Original Medicare Explained: How Parts A and B Work Together

"Original Medicare" is the federal health insurance program that's been around since 1966. It consists of two parts — Part A (hospital insurance) and Part B (medical insurance) — administered directly by the federal government through the Centers for Medicare & Medicaid Services (CMS). When people say "Medicare" without any qualifier, they usually mean Original Medicare.

The term matters because it distinguishes the government-run program from Medicare Advantage (Part C), which is private insurance that replaces the way Original Medicare benefits are delivered. Your parent's first major Medicare decision is whether to stay with Original Medicare or switch to Medicare Advantage — and that decision affects everything from which doctors they can see to how much a hospital stay will cost.

This article explains how Original Medicare works on its own, what it covers, what it leaves out, and why most people who choose Original Medicare also need supplemental coverage.

How Original Medicare is structured

Part A: hospital insurance

Part A covers inpatient services — the care your parent receives when formally admitted to a hospital, a skilled nursing facility, or hospice. The key services include:

• Inpatient hospital stays (semi-private room, nursing, meals, drugs, lab tests)
• Skilled nursing facility care (up to 100 days per benefit period, after a qualifying 3-day hospital stay)
• Hospice care (comfort care for terminal illness)
• Some home health services (intermittent skilled nursing and therapy)

Most people pay $0/month for Part A because they paid Medicare taxes for at least 10 years during their working life.

Part A has a per-benefit-period deductible of $1,676 in 2026. A benefit period starts with hospital admission and ends after 60 consecutive days without inpatient care. If your parent is hospitalized, discharged, and readmitted within 60 days, it's the same benefit period. If readmitted after 60+ days, a new benefit period starts and the deductible applies again.

Part B: medical insurance

Part B covers outpatient services — doctor visits, lab tests, outpatient surgery, preventive screenings, medical equipment, ambulance services, and mental health care. It also covers drugs administered in a clinical setting (such as chemotherapy infusions).

Part B costs $185/month in 2026 (higher for people with income above $106,000, due to IRMAA surcharges). After a $257 annual deductible, your parent pays 20% of the Medicare-approved amount for most services. Medicare pays the other 80%.

The critical issue: Original Medicare Part B has no annual out-of-pocket maximum. That 20% coinsurance has no cap. In a year with major medical expenses — cancer treatment, extensive surgery, ongoing therapy — the 20% can accumulate to tens of thousands of dollars.

How Original Medicare works in practice

Seeing doctors

With Original Medicare, your parent can see any doctor, specialist, or hospital in the entire country that accepts Medicare. There's no network. They don't need a referral to see a specialist. They don't need prior authorization for most services.

Over 97% of non-pediatric physicians in the United States accept Medicare. This near-universal provider acceptance is the biggest practical advantage of Original Medicare over Medicare Advantage, where your parent is restricted to the plan's network.

How claims are processed

When your parent sees a doctor or receives care:

1. The provider bills Medicare directly
2. Medicare processes the claim and pays its share (80% for most Part B services after the deductible)
3. Your parent receives a Medicare Summary Notice (MSN) every three months showing the services billed, what Medicare paid, and what they owe
4. If your parent has a Medigap plan, the remaining balance is automatically sent to the Medigap insurer for payment

Your parent doesn't typically have to submit claims themselves. The provider handles the billing. If your parent has Medigap, many plans have "crossover" agreements with Medicare — meaning the claim automatically flows from Medicare to the Medigap plan without any action needed.

What Original Medicare doesn't cover

These gaps are consistent and significant:

• Prescription drugs — Original Medicare does not cover medications taken at home. Your parent needs a separate Part D plan.
• Dental care — cleanings, fillings, extractions, dentures
• Vision care — routine eye exams, glasses, contact lenses
• Hearing aids — and routine hearing exams
• Long-term care — nursing home stays (beyond skilled nursing), assisted living, custodial care
• Care outside the US — with very limited emergency exceptions

These gaps mean that Original Medicare alone is not complete health coverage. Most people supplement it with additional plans.

What most people add to Original Medicare

Medigap (Medicare Supplement insurance)

A Medigap plan covers the cost-sharing gaps — the deductibles, coinsurance, and copayments that Original Medicare leaves to your parent. The most popular option, Plan G, covers everything except the $257 Part B deductible. With Plan G, your parent's total annual out-of-pocket for Medicare-covered services is $257, regardless of how much care they receive.

Medigap plans are sold by private insurance companies, but the benefits are federally standardized. A Plan G from one company covers the same benefits as a Plan G from any other company. Monthly premiums typically range from $120-$300 depending on age, location, and insurer.

Medigap plans cannot be combined with Medicare Advantage. It's one path or the other.

Part D (prescription drug coverage)

Part D plans cover prescription medications and are sold by private insurers. Premiums average $40-$55/month, and in 2026, total out-of-pocket drug costs are capped at $2,000/year under the Inflation Reduction Act.

Your parent chooses a Part D plan based on whether it covers their specific medications at their preferred pharmacy at a reasonable cost. Plan formularies (the list of covered drugs) and pricing vary significantly between plans — the same drug can be $10/month on one plan and $80/month on another.

The complete Original Medicare setup

The most common configuration for people who choose Original Medicare is:

Original Medicare (A + B) + Medigap Plan G + Part D drug plan

This provides:

• Hospital and medical coverage with virtually no cost-sharing risk
• Any doctor in the country, no network, no referrals
• Prescription drug coverage with a $2,000 annual cap
• Predictable monthly costs

What it doesn't provide: dental, vision, hearing, or long-term care. These require separate policies or out-of-pocket payment.

Original Medicare vs. Medicare Advantage

This is the fundamental fork in the road for every Medicare enrollee. Here's the honest comparison:

Original Medicare wins on: provider freedom, predictable costs (with Medigap), no prior authorization hassles, nationwide portability.

Medicare Advantage wins on: lower monthly premiums, bundled dental/vision/hearing, simpler single-card coverage, built-in out-of-pocket cap without needing Medigap.

Neither is universally better. The right choice depends on your parent's health, budget, location, and how they use healthcare.

Who should choose Original Medicare

Original Medicare with a Medigap supplement tends to be the stronger choice for parents who:

• Have chronic conditions requiring ongoing specialist care — no network restrictions means uninterrupted access to their preferred doctors
• Are dealing with or at risk for serious illness (cancer, heart disease) — no prior authorization delays for treatment
• Travel frequently or split time between states — coverage works the same everywhere
• Prioritize predictable costs over the lowest premium — Medigap eliminates financial uncertainty
• Value the ability to see any doctor, anywhere, without asking permission

For families managing a parent's Medicare, the simplicity of "any doctor, any hospital, and Medigap covers the rest" can also reduce the administrative burden considerably compared to navigating Advantage plan networks and prior authorizations.

Our Medicare Enrollment Guide walks through the Original Medicare setup step by step — including how to pair the right Medigap plan with the right Part D plan, a provider freedom comparison worksheet, and the enrollment timeline for getting everything in place without gaps in coverage.