The Parts of Medicare, Explained: A, B, C and D

The four parts, and what Original Medicare means

Medicare basics start here: it is the federal health insurance program for people 65 and over, and for some younger people with a disability, permanent kidney failure or ALS. It is run by the Centers for Medicare and Medicaid Services. Medicare eligibility usually begins at 65, and your initial enrollment period is the seven months around that birthday, which is when you can first sign up. Parts A and B together are what people mean by Original Medicare, and they come from the government. Parts C and D come from private insurers approved by Medicare.

• Part A: Hospital insurance.
• Part B: Medical insurance.
• Part C: Medicare Advantage, a private alternative that delivers your A and B benefits.
• Part D: Prescription drug coverage.

Part A: hospital insurance

Part A covers inpatient care, and most people pay no premium for it because they or a spouse paid Medicare taxes for about 10 years. Free of premium is not free of cost, though. You pay $1,736 per benefit period, and a benefit period is not a calendar year: it ends after 60 days out of hospital, so it is possible to pay it more than once in a year. Long stays add daily coinsurance on top.

• What it covers: Inpatient hospital stays, skilled nursing after a qualifying hospital stay, hospice, and some home health care.
• Days 61 to 90: $434 a day.
• Lifetime reserve days: $868 a day, 60 of them in your whole life, and they never renew.
• Skilled nursing, days 21 to 100: $217 a day. The first 20 days cost nothing.

Part B: medical insurance

Part B covers medically necessary outpatient care and preventive services: doctor visits, same-day surgery, emergency care, lab tests and imaging, durable equipment like walkers and oxygen, home health services, and screenings and the annual wellness visit. Almost everyone pays a monthly premium, $202.90 as the 2026 standard amount, with higher earners paying more through IRMAA. After the $283 annual deductible you generally pay 20% of the approved amount. Skip Part B when first eligible without other qualifying coverage and a late enrollment penalty applies for as long as you hold it, though a Special Enrollment Period protects you if you or your spouse are still working with employer coverage.

Part C: Medicare Advantage

Medicare Part C, also called Medicare Advantage, is a way of receiving your Part A and Part B benefits through a private plan rather than directly from the government, and most plans add extra benefits on top. Such a plan must cover everything Original Medicare covers, with one exception: hospice stays with Original Medicare and is paid for outside the plan. You keep paying your Part B premium, plus whatever the plan charges on top, which is often nothing.

• Usually includes drugs: Most plans bundle Part D coverage in.
• Networks: Typically HMO or PPO, and some care needs a referral or prior approval.
• Set copays: A fixed amount per visit rather than 20% coinsurance.
• An annual cap: Every plan must limit your yearly out-of-pocket costs for covered medical care. Original Medicare has no such limit.
• Extras: Routine dental, vision and hearing are commonly included.

Part D: prescription drug coverage

Medicare Part D comes either as a stand-alone plan added to Original Medicare or built into a Medicare Advantage plan. Every plan has a formulary, its own list of covered drugs, which is why two plans can differ enormously for the same person. Federal limits apply whichever you choose: no plan's deductible can exceed $615 in 2026, once your out-of-pocket drug costs reach $2,100 you pay nothing more for covered drugs that year, and covered insulin is capped at $35 for a month's supply. Go 63 days or more without creditable drug coverage and a penalty is added to your premium.

Medigap, which is not a part of Medicare

A Medicare Supplement plan, usually called Medigap, is sold by private insurers to cover the gaps Original Medicare leaves, such as deductibles and coinsurance. It is not a part of Medicare and it works only alongside Original Medicare. You cannot hold it with a Medicare Advantage plan. Plans are standardized by letter, so Plan G from one insurer has identical benefits to Plan G from another and price is the main difference. Plan G covers every Medigap benefit except the Part B deductible, and its high-deductible version requires you to pay $3,050 first in 2027. Plan N often costs less in premium but leaves small charges on some office and emergency visits. None of them include drug coverage, so most people pair one with a Part D plan.

What Original Medicare does not cover

Knowing the holes is what makes the next decision make sense, because every one of these is a reason people add coverage.

• Most prescription drugs: You need Part D, or a plan that includes it.
• Routine dental and dentures: Not covered.
• Routine eye exams and glasses: Not covered.
• Hearing aids: Not covered.
• Long-term custodial care: Not covered, which surprises people the most.
• Care outside the U.S.: Not covered in most circumstances.
• Any annual limit on your costs: There is no out-of-pocket maximum at all in Original Medicare.

The choice that shapes everything else

You combine the parts in one of exactly two ways, and you cannot mix them. These are your Medicare coverage options in practice, and this is the decision people get wrong, usually by comparing premiums alone. Comparing the paths properly means looking at your doctors and prescriptions, not the monthly figure.

• Path 1: Original Medicare plus Medigap plus Part D: Any provider in the U.S. who accepts Medicare, no networks and no referrals. You pay more in monthly premiums and usually very little when you receive care.
• Path 2: Medicare Advantage: One plan covering hospital and medical care, usually drugs, often with extras. Lower premiums, but copays as you go, a network to stay inside, and no Medigap allowed.
• How to actually choose: Travel often or want any doctor, and Path 1 tends to fit. Want lower monthly costs and extras bundled in, and Path 2 does. Your prescriptions and your doctors decide it more reliably than the premium does.

Common questions

More in Medicare 101

• Turning 65: Your complete guide to starting Medicare
• Medicare Eligibility: Who Qualifies, and When
• How to Enroll in Medicare, Step by Step
• Medicare and Working Past 65: When to Enroll and What to Keep
• Medicare Enrollment Periods: Every Window Explained
• Medicare Late Enrollment Penalties, and How to Avoid Them
• Medicare Costs: What You'll Actually Pay
• Medicare Advantage vs. Medicare Supplement: How to Choose
• Medicare Prescription Drug Coverage: Where It Comes From and How It Works