Medicare Part A vs. Part B: What’s the Difference?

Quick answer: Medicare Part A covers hospital, skilled nursing, and hospice care. Part B covers doctor visits, outpatient care, and medical supplies. Most people get Part A for free and pay a monthly premium for Part B — and most people need both.

If you’re new to Medicare, “Part A” and “Part B” can sound like two halves of the same thing — but they actually cover very different types of care, and understanding the split matters when you’re deciding how (and when) to enroll.

Medicare Part A: Hospital Insurance

Part A is often called “hospital insurance” because that’s its core job — but it covers more than just hospital stays. It helps pay for:

• Inpatient hospital care
• Skilled nursing facility care (after a qualifying hospital stay)
• Hospice care
• Some home health care

Here’s the part that surprises a lot of people: about 99% of beneficiaries pay $0/month for Part A, because it’s funded by the Medicare payroll taxes you (or your spouse) paid throughout your working years. If you or your spouse worked at least 10 years (40 quarters) in Medicare-covered employment, your Part A premium is free.

Free premium doesn’t mean free care, though — Part A still has a deductible and coinsurance if you’re actually hospitalized, which is one of the main reasons people look into a Medicare Supplement plan.

Medicare Part B: Medical Insurance

Part B is your everyday medical coverage — the care you receive outside of a hospital stay. It covers:

• Doctor visits and specialist appointments
• Outpatient care and procedures
• Preventive services (screenings, vaccines, annual wellness visits)
• Durable medical equipment, like wheelchairs and walkers

Unlike Part A, Part B is not free for most people — there’s a standard monthly premium (which can be higher for higher-income beneficiaries through IRMAA), plus an annual deductible and 20% coinsurance on most services after that deductible is met.

Do You Need Both?

For the vast majority of people, yes. Part A and Part B together make up “Original Medicare,” and they’re designed to complement each other — Part A handles the big inpatient events, Part B handles the ongoing, everyday care. Having only one or the other leaves a real gap: Part A alone won’t cover your doctor visits, and Part B alone won’t cover a hospital stay.

When Do You Enroll?

If you’re already receiving Social Security benefits, you’re typically enrolled in both Part A and Part B automatically starting the month you turn 65. If you’re not yet collecting Social Security, you’ll need to actively sign up during your 7-month Initial Enrollment Period surrounding your 65th birthday — it starts 3 months before your birthday month and ends 3 months after.

Missing that window matters. If you don’t sign up for Part B when you’re first eligible and don’t qualify for a Special Enrollment Period (for example, because you’re still covered by an employer group plan), you could face a late enrollment penalty that permanently increases your Part B premium — and you may have to wait for the next General Enrollment Period to sign up at all.

Can You Delay Part B?

Yes, in certain situations — most commonly if you’re still working past 65 and covered by a current employer’s group health plan (with 20 or more employees). In that case, you can often delay Part B without penalty until that employer coverage ends, then enroll during a Special Enrollment Period. This is a genuinely common situation, and getting the timing right matters, since enrolling too early or too late can both create problems.

Part A is a little different — since it’s premium-free for most people, there’s rarely a reason to delay it, even if you’re still working. One exception: if you’re contributing to a Health Savings Account (HSA), enrolling in Part A can affect your ability to keep contributing, since HSA rules require you not be enrolled in any part of Medicare.

What About the Gaps?

Even with both Part A and Part B working together, Original Medicare was never designed to cover 100% of your costs. You’re still responsible for deductibles, coinsurance, and — critically — there’s no annual limit on how much you could pay out of pocket in a bad year. That’s exactly the gap a Medicare Supplement (Medigap) plan exists to fill, and it’s worth understanding before you’re facing a hospital bill, not after.