An older adult man and woman sit at a table with a laptop, a notebook, and some paperwork in front of them.
Learn what original Medicare covers, how Parts A and B work, and what’s not included so you can make informed decisions about your coverage. Photo Credit: iStock.com/Jana Murr

For many people who are turning 65 (or those helping a parent or spouse sort through their choices), Medicare begins with two core building blocks: Medicare Parts A and B. These form what’s known as original Medicare, the traditional federal program that has provided hospital and medical coverage to older adults for six decades.

Despite its long history, it’s not always easy to understand what Parts A and B actually cover, what they don’t, and how the costs work. This overview walks you through the essentials so you can make confident decisions about your coverage.

What is original Medicare?

Original Medicare is the foundation of the Medicare system. It includes:

Together, these two parts cover most inpatient and outpatient medical needs, and both have premium, deductible, and coinsurance costs to consider.

Many people manage with only original Medicare throughout retirement. Others pair it with a private Part D prescription plan or a Medicare Supplement (Medigap) policy to help cover out-of-pocket costs.

Still others choose to switch entirely to a Medicare Advantage (Part C) plan, which is an alternative that covers Part A and Part B and usually includes additional benefits such as prescription drug coverage.

However you design your coverage, understanding Parts A and B is an essential first step. 

Medicare Part A: Hospital insurance

Part A helps pay for care you receive as an inpatient in hospitals or skilled nursing facilities (SNFs), as well as hospice care and some home health care under certain circumstances.

What Part A covers

  • Hospital stays: Part A covers semiprivate rooms, nursing care, meals, medications received during your stay, and services such as lab work or imaging performed while you’re admitted.
  • Skilled nursing facility (SNF) care: After a qualifying three-day inpatient hospital stay, Part A covers rehabilitation care in a skilled nursing facility to help with recovery after surgery, illness, or injury. This care is not the same as long-term custodial care. Part A pays only for medically necessary, short-term rehabilitation.
  • Home health care: If you’re homebound and need part-time or intermittent skilled care, such as nursing or physical therapy, Part A can cover it.
  • Hospice care: For individuals with a terminal illness and a life expectancy of six months or less, Part A covers hospice care focused on comfort, symptom management, and quality of life.

What you pay under Part A: Premiums, deductibles, and coinsurance

If you or your spouse has paid Medicare taxes to the federal government for at least 40 quarters of work (10 years), you’ll usually pay no monthly premium for Part A. However, “free” does not mean everything is covered. Part A has its own deductible and cost-sharing rules.

On the other hand, if you’ve paid Medicare taxes for fewer than 40 quarters, your monthly Part A premium in 2026 will be as follows:

  • For less than 30 quarters: $565.
  • For 30-39 quarters: $311.

Part A coverage is based on benefit periods, not calendar years, which can be a surprise to many new enrollees. A benefit period begins when you are admitted to the hospital and lasts for 60 consecutive days after you are discharged from a hospital or SNF. As a result, you could pay for more than one Part A deductible in a calendar year.

Each benefit period begins with a Part A deductible, which beneficiaries must pay out of pocket before Medicare starts to cover any costs. In 2026, the Part A deductible is $1,736. After the deductible, Part A covers all hospital costs for the first 60 days of an inpatient stay. Beyond that, the daily coinsurance is:

  • Days 61-90: $434.
  • After day 90: $868 (with a maximum of 60 lifetime reserve days).

In a skilled nursing facility (SNF), the first 20 days are covered in full, and coinsurance for days 21 to 100 costs $217 per day in 2026. There is no coverage after day 100.

Even though most people pay no premium for Part A, understanding the potential out-of-pocket costs is key to preparing for a hospital or SNF stay.

Medicare Part B: Medical insurance

Medicare Part B helps cover the everyday medical services that help you stay healthy and manage conditions over time.

What Part B covers

Part B covers medically necessary outpatient services, including:

  • Doctor visits: Whether you’re checking in with your primary care physician or consulting a specialist, Part B helps cover the costs of office visits, consultations, and ongoing monitoring.
  • Preventive care: Part B includes flu shots, COVID-19 vaccinations, mammograms, colonoscopies, and many other screenings recommended for older adults. Most preventive services are covered with no deductible or copayment.
  • Diagnostic tests and imaging: X-rays, MRIs, CT scans, blood work, and other diagnostic tests fall under Part B.
  • Outpatient procedures: Many surgeries that used to require hospital stays, such as cataract removal, are now performed in outpatient settings and may be covered by Part B.
  • Therapies: Doctor-ordered physical therapy, occupational therapy, and speech-language pathology services are included.
  • Durable medical equipment (DME): Items like walkers, wheelchairs, home oxygen, and CPAP machines are covered under Part B.

Costs under Part B

Part B has three main cost components:

  • Monthly premium: Most beneficiaries pay a standard monthly premium of $202.90 in 2026. Higher-income individuals may pay an additional income-related monthly adjustment amount (IRMAA) of between $81.20 and $487 more. This affects around 8% of Medicare beneficiaries.
  • Annual deductible: Before Medicare begins paying its share for most services, you must meet an annual Part B deductible of $283 in 2026.
  • Coinsurance: After the deductible is met, Medicare generally pays 80% of the approved amount for covered services, and you pay the remaining 20%. There is no annual out-of-pocket limit in original Medicare, which is why many people opt to buy a private Medigap policy to help cover some or all of the remaining Part B costs.

What original Medicare doesn’t cover 

Understanding what Parts A and B don’t cover is just as important as knowing what they do. Not covered are: 

  • Routine dental care (cleanings, fillings, dentures).
  • Routine vision care (eye exams, glasses).
  • Hearing aids and exams.
  • Long-term custodial care (help with bathing, dressing, eating, etc.).
  • Most prescription drugs.
  • 100% of the cost of covered services, as there are deductibles and coinsurance for nearly all care.

For prescription drug coverage, original Medicare beneficiaries typically enroll in a private stand-alone Medicare Part D plan. For help with cost-sharing, many choose a Medigap plan. Dental, vision, hearing, and long-term custodial expenses remain the responsibility of the beneficiary. 

When to enroll in Medicare Part A and Part B

Most people enroll in Medicare Parts A and B during their initial enrollment period, a seven-month window surrounding their 65th birthday (three months before, the month of, and three months after).

If you or your spouse is still working and covered by a large employer plan, you may delay Part B enrollment without penalty. Once that employment or coverage ends, an eight-month special enrollment period allows you to sign up without a late fee, counted from the month after coverage ends.

Late-enrollment penalties

Medicare Parts A and B both have late-enrollment penalties if you don’t sign up on time and don’t qualify for an exception.

  • Part A penalty: If you have worked enough quarters and enjoy premium-free Part A, there is no reason not to enroll when you are first eligible, around your 65th birthday. On the other hand, if you must pay a premium for Part A and you delay enrolling, your premium may increase by 10% for twice the number of years you waited. For instance, if you delay two years, your premium increases by 10% for four years.
  • Part B penalty: If you don’t sign up for Part B when first eligible and don’t have qualifying employer coverage, your monthly premium may permanently increase by 10% for each complete 12-month period you delay. This penalty lasts for as long as you have Part B.

These penalties exist because Medicare is designed to be a shared-risk program. Everyone pays in, even if they’re healthy. Not paying in and waiting until you’re older and needing services does not support the system.

Understanding how Medicare Parts A and B work, including what they cover, what they don’t, and what you may pay, gives you a clear foundation as you enroll in Medicare. Although the program can seem complex at first, knowing the basics helps you plan for your care and avoid surprises. With this groundwork, you can approach your Medicare decisions with greater confidence and clarity.