Medicare Part A vs. Part B: What's the Difference and What's Covered

Medicare has two foundational parts, and understanding how they divide up coverage is essential before you can make sense of the rest of the program. Part A and Part B serve different purposes, carry different costs, and fill different gaps in your care. Here's how each one works — and what factors determine how much they'll matter to you.

The Simple Version: Hospital vs. Medical 🏥

The easiest way to start is with a broad distinction:

• Medicare Part A is your hospital insurance. It covers care you receive as an inpatient — when you're admitted to a facility for treatment.
• Medicare Part B is your medical insurance. It covers the services and supplies you need to diagnose and treat conditions — mostly on an outpatient basis.

Both parts together make up what's often called Original Medicare, the federal program administered directly by the government. Most people who enroll in Medicare get both.

What Medicare Part A Covers

Part A focuses on institutional care — situations where you're receiving treatment inside a facility rather than visiting a doctor's office.

Core Part A coverage typically includes:

• Inpatient hospital stays — semi-private room, meals, nursing care, and most hospital services and supplies during an admitted stay
• Skilled nursing facility (SNF) care — but only under specific conditions, including a qualifying hospital stay of a minimum number of days beforehand
• Home health care — certain medically necessary skilled nursing or therapy services delivered at home
• Hospice care — for individuals with a terminal prognosis who choose comfort-focused care

What Part A does not cover: routine physician visits, outpatient procedures, prescription drugs, dental, vision, or most preventive screenings. Those fall under Part B or other coverage.

The Part A Cost Structure

Most people pay no monthly premium for Part A if they or their spouse worked and paid Medicare taxes for a sufficient number of years (generally a decade or more of work). This is often described as having "paid into" Medicare.

People who don't meet that work history threshold can still enroll in Part A but may pay a monthly premium — and that premium can vary depending on how many quarters of Medicare taxes they paid.

Part A does, however, carry cost-sharing. There's a deductible per benefit period (not per year), and there are coinsurance charges that kick in after an extended inpatient stay. The exact figures change annually, so always verify current amounts through Medicare.gov or your benefits materials.

What Medicare Part B Covers

Part B is broader in some ways — it's the part that handles the ongoing medical care most people use more regularly.

Core Part B coverage typically includes:

• Doctor visits — primary care, specialists, and second opinions
• Outpatient surgery and procedures — care you receive without a formal hospital admission
• Preventive services — screenings, vaccines, and annual wellness visits (often at no cost-sharing when provided by a participating provider)
• Durable medical equipment (DME) — items like wheelchairs, walkers, blood sugar monitors
• Mental health services — outpatient therapy and psychiatry
• Ambulance services — when medically necessary
• Some home health care — similar to Part A, for qualifying situations
• Certain outpatient drugs — including drugs administered in a clinical setting, like chemotherapy or injections

What Part B does not cover: most prescription drugs you take at home (that's Part D), long-term custodial care, most dental and vision, and hearing aids.

The Part B Cost Structure

Unlike Part A, Part B always comes with a monthly premium. The standard premium amount is set annually by the federal government and applies to most enrollees. However, individuals with higher incomes pay more through what's called IRMAA (Income-Related Monthly Adjustment Amount) — a surcharge based on your reported income from two years prior.

Part B also includes an annual deductible and typically requires 20% coinsurance for most covered services after you meet the deductible — with no out-of-pocket maximum under Original Medicare alone. That open-ended cost exposure is one reason many people supplement Original Medicare with Medigap or Medicare Advantage coverage.

Part A vs. Part B: Side-by-Side 📋

When the Line Between Part A and Part B Gets Blurry

One area that trips people up: hospital outpatient status vs. inpatient admission.

If you're in a hospital but haven't been formally admitted — you're under "observation status" — your care may be billed under Part B, not Part A. That distinction matters significantly, because Part A inpatient rules and Part B outpatient rules carry different cost-sharing structures and different implications for skilled nursing facility eligibility afterward.

This is a genuine gap in consumer awareness. If you or a family member is in a hospital setting for more than a day or two, it's worth asking directly whether you've been formally admitted or placed under observation.

What Determines How These Parts Affect You 🔍

Neither part works identically for every person. Several factors shape your experience:

• Your work history — determines whether you qualify for premium-free Part A
• Your income — affects Part B premium amounts through IRMAA
• Whether you have other coverage — employer coverage, retiree benefits, or a spouse's plan may change when and how you enroll without penalty
• Your health utilization — people with more frequent inpatient stays will feel Part A's cost structure differently than those who primarily use outpatient services
• Whether you enroll in a supplement — Medigap plans or Medicare Advantage change what you actually pay out of pocket beyond Original Medicare

Enrollment: The Basics

Most people are automatically enrolled in both Part A and Part B when they turn 65 if they're already receiving Social Security benefits. Others need to actively enroll during their Initial Enrollment Period — a window around their 65th birthday.

Delaying Part B is sometimes appropriate — particularly for people still covered by employer insurance through active employment. But delaying without a qualifying reason can trigger permanent late enrollment penalties that increase your premium for as long as you have Part B. The rules around this are specific and consequential enough that it's worth reviewing them carefully before making any decision.

What You'd Need to Evaluate for Your Own Situation

Understanding what Part A and Part B cover is just the foundation. What matters next is how that coverage fits your specific circumstances: your health needs, your financial situation, your existing coverage, your providers, and your timeline for retirement. Original Medicare leaves meaningful gaps — no prescription drug coverage, no out-of-pocket maximum, limited dental and vision — and how you address those gaps depends entirely on trade-offs that vary by person.

Medicare.gov is the authoritative source for current costs, enrollment windows, and coverage details. A State Health Insurance Assistance Program (SHIP) counselor can provide free, unbiased guidance tailored to your specific situation.