More than 67 million Americans were enrolled in Medicare as of 2025, but calling them a single group misses something important: how they actually receive their coverage differs enormously, and those differences carry real financial and medical consequences. According to data tracked by KFF, the Medicare population is now split across several distinct coverage types — Original Medicare alone, Original Medicare paired with a Medigap supplement, Original Medicare paired with Medicaid, and Medicare Advantage plans that bundle hospital, medical, and often drug coverage into a single private plan. Understanding which bucket you fall into — and what each one means for your wallet and your care — is one of the most consequential decisions you can make as a beneficiary.
Medicare Advantage, also called Part C, has grown to cover approximately half of all Medicare enrollees as of 2025, a milestone that would have seemed unlikely just fifteen years ago when the program covered fewer than one in four beneficiaries. These plans are offered by private insurers approved by the Centers for Medicare & Medicaid Services (CMS) and must cover everything Original Medicare covers, but they typically do so through networks of doctors and hospitals. In 2025, the average Medicare beneficiary had access to roughly 40 Medicare Advantage plan options depending on their county, though that number varies dramatically — urban beneficiaries in counties like Miami-Dade or Los Angeles may see 60 or more choices, while rural beneficiaries in parts of Wyoming or Montana may have fewer than five. Many Medicare Advantage plans carry $0 monthly premiums beyond the standard Part B premium, which is $185.00 per month in 2025, and most include a built-in cap on out-of-pocket costs — the maximum out-of-pocket limit for in-network services in Medicare Advantage plans in 2025 is $9,350, though many plans set their caps lower.
Original Medicare — Parts A and B administered directly by the federal government — remains the foundation for the other half of beneficiaries, but it does not work the same way for everyone who uses it. Under Original Medicare, Part A covers inpatient hospital stays with a deductible of $1,676 per benefit period in 2025, and Part B covers outpatient and physician services with a $257 annual deductible and 20% coinsurance after that. Critically, Original Medicare has no out-of-pocket maximum. A beneficiary who suffers a serious illness — a stroke, cancer, a prolonged hospital stay — could theoretically face tens of thousands of dollars in cost-sharing with no ceiling. That exposure is why many beneficiaries in Original Medicare purchase a Medigap supplemental policy, also called Medicare Supplement Insurance, to cover those gaps.
Medigap plans are sold by private insurers and are standardized by federal law into lettered plan types (Plan G, Plan N, and Plan A are among the most common in 2025). Plan G, currently the most comprehensive option available to new enrollees, covers the Part A deductible, Part B coinsurance, skilled nursing facility coinsurance, and foreign travel emergencies — but does not cover the Part B deductible. Monthly premiums for Plan G vary significantly by age, location, and insurer, ranging from roughly $100 to over $300 per month for a 70-year-old depending on the state. Importantly, Medigap plans do not include prescription drug coverage, so beneficiaries who choose this route typically need to also enroll in a standalone Part D drug plan. The average Part D premium in 2025 is approximately $46 per month, though plans range from under $10 to over $100 depending on the formulary and region.
One of the most significant — and often overlooked — segments of the Medicare population is the roughly 12 to 13 million beneficiaries who qualify for both Medicare and Medicaid, a group known as dual eligibles or dual-eligible beneficiaries. These individuals are among the lowest-income and often the most medically complex people in the program. Medicaid, which is administered jointly by states and the federal government, can pay Medicare premiums, deductibles, and coinsurance on behalf of these beneficiaries, dramatically reducing their out-of-pocket burden. There are several categories of dual eligibility — full dual eligibles receive the most comprehensive assistance, while Qualified Medicare Beneficiaries (QMBs) have their Part A and Part B premiums and cost-sharing covered by Medicaid. Specified Low-Income Medicare Beneficiaries (SLMBs) have only their Part B premium covered. If you think you might qualify — generally, income at or below roughly 100–135% of the federal poverty level depending on the category — your State Health Insurance Assistance Program (SHIP) counselor can help you apply at no cost.
The coverage landscape also varies by age and how someone became eligible for Medicare. About 9 million Medicare beneficiaries qualify through disability rather than age, and they tend to face different challenges — they are younger, more likely to be in Medicare Advantage, and more likely to have chronic conditions that generate high utilization. New Medicare enrollees who are 65 and aging in have a guaranteed-issue window to purchase Medigap without medical underwriting during the six-month period that begins the month they turn 65 and are enrolled in Part B. Miss that window, and insurers in most states can use medical underwriting to charge you more or deny coverage based on health history. Thirteen states — including California, New York, Oregon, and Illinois — have additional protections through birthday rules or continuous guaranteed-issue laws that give beneficiaries ongoing opportunities to switch Medigap plans without underwriting.
For beneficiaries currently in Medicare Advantage who are wondering whether Original Medicare plus a Medigap plan might serve them better, the Annual Enrollment Period (AEP) running October 15 through December 7 each year is the primary window to make that switch, with coverage taking effect January 1. There is also a Medicare Advantage Open Enrollment Period from January 1 through March 31, during which beneficiaries already in a Medicare Advantage plan can switch to a different Medicare Advantage plan or return to Original Medicare — though returning to Original Medicare during this window does not automatically guarantee Medigap access in most states. The decision between Medicare Advantage and Original Medicare plus Medigap is not one-size-fits-all: beneficiaries who travel frequently, see specialists outside a network, or want predictable costs often find Medigap more suitable, while those who want low premiums, dental and vision benefits, and are comfortable with network restrictions may prefer Medicare Advantage.
The bottom line is that your coverage source is not just an administrative detail — it is the architecture of your entire healthcare experience. Knowing whether you have Original Medicare, a supplement, a drug plan, Medicaid assistance, or a bundled Advantage plan tells you what you will pay, where you can go for care, and what protections you have if something goes seriously wrong. Reviewing your coverage annually during the AEP, checking the Medicare Plan Finder at Medicare.gov, or calling 1-800-MEDICARE (1-800-633-4227) can help ensure your current plan still fits your health needs and budget as both your situation and the plans themselves change each year.