, driven by the Inflation Reduction Act (IRA) passed in 2022. The law introduced a $2,000 annual cap on out-of-pocket drug spending starting in 2025 and empowered Medicare to negotiate prices on certain high-cost drugs for the first time. One simulation estimated that if Medicare had paid negotiated ceiling prices for 37 selected drugs, spending could have been reduced by roughly $26.5 billion, nearly half, over a three-year period.⁹

But the picture is more complicated than “prices go down and everyone saves money.” Plan sponsors have responded to the IRA’s changes by adjusting their plan designs in ways that shift costs around rather than simply absorbing them. In Medicare Advantage plans, average Part D deductibles dropped from $153 in 2019 to $66 in 2024, but then jumped to $228 in 2025. The share of Advantage beneficiaries facing coinsurance rather than flat copays for preferred brand-name drugs exploded from under 3 percent to nearly 28 percent in 2025. Monthly out-of-pocket costs for nine high-spending brand-name drugs rose from a range of $46 to $55 per month in previous years up to $73 in 2025.¹⁰

Standalone Part D plans showed an even steeper trend, with average deductibles climbing steadily from $295 in 2019 to $490 in 2025, and the share of beneficiaries facing coinsurance for preferred brand-name drugs rising from about 22 percent to 84 percent. Monthly costs for those same nine drugs rose from $62 to $108 over the same period. Premiums, by contrast, decreased for both plan types.¹⁰ So while the new $2,000 annual cap protects people with very high drug costs, beneficiaries who don’t reach that cap may actually pay more than before thanks to higher deductibles and coinsurance.

Prior Authorization in Medicare Advantage

One of the most common complaints about Medicare Advantage plans involves prior authorization, the process where the plan requires approval before it will cover a treatment, test, or procedure. While Original Medicare rarely uses prior authorization, Advantage plans rely on it heavily. In 2021, more than 35 million prior authorization requests were submitted to Medicare Advantage plans. Plans denied, fully or partially, more than 2 million of those requests, yet only about 11 percent of denials were appealed.¹¹

That low appeal rate matters because when denials are appealed, a substantial fraction get overturned. The implication is that many beneficiaries accept a denial and go without the service, even when the denial might not have been appropriate. For people managing serious illnesses, a delayed or denied treatment can affect outcomes. Federal regulators have proposed reforms to streamline prior authorization and require greater transparency from plans, but implementation has been gradual.

How Turning 65 Changes Your Health Care

The transition to Medicare at age 65 is more than an administrative event. Research looking at what happens at the age boundary shows measurable shifts in how people receive care. One large study of trauma patients found that turning 65 and gaining Medicare was associated with a decrease in hospital stay length of about a third of a day per encounter, roughly a 5 percent reduction. At the same time, discharges to nursing homes increased by about 1.6 percentage points and transfers to other inpatient facilities rose, while discharges to home dropped by about 2 percentage points. Treatment patterns during the hospital stay itself, including potentially life-saving interventions like blood transfusions, did not change, and neither did mortality.¹²

Preventive care use also shifts at 65, but not always in the direction you’d hope. Medicare enrollment led to increases in cholesterol screening and flu vaccinations, both considered high-value services. But it also led to increases in low-value care: antibiotic prescriptions for upper respiratory infections jumped by about 24 percent and X-rays for back pain increased by about 37 percent. Other high-value and low-value services showed no significant change.¹³ In other words, gaining insurance coverage increases the use of medical services broadly, and the system does not always distinguish well between care that helps and care that is unnecessary.

Racial and Ethnic Disparities Under Medicare

Medicare was designed in part to equalize access to health care for older Americans, but significant disparities persist across racial and ethnic lines. After adjusting for other factors, minority beneficiaries had meaningfully lower rates of access across several measures compared to White beneficiaries: about 4.7 percentage points lower for having a primary care clinician as a usual source of care, nearly 11 percentage points lower for specialist visits, about 4.3 points lower for flu vaccinations, and about 6.4 points lower for pneumonia vaccinations.¹⁴ These gaps existed across both traditional Medicare and Medicare Advantage, suggesting that simply having insurance coverage does not erase barriers related to provider availability, geography, language, trust, or structural racism.

People Who Qualify for Both Medicare and Medicaid

About 12 million Americans are “dual-eligible,” meaning they qualify for both Medicare and Medicaid. These are typically people who are 65 or older (or disabled) and have very low incomes. Medicaid helps cover premiums, deductibles, and copays that Medicare leaves behind, and it also covers services Medicare does not, particularly long-term care in nursing facilities.

Dual-eligible beneficiaries account for a disproportionate share of spending in both programs. Among those classified as high-cost, more than half remained high-cost across all three years of one observational study, spending an average of about $161,000 per year compared with roughly $22,000 for non-high-cost dual-eligible beneficiaries. Most of that spending among persistently high-cost patients, about 69 percent, went to long-term care, while less than 1 percent was related to potentially preventable hospitalizations.¹⁵ The persistently high-cost group tended to be younger and had greater intellectual impairment, suggesting that much of the spending reflects long-term support needs rather than acute medical crises that could be prevented through better outpatient care.

Coordinating care for dual-eligible people is one of the hardest problems in the system. Medicare and Medicaid are run by different entities with different rules, different payment structures, and different data systems. These structural mismatches create confusion for beneficiaries and inefficiency in care delivery.¹⁶

Accountable Care Organizations and Reform Efforts

Medicare has been experimenting with new payment and delivery models designed to improve value, meaning better outcomes for less spending. The most prominent are Accountable Care Organizations (ACOs), groups of doctors, hospitals, and other providers who agree to take shared responsibility for the quality and cost of care delivered to a defined population of Medicare beneficiaries.

Early results from the Pioneer ACO program, which launched in 2012, showed modest but real effects. Beneficiaries in Pioneer ACOs saw smaller increases in total Medicare spending compared to the general fee-for-service population, amounting to aggregate reductions of about $280 million in the first year and $105 million in the second. Inpatient spending accounted for the largest share of savings. ACO-aligned beneficiaries also reported higher satisfaction scores for timely care and clinician communication than both traditional Medicare and Medicare Advantage beneficiaries.¹⁷ Pioneer ACOs also reduced the use of low-value services by about 2 percent and spending on those services by about 4.5 percent in the first year.¹⁸

That said, progress has been uneven. Only about 18 percent of ACOs achieved top-tier value scores in a broader assessment, and on average, ACOs have the potential to improve their care delivery value by about 24 percent based on how efficiently they use resources to generate quality outcomes.¹⁹ ACOs represent a genuine shift away from paying doctors for each individual service and toward paying for results, but the transformation is slow and the savings modest compared with the scale of Medicare spending.

How Medicare Is Funded and Why Solvency Keeps Making Headlines

Medicare Part A is funded primarily through payroll taxes: employees and employers each pay 1.45 percent of wages, and higher earners pay an additional 0.9 percent. This money flows into the Hospital Insurance Trust Fund. Parts B and D are funded through a combination of beneficiary premiums and general federal revenue, meaning they draw from the same tax pool as everything else the government spends money on.

The solvency of the Part A trust fund is a perennial concern. Trustees project when the fund will be depleted based on assumptions about cost growth, enrollment trends, and economic conditions. Historically, major policy reforms have had the biggest impact on extending the fund’s life. An analysis of Trustees Reports from 1985 to 2024 found that laws like the 1984 Deficit Reduction Act, the 1997 Balanced Budget Act, and the 2010 Affordable Care Act produced larger and more sustained solvency extensions than annual tweaks to cost growth assumptions. These reforms worked by directly constraining provider payments and indirectly slowing growth in other parts of the program, including payments to private health plans.²⁰

When you hear that Medicare is “going bankrupt,” the reality is more nuanced. Trust fund depletion would not mean Medicare ceases to exist. Payroll taxes would still come in and cover a large share of Part A costs. What it would mean, absent legislative action, is that payments to hospitals and other Part A providers would need to be reduced to match incoming revenue. Congress has consistently acted before reaching that point, though the political fights over how to do it are rarely pretty.

Telehealth and Recent Coverage Expansions

Before the COVID-19 pandemic, Medicare’s telehealth coverage was narrow, limited mostly to beneficiaries in rural areas visiting approved provider sites. The pandemic forced a rapid expansion: Medicare temporarily allowed telehealth visits from home, covered audio-only phone visits, and permitted a much wider range of services to be delivered remotely. These flexibilities proved popular with both patients and providers, and Congress has extended them several times rather than letting them expire.

The debate now centers on whether to make these expansions permanent and what the cost implications are. Telehealth clearly improves access for people who have mobility issues, live far from specialists, or need mental health care in a setting where they are comfortable. But broader access also means more utilization, and policymakers are weighing whether the additional spending reflects care that was previously going unmet or care that would not have been sought otherwise. Mental health services have seen particularly strong uptake via telehealth among Medicare beneficiaries, filling a gap in a population where mental health needs are common but historically underserved.

Medicare’s coverage rules around telehealth remain a moving target, subject to short-term legislative extensions rather than settled permanent policy. If you rely on telehealth for ongoing care, it is worth checking annually whether the specific flexibilities you depend on have been renewed.