Medicare Parts A, B, C, and D Explained — Simply
Medicare has four parts — A, B, C, and D — and the differences between them are not obvious from the names. Part A covers hospitals. Part B covers doctors. Part C is an alternative way to get A and B through a private plan. Part D covers prescription drugs. Getting the structure wrong when you enroll can leave you with unexpected costs or coverage gaps. Here is a plain-language breakdown of each part, what it costs, and the enrollment rules that catch people off guard.
Written by the Uplift editorial team · Reviewed against official federal program sources
Part A: hospital insurance
Medicare Part A covers inpatient hospital stays, skilled nursing facility care after a qualifying hospital stay, hospice care, and some home health care. For most people, Part A is premium-free — if you or your spouse worked and paid Medicare taxes for at least 10 years (40 quarters), you owe no monthly premium for Part A.
Part A does have a deductible and cost-sharing. In 2024, the inpatient deductible is $1,632 per benefit period (not per year — a distinction that matters for multiple hospitalizations). For stays longer than 60 days, daily coinsurance applies. Skilled nursing facility stays beyond 20 days also involve daily cost-sharing.
Part A alone does not cover outpatient care, doctor visits, preventive services, durable medical equipment, or prescription drugs. Enrolling in Part A without Part B leaves major gaps.
Part B: medical insurance
Medicare Part B covers outpatient medical services — doctor visits, specialist care, preventive services (including many vaccines and cancer screenings at no cost), outpatient mental health, physical therapy, and durable medical equipment. Part B is not premium-free.
The standard Part B premium in 2024 is $174.70 per month, deducted automatically from Social Security if you receive it. Higher-income enrollees pay more under the Income-Related Monthly Adjustment Amount (IRMAA) surcharge, which applies to individuals with income above $103,000 and couples above $206,000.
Part B has a $240 annual deductible in 2024, after which you generally pay 20% of Medicare-approved costs with no out-of-pocket maximum. This 20% coinsurance without a cap is a significant financial exposure for major illnesses — one reason most Medicare beneficiaries obtain supplemental coverage through Medigap or a Medicare Advantage plan.
Part C: Medicare Advantage
Medicare Advantage (Part C) is an alternative way to receive your Medicare benefits through a private insurance company that contracts with Medicare. Instead of getting your Part A and B benefits directly from Medicare, you get them through an Advantage plan that must cover at least the same benefits as traditional Medicare.
Most Medicare Advantage plans also include Part D drug coverage and additional benefits not covered by traditional Medicare — dental, vision, hearing, fitness memberships, and transportation to medical appointments. These extra benefits are a major reason enrollment in Medicare Advantage has grown rapidly, now covering more than half of all Medicare beneficiaries.
The trade-off is that Medicare Advantage plans typically operate as HMOs or PPOs with provider networks. You may not be able to see any Medicare-accepting provider the way you could under traditional Medicare — you are generally limited to in-network providers. For people with established relationships with specific specialists, checking network coverage before switching to an Advantage plan is essential.
Part D: prescription drug coverage
Medicare Part D covers prescription drugs through private insurance plans. If you have traditional Medicare (Parts A and B), you add Part D separately by enrolling in a standalone Prescription Drug Plan (PDP). If you have Medicare Advantage, drug coverage is usually included.
Part D plans vary significantly in which drugs they cover, what tier a specific drug falls on, and what cost-sharing you owe. The Medicare Plan Finder at medicare.gov/plan-compare allows you to enter your specific medications and compare the total annual cost across available Part D plans in your area.
Missing your Part D enrollment window — which opens three months before you turn 65 and closes three months after — triggers a late enrollment penalty: a permanent premium increase of 1% per month for every month you went without creditable drug coverage. If you have drug coverage through an employer that qualifies as "creditable," you can delay Part D without penalty.
Enrollment timing and the gaps that cost people
The Initial Enrollment Period for Medicare runs from three months before your 65th birthday through three months after — a seven-month window. Enrolling in Part B late triggers a permanent 10% premium penalty per year of delayed enrollment (with an exception if you had qualifying employer coverage).
If you are still working at 65 and have employer health coverage, you may be able to delay Medicare enrollment without penalty — but the rules are specific and depend on whether your employer has 20 or more employees. Getting this wrong can result in penalties or coverage gaps when you eventually do enroll.
The Extra Help program (Low Income Subsidy) provides significant assistance with Part D premiums and cost-sharing for Medicare beneficiaries with income below 150% FPL. An estimated 2 million eligible people do not receive it. If your income is near or below this threshold, check eligibility at ssa.gov/extrahelp.