Medicare Coverage Explained: What Seniors Actually Get in 2025

The Four-Part Framework

Medicare is administered by the Centers for Medicare & Medicaid Services (CMS) and funded jointly through payroll taxes, federal general revenue, and beneficiary premiums. The program is structured around four labeled components — Parts A, B, C, and D — each covering a different category of care. Understanding what each Part does and does not cover is the foundation for every enrollment and plan decision you will make.

Parts A and B together constitute "Original Medicare," the government-run baseline that has existed since 1965. Parts C and D are layered on top and involve private insurers under contract with CMS. Choosing between Original Medicare plus supplemental coverage and a Medicare Advantage plan is the central decision that shapes all the others — and it is one most people make under-informed.

Part A: Hospital Insurance

Most beneficiaries receive Part A premium-free, provided they or their spouse paid Medicare payroll taxes for at least 40 calendar quarters (10 years of covered employment). Those with 30 to 39 quarters pay a reduced premium, and those with fewer than 30 quarters pay the full 2025 premium of $518 per month — a detail that surprises some immigrants and non-traditional workers who spent significant portions of their careers outside the covered payroll system.

What Part A Covers

• Inpatient hospital stays in a semi-private room, meals, general nursing, and drugs administered during the stay
• Skilled nursing facility (SNF) care following a qualifying hospital stay of at least three days, subject to specific day-based cost-sharing rules
• Home health care when ordered by a physician and provided by a Medicare-certified agency
• Hospice care for beneficiaries with a terminal prognosis of six months or fewer, certified by two physicians
• Inpatient psychiatric care with a lifetime cap of 190 days in a freestanding psychiatric hospital

Part A Cost-Sharing in 2025

The inpatient deductible in 2025 is $1,676 per benefit period — not per calendar year, but per spell of illness. A benefit period begins when you are admitted and ends when you have been out of a hospital or SNF for 60 consecutive days. You can technically face this deductible multiple times in a year if you recover, return home, and are readmitted after 60 days. Days 1 through 60 carry no daily coinsurance after the deductible. Days 61 through 90 cost $419 per day. Days 91 onward draw from a 60-day "lifetime reserve," at $838 per day. Once those 60 reserve days are spent, they do not replenish.

For skilled nursing facilities, the first 20 days of a covered SNF stay carry no coinsurance. Days 21 through 100 cost $209.50 per day. Beyond day 100, Medicare pays nothing. The financial exposure in a prolonged SNF stay is one of the most commonly underestimated retirement healthcare risks. According to Medicaid.gov, Medicaid eventually covers long-term nursing home costs for those who have spent down assets to eligibility thresholds — a planning consideration worth discussing with an elder law attorney well before a crisis occurs.

Part B: Medical Insurance

Part B carries a standard monthly premium of $185.00 in 2025, deducted automatically from Social Security benefit payments for most beneficiaries. The annual deductible is $257, after which Medicare pays 80 percent of approved charges and you pay the remaining 20 percent — without any out-of-pocket maximum under Original Medicare alone.

What Part B Covers

• Physician services including surgery, consultation, and second opinions
• Outpatient hospital care including emergency room visits that do not result in admission
• Preventive services such as the Annual Wellness Visit, cardiovascular screenings, colonoscopies, mammograms, Pap tests, prostate screenings, and flu shots — most at 100 percent with no cost-sharing
• Durable medical equipment (DME) including wheelchairs, walkers, blood glucose monitors, and CPAP equipment
• Ambulance services when other transportation would endanger health
• Outpatient mental health services, now covered at the same 80/20 rate as other Part B services following parity law changes
• Physical, occupational, and speech therapy
• Diabetes self-management training and medical nutrition therapy for eligible conditions

The Part B preventive benefit expansion implemented following the Affordable Care Act has added meaningful value for older adults. Annual Wellness Visits do not include a physical examination per se but create a documented baseline, allow you to update your advance directives, and generate a personalized prevention plan — all at no cost-sharing. Many seniors skip this visit because they conflate it with a routine physical, which carries cost-sharing. The distinction matters.

Part C: Medicare Advantage

Medicare Advantage plans, authorized under Part C, are offered by private insurance companies approved by CMS. When you enroll in an MA plan, you receive your Part A and Part B benefits through the private insurer rather than directly through the federal government. In exchange, you typically pay a reduced or $0 monthly premium (on top of your Part B premium, which you continue paying) but agree to use a network of providers.

According to the Kaiser Family Foundation, more than half of all Medicare beneficiaries — roughly 33 million people — were enrolled in Medicare Advantage plans as of 2024, a figure that has grown dramatically over the past decade. The appeal is understandable: most MA plans include Part D drug coverage, many add dental, vision, and hearing benefits not covered under Original Medicare, and the low premium headline number is attractive.

The trade-offs require careful evaluation, however. MA plans almost always involve prior authorization requirements for specialist visits, procedures, and certain medications. Provider networks can change annually, meaning a hospital or physician in your plan's network in January may not be in January of the following year. And while MA plans are required to cap out-of-pocket costs — the maximum out-of-pocket limit for in-network services in 2025 is $9,350 — that ceiling is meaningfully higher than many beneficiaries anticipate.

The 2025 CMS Final Rule implemented significant changes to Medicare Advantage marketing practices and broker compensation structures, aimed at reducing the "churning" of beneficiaries between plans driven by agent financial incentives rather than beneficiary need. These regulatory changes are worth following, as they affect how plans are sold and compared in your area.

Part D: Prescription Drug Coverage

Part D plans, offered by private insurers, cover outpatient prescription drugs. Each plan maintains a formulary — a list of covered drugs organized into tiers — with different cost-sharing amounts at each tier. Generic drugs typically fall into low-cost tiers. Brand-name drugs and specialty medications occupy higher tiers, sometimes with substantial coinsurance percentages.

The most consequential change to Part D in a generation took effect in 2025 under the Inflation Reduction Act: the elimination of the catastrophic coverage phase out-of-pocket threshold has been replaced with a hard $2,000 annual cap on beneficiary Part D spending. For anyone who previously reached the catastrophic coverage threshold, this represents meaningful financial relief. For most beneficiaries on modest drug regimens, the change may have less visible impact — but the structural simplification is significant, and the cap provides genuine protection against the unpredictable cost of newly diagnosed conditions requiring expensive specialty medications.

Choosing a Part D Plan

The Medicare Plan Finder tool at Medicare.gov allows you to enter your specific medications, preferred pharmacy, and zip code to compare actual estimated annual costs across available plans. The monthly premium is rarely the most important variable. A plan with a $0 premium may have a formulary that places your maintenance medications in Tier 3 or Tier 4, generating substantially higher annual out-of-pocket costs than a plan with a $35 monthly premium and Tier 1 or Tier 2 placement for the same drugs.

Income-Related Premium Adjustments (IRMAA)

Beneficiaries with higher incomes pay more for Part B and Part D. The adjustment, called the Income-Related Monthly Adjustment Amount (IRMAA), is based on your modified adjusted gross income from two years prior. This two-year lag creates situations that catch people off guard: a one-time large income event in 2023 — a home sale, a large Roth conversion, or a required minimum distribution from an inherited IRA — will affect your 2025 Medicare premiums.

If your income has dropped significantly since the year used for IRMAA calculation — due to retirement, divorce, death of a spouse, or other life-changing events — you can file Form SSA-44 to request a reconsideration using more recent income data. The Social Security Administration processes these appeals and can adjust your premium prospectively. Managing retirement account distributions with IRMAA thresholds in mind is now a standard element of comprehensive retirement income planning. See our guide on retirement savings strategies for additional context on tax-efficient withdrawals.

Enrollment Windows and Penalties

Medicare's enrollment system is organized around several distinct windows, and missing the right one carries permanent financial consequences that many people do not discover until their first premium bill.

Initial Enrollment Period (IEP)

The IEP runs for seven months: the three months before your 65th birthday month, your birthday month itself, and the three months after. Enrolling in Part B during the first three months — before your birthday month — ensures coverage begins on the first day of your birthday month. Waiting until the birthday month itself or afterward delays coverage start and may affect IRMAA calculations. If you delay enrollment in Part B past your IEP without a qualifying Special Enrollment Period, you will pay a 10 percent premium surcharge for each full 12-month period you were eligible but not enrolled — permanently.

Special Enrollment Period (SEP)

If you or your spouse has active employer-sponsored health coverage when you turn 65, you may delay Part B enrollment without penalty. The SEP allows you to enroll within eight months of losing that employer coverage. "COBRA coverage" and "retiree health benefits" do not qualify as active employer coverage for this purpose — a distinction that has trapped many retirees. Once COBRA begins, the eight-month SEP clock does not pause or restart. According to HHS Administration for Community Living, confusion about SEP qualifying conditions is one of the most common reasons older adults inadvertently accumulate late enrollment penalties.

Annual Enrollment Period (AEP)

Each year from October 15 through December 7, beneficiaries may switch between Original Medicare and Medicare Advantage, change Medicare Advantage plans, or add, change, or drop Part D coverage. Changes made during AEP take effect January 1 of the following year. This is the window to use the Medicare Plan Finder to review whether your current plan's formulary still covers your medications at the same tier, whether your providers are still in-network, and whether a different plan would reduce your total annual costs.

What Medicare Does Not Cover

The coverage gaps in Medicare are extensive enough to warrant their own commentary, but the most financially significant areas are worth highlighting explicitly.

• Routine dental care: cleanings, fillings, extractions, bridges, and most dentures are excluded from Original Medicare. This gap represents a major out-of-pocket expense for many older adults. A 2023 analysis from the Commonwealth Fund found that 40 percent of Medicare beneficiaries had not visited a dentist in the prior year, with cost cited as the primary barrier.
• Routine vision care: eye exams for glasses or contact lenses, most eyeglasses, and most contact lenses are not covered. Medically necessary treatment for conditions like glaucoma and cataracts is covered under Part B.
• Hearing aids and routine hearing exams: not covered under Original Medicare, despite hearing loss being one of the most prevalent conditions affecting adults over 65. The untreated hearing loss connection to cognitive decline has added urgency to this coverage gap in recent policy discussions.
• Long-term custodial care: nursing home care, assisted living, and home aide services that assist with activities of daily living are not covered by Medicare when skilled care is no longer required. This is the coverage gap most likely to consume retirement assets and most often misunderstood. See our related guide on retirement mistakes to avoid for a broader discussion of long-term care planning.
• Most care outside the United States: with narrow exceptions in border regions and emergencies, Original Medicare does not cover care received abroad. Travelers should look into supplemental travel health insurance. Our senior travel insurance guide covers this topic in detail.
• Cosmetic surgery, acupuncture (with exceptions), and most routine foot care

Medigap Supplemental Plans

Medigap (also called Medicare Supplement) policies are sold by private insurers to fill the cost-sharing gaps in Original Medicare. Standardized by federal law into lettered plan types (A through N), Medigap plans must provide the same core benefits regardless of which insurer sells them, though premiums vary significantly between carriers and by location.

Plan G is currently the most comprehensive option available to new enrollees (Plan F, which also covered the Part B deductible, is no longer available to those who became Medicare-eligible after January 1, 2020). Plan G covers the Part A deductible, all Part A coinsurance, Part B coinsurance, foreign travel emergency care, and skilled nursing facility coinsurance — leaving only the Part B deductible ($257 in 2025) as a remaining out-of-pocket cost.

The critical enrollment consideration: Medigap plans sold during your Initial Enrollment Period (the six-month window starting the month you turn 65 and enroll in Part B) are guaranteed-issue — insurers cannot deny coverage or charge higher premiums based on health status. Outside that window, medical underwriting applies in most states, and pre-existing conditions can result in coverage denials or prohibitive premiums. This open enrollment window closes permanently, making the initial enrollment period for Medigap one of the most consequential and least publicized deadlines in healthcare planning for older adults.

Key Decisions Before Enrolling

The structural complexity of Medicare means that the "right" set of choices depends heavily on individual circumstances — current health status, anticipated healthcare needs, income trajectory, provider relationships, travel patterns, and risk tolerance. That said, several questions consistently separate informed decisions from regretted ones.

Original Medicare vs. Medicare Advantage: The Core Trade-Off

Original Medicare plus Medigap provides predictable cost-sharing and unrestricted provider access nationwide — valuable if you see specialists at major academic medical centers, split time between states, or want to avoid network restrictions during a complex illness. The total monthly premium cost is higher, but the out-of-pocket exposure is capped and predictable.

Medicare Advantage typically offers lower visible premium costs and bundled benefits, but introduces network constraints, prior authorization requirements, and annual plan changes that can disrupt established care relationships. The lower monthly cost can be illusory for high-utilization enrollees who encounter authorization denials or out-of-network charges.

If you are currently healthy and your primary concern is premium cost, MA may look more appealing. If you have complex or chronic conditions, strong relationships with specific providers, or significant travel plans, Original Medicare with Medigap typically provides more stable and predictable coverage. The University of Michigan Health Policy program has published research suggesting that higher-need beneficiaries experience better outcomes under Original Medicare, while lower-need beneficiaries do comparably well under either model.

Don't Optimize for Monthly Premium Alone

The single most common enrollment mistake is selecting a plan based primarily on its monthly premium. Total annual cost — premiums plus deductibles, copays, coinsurance, and medication costs — is the correct variable to optimize. A plan with a $0 monthly premium can easily cost more than a plan with a $150 premium once your actual utilization pattern is applied to each plan's cost-sharing structure.

Review Annually During AEP

Medicare plan features are not static. Formularies change, provider networks change, and your health needs change. Setting aside an hour each October to run your medications through the Medicare Plan Finder and confirm your providers are still in-network is one of the highest-return actions available to Medicare beneficiaries. For more on managing the broader financial picture, our guide on retirement financial planning offers additional perspective.