What Is Medicare Part A and B? A Clear Breakdown

Medicare can feel like a maze of letters, deadlines, and coverage rules. For millions of Americans approaching age 65, the first question is often: what is Medicare Part A and B? These two parts form what is known as Original Medicare, the foundation of federal health coverage for seniors and certain individuals with disabilities. Understanding them is critical because they determine which hospital and medical services you can access, how much you pay, and whether you need to add extra coverage. This article explains Part A and Part B in plain language, covering costs, enrollment, and what each part actually covers so you can make an informed decision about your healthcare.

Medicare Part A: Hospital Insurance Basics

Medicare Part A is often called hospital insurance because it primarily covers inpatient care in hospitals, skilled nursing facilities, hospice, and some home health services. For most people, Part A comes with a premium of $0 if they or their spouse paid Medicare taxes while working for at least 10 years (40 quarters). This premium-free benefit is one of the biggest advantages of Original Medicare. If you did not pay enough Medicare taxes, you can still buy Part A, but the monthly premium in 2025 is either $278 or $505 depending on your work history.

Part A coverage includes semi-private rooms, meals, nursing care, medications administered during your stay, and lab tests. It also covers a limited stay in a skilled nursing facility after a qualifying hospital stay of at least three days. However, it does not cover long-term custodial care (help with bathing, dressing, or eating) if that is the only care you need. Hospice care for terminal illnesses is fully covered, including pain management and support services.

It is important to note that Part A has deductibles and coinsurance. In 2025, the inpatient hospital deductible is $1,632 per benefit period. A benefit period starts the day you are admitted as an inpatient and ends 60 days after you leave a hospital or skilled nursing facility. If you are readmitted within that 60-day window, you do not pay another deductible. For days 61 through 90 in a hospital, you pay a daily coinsurance of $408. For days 91 through 150 (your lifetime reserve days), the daily coinsurance jumps to $816. After you exhaust your 60 lifetime reserve days, you pay all costs. For a deeper dive into eligibility and costs, see our guide on 2025 Medicare Part A: Is It Free and Who Qualifies?.

Medicare Part B: Medical Insurance Explained

Medicare Part B covers outpatient medical services, including doctor visits, preventive screenings, lab tests, durable medical equipment (like walkers or wheelchairs), ambulance services, and some home health care. Unlike Part A, Part B always requires a monthly premium. In 2025, the standard Part B premium is $185 per month, though higher-income beneficiaries pay more through Income-Related Monthly Adjustment Amounts (IRMAA). The annual Part B deductible is $257 in 2025. After you meet that deductible, you typically pay 20% of the Medicare-approved amount for most services, with no out-of-pocket maximum.

Part B also covers many preventive services at no cost to you, such as annual wellness visits, flu shots, mammograms, and cardiovascular screenings. This emphasis on prevention helps catch health issues early, potentially saving you money and improving outcomes. However, Part B does not cover prescription drugs you take at home (those fall under Part D), most dental care, eye exams for glasses, hearing aids, or long-term care. If you need these services, you must look into separate plans like Medicare Advantage or standalone Part D coverage.

Enrollment in Part B is voluntary, but delaying it can trigger a late enrollment penalty. The penalty is a 10% increase in your Part B premium for each full 12-month period you could have had Part B but did not sign up. This penalty lasts for as long as you have Part B. To avoid this, most people enroll during their Initial Enrollment Period, which begins three months before their 65th birthday and ends three months after. For those still working and covered by employer group health insurance, there is a Special Enrollment Period that allows you to sign up later without penalty. For more on Part B costs, review the latest 2026 IRMAA Brackets for Medicare Part B and Part D: Your Complete Guide.

What Original Medicare (Part A and B) Covers vs. What It Does Not

Original Medicare covers a broad range of medically necessary services, but it leaves significant gaps. Understanding these gaps is key to avoiding surprise bills. Here is a breakdown of what is covered and what is not.

Covered by Part A and B:

• Inpatient hospital stays (semi-private room, meals, nursing, lab tests, medications during stay)
• Skilled nursing facility care (limited, after a qualifying hospital stay)
• Hospice care for terminal illness
• Home health services (part-time skilled nursing, physical therapy, occupational therapy)
• Doctor visits (primary care, specialists, outpatient surgery)
• Preventive services (annual wellness visit, cancer screenings, vaccines)
• Durable medical equipment (wheelchairs, walkers, oxygen equipment)
• Ambulance services (emergency and non-emergency when medically necessary)

Not covered by Part A and B:

• Most prescription drugs (covered by Part D)
• Routine dental care, dentures, and oral surgery
• Routine vision exams, eyeglasses, or contact lenses
• Hearing aids and fitting exams
• Long-term custodial care (assistance with daily living activities)
• Medical care outside the United States (very limited exceptions)
• Cosmetic surgery (unless medically necessary)
• Acupuncture (except for chronic low back pain under certain conditions)

Because of these gaps, many beneficiaries choose to add a Medicare Supplement (Medigap) plan to help cover deductibles, coinsurance, and copays. Others opt for Medicare Advantage (Part C), which bundles Part A, Part B, and often Part D into one plan with an out-of-pocket maximum. Each option has trade-offs, so it is wise to compare plans during the Annual Enrollment Period (October 15 to December 7) or your Initial Enrollment Period.

Enrollment Periods and How to Sign Up

Enrolling in Part A and Part B at the right time can save you from late penalties and coverage delays. There are several enrollment windows to know.

Initial Enrollment Period (IEP): This is your first chance to sign up. It lasts seven months: three months before the month you turn 65, the month of your birthday, and three months after. If you sign up during the first three months, coverage starts the first day of your birthday month. If you wait until the month of your birthday or later, coverage may be delayed by one to three months. Most people who are already receiving Social Security benefits at age 65 are automatically enrolled in Part A and Part B. If you are not receiving benefits, you must actively enroll through the Social Security Administration.

Special Enrollment Period (SEP): If you or your spouse are still working and have group health insurance through an employer, you can delay Part B without penalty. Once that coverage ends (whether you retire or lose the job), you have an eight-month SEP to sign up for Part B. During this period, you can also sign up for Part A if you did not already have it. No late penalty applies if you enroll during the SEP.

General Enrollment Period (GEP): If you miss your IEP and do not qualify for an SEP, you can sign up during the GEP, which runs from January 1 to March 31 each year. However, coverage does not start until July 1, and you may face a late enrollment penalty for Part B (and Part A if you have to buy it). The penalty is permanent for as long as you have Part B. To avoid this, it is almost always better to enroll during your IEP or SEP.

For those with higher incomes, IRMAA surcharges apply to Part B and Part D premiums. These brackets are adjusted annually. To see if you might be affected, read our analysis on 2026 IRMAA Brackets for Medicare Part B Over 65: Are You Affected?.

Costs You Should Expect with Part A and B

Even with premium-free Part A, you still face out-of-pocket costs. Here is a summary of 2025 costs for Original Medicare.

• Part A deductible: $1,632 per benefit period
• Part A daily coinsurance (days 61-90): $408 per day
• Part A lifetime reserve days (days 91-150): $816 per day
• Part B standard monthly premium: $185 (higher for high earners)
• Part B annual deductible: $257
• Part B coinsurance: 20% of Medicare-approved amount for most services

These costs can add up quickly, especially if you have a serious illness or multiple hospital stays. There is no annual out-of-pocket maximum in Original Medicare, which is a major reason many people buy a Medigap policy or switch to Medicare Advantage. Medigap policies cover some or all of these deductibles and coinsurance, giving you predictable costs. Medicare Advantage plans have annual out-of-pocket limits (in 2025, the maximum is $8,300 in-network), but they often require you to use a network of providers. To understand how Part D fits into your overall costs, check out 2025 Medicare Part D Plans: Affordable Coverage You Can Trust.

Frequently Asked Questions

Do I have to enroll in Part B if I have Part A?

Not necessarily, but if you delay Part B and do not have other credible coverage, you will face a late enrollment penalty. Most people enroll in both when they first become eligible to ensure comprehensive coverage.

Can I get Part A for free if I never worked?

If you did not work enough quarters to qualify for premium-free Part A, you may still be able to get it based on your spouse’s work record (if they are at least 62 and you are 65). Otherwise, you can buy Part A by paying a monthly premium.

Does Part A cover emergency room visits?

Part A covers emergency room visits only if you are admitted as an inpatient. If you are treated in the ER and released without admission, Part B covers the ER services (subject to the Part B deductible and 20% coinsurance).

What happens if I keep working past 65?

You can delay Part B if you have group health insurance through your employer (or your spouse’s employer) covering 20 or more employees. Once that coverage ends, you have an eight-month Special Enrollment Period to sign up without penalty.

Is there a penalty for not enrolling in Part A?

If you have to buy Part A (because you do not qualify for premium-free Part A) and delay enrollment, your monthly premium may increase by 10%. You will pay the higher premium for twice the number of years you delayed. For example, if you delayed two years, you pay the penalty for four years.

Making the Right Choice for Your Health and Budget

Understanding what is Medicare Part A and B is the first step toward building a healthcare strategy that protects both your health and your finances. Part A gives you a safety net for hospital stays, while Part B covers your day-to-day medical needs. Together, they form a solid foundation, but they are not complete. Gaps in coverage for drugs, dental, vision, and hearing mean you will likely want to explore additional options like Part D, Medigap, or Medicare Advantage. By learning the rules, costs, and enrollment periods now, you can avoid costly penalties and ensure you have the coverage you need when you need it most. If you have questions about your specific situation, speaking with a licensed insurance agent or contacting the Social Security Administration can help clarify your next steps.