Original Medicare, the unbundled federal program

Original Medicare is the federal program run directly by the Centers for Medicare & Medicaid Services (CMS). It has two parts.

Part A, hospital insurance. Covers inpatient hospital stays, skilled nursing facility care, hospice, and limited home health.

Part B, medical insurance. Covers doctor visits, outpatient services, preventive care, durable medical equipment, lab and imaging, and some mental health.

That’s it. Original Medicare does not include prescription drugs, routine dental, routine vision, hearing aids, or long-term custodial care. You add prescription coverage through a separate Part D plan, and you cover the 20% of Part B that Original doesn’t pay through a Medigap supplement, or you absorb the risk yourself.

The structural distinction from Medicare Advantage: with Original Medicare, any provider who accepts Medicare assignment (most do) is "in-network" for you. There’s no referral required for most specialists, no prior authorization for most services, no county-scoped network that drops off the moment you cross a state line. Your Medicare card is your only ID; the system processes claims behind the scenes.

Part A is what kicks in when you’re admitted to a hospital, skilled nursing facility, or hospice. For most people it’s free: if you or your spouse worked at least 40 quarters (10 years) paying Medicare taxes, your Part A premium is $0/month.

What Part A covers.

• Inpatient hospital stays. Semi-private room, meals, general nursing, drugs administered while you’re inpatient, and most hospital services. Days 1 to 60 of a benefit period: you pay the $1,736 inpatient deductible, Medicare covers the rest. Days 61 to 90: $434/day coinsurance. Days 91+: $868/day drawn from a 60-day lifetime reserve pool (then you pay all costs).
• Skilled nursing facility (SNF) care. Only after a qualifying 3-day inpatient hospital stay. Days 1 to 20: $0. Days 21 to 100: $217/day coinsurance. Day 101+: all costs are on you. This is skilled nursing, physical therapy after a fall, IV antibiotics, wound care. It is not custodial care.
• Hospice. For terminally ill patients with a 6-month-or-less prognosis. Original Medicare covers it; copays are minimal or zero.
• Home health. Only if you’re homebound and need part-time skilled nursing or therapy, ordered by a doctor. Narrow.

What Part A doesn’t cover. Long-term custodial nursing-home care, the kind where you need help with daily activities but don’t need skilled medical care. This is the single biggest Medicare misconception. Long-term custodial care is on you, or on Medicaid if you spend down enough assets to qualify.

If you haven’t worked 40 quarters paying Medicare taxes, Part A costs $311/mo (30 to 39 quarters) or $565/mo (less than 30 quarters) in 2026. Most enrollees never see this; auto-enrollment and the 40-quarter threshold cover the typical case.

Part B is what you use day-to-day. It’s not free: the standard 2026 premium is $202.90/month, deducted from your Social Security check if you receive one. The annual deductible is $283.

After your deductible, Part B pays 80% of approved charges for a wide list of services:

• Doctor visits, primary care, specialists, telehealth.
• Outpatient hospital care, same-day surgeries, ER visits not resulting in admission.
• Preventive services, annual wellness visit, flu shot, cancer screenings, diabetes prevention. No deductible applies to covered preventive services.
• Mental health, outpatient therapy, psychiatric medication management.
• Durable medical equipment, wheelchairs, walkers, oxygen, CPAP machines.
• Ambulance, when medically necessary, ground or air.
• Lab tests, X-rays, MRIs, and most imaging.
• Physical, occupational, and speech-language therapy.
• Limited dental in narrow medical circumstances (e.g., dental needed before cardiac surgery).
• Limited vision (eye exam if you’re diabetic high-risk, post-cataract glasses).

You pay the remaining 20% with no annual cap. That uncapped 20% is the structural reason most Original Medicare enrollees add a Medigap policy.

Here’s the math that catches new enrollees off guard: Part B pays 80% of approved charges, you pay 20%, and there is no annual cap on your 20%.

A typical year: a few doctor visits, some lab work, maybe one outpatient procedure. Your 20% adds up to maybe $800 to $1,500. Manageable.

A bad year: a serious hospital stay (Part A deductible: $1,736), then weeks of outpatient rehab and follow-up care under Part B. The Part B 20% on $50,000 of approved charges is $10,000. Plus Part A coinsurance if your hospital stay went past day 60. The bad year ends with $12,000 to $20,000+ out of pocket. There’s no cap.

This is why Original Medicare enrollees almost always add a Medigap (Medicare Supplement) policy. Medigap is sold by private carriers, but the plans are standardized by letter, a Plan G from one carrier covers exactly what a Plan G from another carrier covers. The only thing that varies between carriers is the price.

The two most common Medigap plans in 2026:

• Plan G. Covers everything Original Medicare doesn’t except the Part B annual deductible. A 65-year-old non-smoker pays roughly $130 to $180/month in most states.
• Plan N. Slightly lower premium than Plan G, with small office-visit and ER copays plus a few uncovered items (excess charges, the Part B deductible).

Plan F, the most comprehensive plan, is closed to new enrollees who became Medicare-eligible after January 1, 2020 (per MACRA, 2015). If you were eligible before that date, you can still buy or keep it.

The critical timing rule: you get a 6-month Medigap Open Enrollment window starting the month you turn 65 and have Part B. During that window, no carrier can deny you coverage or charge you more based on health history. After that window, in most states, they can, and they do.

Three paths to eligibility.

• Age 65. You become eligible the first day of the month you turn 65. If you’re receiving Social Security retirement benefits, you’re auto-enrolled, your card arrives in the mail. If you’re not yet receiving Social Security, you have to apply manually through SSA.
• Disability. After 24 months of SSDI benefits, you become eligible regardless of age.
• ESRD or ALS. End-stage renal disease and amyotrophic lateral sclerosis trigger immediate eligibility without the 24-month wait.

The 7-month Initial Enrollment Period (IEP).

• The three months before your 65th-birthday month, coverage starts the first day of your birthday month.
• Your birthday month, coverage starts the first day of the following month.
• The three months after your birthday month, coverage starts after a delay.

How to sign up. Online through Social Security at ssa.gov, by phone at 1-800-772-1213, or in person at a Social Security office. If you’re already on Social Security retirement benefits, you’re auto-enrolled in both Part A and Part B; you can decline Part B if you have credible employer coverage. If you’re not yet on Social Security, you have to actively enroll, Medicare won’t sign you up for you.

Missing your IEP costs real money. Part B carries a permanent 10% late-enrollment penalty for every full 12-month period you delayed without credible coverage. Part D adds 1% per month of delay. Both penalties stick to your premium for as long as you have Medicare.

The exception that matters. If you’re still working at 65 and have credible employer coverage through a company with 20 or more employees, you can defer Part B without penalty and enroll later through a Special Enrollment Period (SEP). The SEP runs 8 months from the end of your employment or coverage. COBRA and retiree coverage do not count as credible for SEP purposes, sign up for Part B before COBRA starts, not after.

These gaps are why Medicare can feel surprisingly thin to new enrollees.

• Prescription drugs, except a few administered in a doctor’s office or hospital. You add a Part D plan separately ($0 to $60/mo typical range, plus copays per drug).
• Routine dental, cleanings, fillings, crowns, dentures. Limited exception for dental needed before a covered surgery. You add a standalone dental policy or rely on Medicare Advantage’s bundled dental benefit.
• Routine vision, eye exams, glasses, contacts. Narrow exception for medically necessary cases (high-risk diabetics, post-cataract surgery glasses).
• Hearing, exams, aids, fittings. Generally not covered by Original Medicare; Medicare Advantage often bundles a hearing benefit with annual allowance.
• Long-term custodial care, see Part A above. This is the big one.
• Routine care outside the U.S., Medicare doesn’t follow you abroad, with narrow exceptions (Canada/Mexico in emergencies, U.S.-flagged ships within 6 hours of a U.S. port). If you travel, Medigap Plan G’s foreign travel emergency benefit fills part of this gap.
• Cosmetic surgery, weight-loss programs (with narrow exceptions for medically necessary bariatric surgery), acupuncture (limited coverage for chronic low back pain only), and most chiropractic care (only spinal manipulation for subluxation).

If a service feels like it should be covered but you’re not sure, the medicare.gov "What’s covered" search is the authoritative source.

The honest comparison, framed as the four questions that actually decide which path is right.

1. Do you want to see any doctor, anywhere? Original wins. With Original Medicare, any provider who accepts Medicare assignment (the vast majority do) is in-network. No referrals required, no prior authorization for most services, no county-scoped network. Medicare Advantage plans have networks, usually county-scoped HMO networks, sometimes regional or national PPO networks. If you travel, see specialists across states, or have strong attachment to a specific doctor who isn’t in the local Advantage networks, Original is the better fit.

2. Do you want predictable monthly cost or a cap on the worst year? Original Medicare gives you predictable monthly cost, Part B premium plus Medigap premium plus Part D premium, but no annual cap on what you pay out of pocket (Medigap fills the cap, effectively). Medicare Advantage gives you a Maximum Out-of-Pocket (MOOP) limit, typically $4,000 to $8,000/year in-network in 2026, that caps your worst case. Advantage often has lower monthly premiums but higher copays per service, so a low-utilization year is cheaper on Advantage and a high-utilization year is closer to the same.

3. Do you want extras bundled in? Medicare Advantage wins. Most Advantage plans include dental, vision, hearing, fitness (SilverSneakers or similar), over-the-counter allowance, sometimes transportation or meal benefits. Original Medicare covers none of this, you’d add standalone policies.

4. Do you want maximum flexibility to switch later? Original wins, but only barely. Once you’re on Medicare Advantage, switching back to Original outside specific windows (AEP, MA-OEP, qualifying SEPs) can be hard, and getting Medigap re-issued without underwriting after your initial 6-month window is even harder. If you start with Original + Medigap, you can switch to Advantage during AEP without restriction. If you start with Advantage, going back is the friction.

The decision isn’t moral, neither path is "better." Original suits travelers, people with specific doctors they want to keep, and people who prefer predictable monthly cost with Medigap covering the variability. Advantage suits people who use mostly local in-network care, value the bundled extras, and prefer a MOOP cap.

A few profiles where Original + Medigap + Part D is almost always the better fit.

• You live in two states, travel internationally regularly, or spend months at a vacation home. Original Medicare works everywhere in the U.S.; Advantage networks generally don’t follow you.
• You have a specialist or treatment team you’re committed to, say, a doctor managing a chronic condition, who isn’t in any local Advantage network.
• You expect a high-utilization year (planned major surgery, ongoing serious condition) and want Medigap to cover the 20% so you can budget cleanly.
• You qualify for guaranteed-issue Medigap (a state with year-round GI rights, a qualifying life event, or you’re in your initial 6-month Medigap Open Enrollment window).
• You’re comfortable paying $300 to $450/mo all-in for the simpler structure and broader access.

When Advantage is often the better fit: you use mostly local in-network care, value the bundled dental/vision/hearing, want a MOOP cap, are comfortable with referrals and prior authorization, and don’t travel much. Both paths are defensible. The wrong move is picking one without understanding the trade-offs.