Medicare Part A covers hospital and inpatient care, while Part B covers doctor visits, outpatient services, and preventive care. Together, they form what’s known as Original Medicare, the federal health insurance available to most Americans at age 65. Understanding what each part pays for, what it costs, and what it leaves out can save you from unexpected bills.
What Part A Covers
Part A is hospital insurance. It pays for care you receive as an admitted inpatient, including a semi-private room, meals, general nursing, medications administered during your stay, and other hospital services and supplies related to your treatment. If you need surgery, are hospitalized for pneumonia, or have a cardiac event, Part A is the portion of Medicare handling those costs.
Part A also covers three other major categories of care:
- Skilled nursing facility care. After a qualifying hospital stay of at least 3 consecutive inpatient days, Part A covers up to 100 days per benefit period in a skilled nursing facility. Time spent under observation or in the emergency room before formal admission does not count toward those 3 days, which catches many people off guard.
- Home health services. If you’re homebound and need skilled nursing or therapy, Part A covers intermittent home health care.
- Hospice care. When a doctor certifies a life expectancy of 6 months or less, Part A covers comfort-focused end-of-life care at no cost to you. You pay only a small copayment of up to $5 per prescription for pain and symptom management drugs, and up to 5% of the approved amount for inpatient respite care (short stays that give your caregiver a break). Hospice coverage runs in benefit periods: two 90-day periods followed by unlimited 60-day periods, and it can continue beyond 6 months as long as a hospice doctor recertifies the terminal illness.
What Part B Covers
Part B is medical insurance. It picks up where Part A stops, covering the outpatient side of health care: doctor’s office visits, diagnostic tests, outpatient surgeries, ambulance services, durable medical equipment like wheelchairs and oxygen supplies, mental health and substance use disorder treatment, and a limited set of outpatient prescription drugs.
Part B divides its coverage into two broad categories. The first is medically necessary services, meaning anything that meets accepted standards of medical practice to diagnose or treat a condition. The second is preventive services, which are designed to catch illness early or prevent it altogether.
Preventive Services at No Cost
One of Part B’s most valuable features is its preventive care lineup. You pay nothing for most of these services as long as your provider accepts Medicare assignment. The list is extensive:
- Cancer screenings: mammograms, colonoscopies, lung cancer screenings, cervical and vaginal cancer screenings, prostate cancer screenings, and colorectal screening options including stool DNA tests and CT colonography
- Cardiovascular screenings and behavioral therapy for heart disease risk
- Diabetes screenings, self-management training, and the Medicare Diabetes Prevention Program
- Vaccines: flu shots, COVID-19 vaccines, pneumococcal shots, and hepatitis B shots
- Mental health: depression screenings
- Other screenings: HIV, hepatitis B and C, sexually transmitted infections, glaucoma, bone density, alcohol misuse, and abdominal aortic aneurysm
- Counseling: tobacco cessation, obesity behavioral therapy, nutrition therapy
- Wellness visits: a one-time “Welcome to Medicare” visit when you first enroll, plus a yearly wellness visit thereafter
These preventive benefits alone can add up to thousands of dollars in savings each year, particularly the cancer screenings and vaccinations.
What Part A and B Cost in 2025
Most people pay no monthly premium for Part A. You qualify for premium-free Part A if you or your spouse paid Medicare taxes for at least 40 quarters (10 years) of work. If you have between 30 and 39 quarters, the 2025 premium is $285 per month. Fewer than 30 quarters means you’ll pay the full premium of $518 per month.
Part B has a standard monthly premium of $185 in 2025, which applies to most enrollees. Higher-income individuals pay more through an income-related adjustment. The annual Part B deductible is $257. After meeting that deductible, you typically pay 20% of the Medicare-approved amount for most covered services, with no annual out-of-pocket cap. That 20% coinsurance is one reason many people add a Medigap supplemental policy or choose a Medicare Advantage plan.
Enrollment Timeline and Late Penalties
Your Initial Enrollment Period lasts 7 months: it starts 3 months before the month you turn 65, includes your birthday month, and extends 3 months after. If you’re already receiving Social Security benefits, you’ll be enrolled automatically. Otherwise, you need to sign up during this window.
Missing your enrollment period has real consequences. If you delay Part B without qualifying coverage from an employer, you’ll face a late enrollment penalty that increases your monthly premium for as long as you have Part B. The penalty grows the longer you wait, so even a year or two of delay can add a noticeable surcharge to every premium payment going forward. You may also have to wait for the next General Enrollment Period (January through March each year), leaving you without coverage in the gap.
What Parts A and B Don’t Cover
Original Medicare has some significant gaps. The following are not covered:
- Dental care: routine cleanings, fillings, extractions, and dentures
- Vision: eye exams for prescription glasses and the glasses themselves
- Hearing: hearing aids and the exams to fit them
- Long-term care: custodial care in a nursing home when you don’t need skilled medical services
- Most prescription drugs: Part B covers only a narrow set of outpatient medications; routine prescriptions require a separate Part D plan
- Cosmetic surgery
- Massage therapy
- Routine physical exams (though the annual wellness visit is covered)
- Concierge or boutique medicine fees
The dental, vision, and hearing exclusions are the ones that affect the most people. Many Medicare Advantage plans (Part C) bundle these benefits in, which is a primary reason some enrollees choose Advantage over Original Medicare. For prescription drug coverage, you’ll need to enroll in a standalone Part D plan or select a Medicare Advantage plan that includes drug coverage.
How Part A and Part B Work Together
In practice, the two parts often overlap during a single medical event. If you break a hip, Part A covers your hospital stay and surgery. Once you’re discharged, Part B covers your follow-up doctor visits and outpatient physical therapy. If you then need skilled nursing care, Part A steps back in for up to 100 days, provided you had that qualifying 3-day inpatient stay. Your durable medical equipment, like a walker, falls under Part B.
The key distinction is the setting. Inpatient care runs through Part A. Outpatient and physician services run through Part B. Some services, like home health care, can be covered by either part depending on the circumstances. When you receive a bill, the “Part” determines which deductible and coinsurance rules apply, so knowing the difference helps you anticipate your costs before a procedure rather than after.