Medicare Parts A, B, C, and D Explained

Medicare.gov describes the parts this way.

• Part A, hospital insurance. Inpatient hospital care, skilled nursing facility care, hospice care, and home health care.
• Part B, medical insurance. Doctors and other providers, outpatient care, home health care, durable medical equipment such as wheelchairs and walkers, and many preventive services.
• Part D, drug coverage. Prescription drugs, including many recommended shots and vaccines. It is run by private insurers under Medicare rules.
• Part C, Medicare Advantage. A private plan approved by Medicare that bundles Part A, Part B, and usually Part D.

Medigap sits outside that list. Medicare.gov calls it extra insurance bought from a private company to help pay a person's share of costs in Original Medicare. Policies are standardized and, in most states, named by letters such as Plan G or Plan K. The benefits in each lettered plan are identical no matter who sells it.

Medicare.gov splits cancer treatment across two parts based on where it is given.

Part A covers chemotherapy for a hospital inpatient. Part B covers chemotherapy given to a hospital outpatient, in a doctor's office, or in a freestanding clinic.

The cost rule follows. After the Part B deductible, the usual share is 20% of the Medicare-approved amount for chemotherapy in a doctor's office, freestanding clinic, or hospital outpatient setting. In a hospital outpatient setting, Medicare.gov says the copayment will not exceed the inpatient hospital deductible amount.

Clinical trials get their own line. Medicare.gov says Part A and Part B cover some costs of certain clinical research studies, such as office visits and tests, with the usual 20% share after the Part B deductible.

Medicare.gov publishes these figures for 2026.

Most people pay no Part A premium, because they or a spouse paid Medicare taxes for generally at least 10 years. For those who do not qualify, the premium is either $311 or $565 a month.

The Part A deductible is $1,736 for each inpatient hospital benefit period. Medicare.gov is explicit that there is no limit on the number of benefit periods in a year, so that deductible can be owed more than once in twelve months.

Inpatient days are priced in tiers. Days 1 through 60 cost $0 after the deductible. Days 61 through 90 cost $434 each. Days 91 through 150 cost $868 each, drawing on 60 lifetime reserve days. After day 150, the patient pays all costs.

Skilled nursing works the same way. Days 1 through 20 cost $0. Days 21 through 100 cost $217 each. From day 101, the patient pays all costs.

Hospice care is $0 for covered services, with a copayment of up to $5 for each prescription drug for pain relief and symptom control at home, and 5% of the approved amount for inpatient respite care.

The standard Part B premium is $202.90 a month in 2026, higher for higher incomes. It is owed every month, whether or not any services are used.

The Part B deductible is $283, paid once each year. After that, the usual share is 20% of the cost for each covered service, provided the doctor accepts the Medicare-approved amount as full payment, which Medicare.gov calls accepting assignment.

Two lines are worth knowing during cancer care. Covered clinical laboratory services cost $0. And in a hospital outpatient clinic, there is an added copayment to the hospital, which in most cases will not be more than the Part A hospital deductible. Medicare.gov notes plainly that the same service can cost more in a hospital outpatient department than in a doctor's office.

Part D now has three stages, and the third one is new enough that many summaries have not caught up.

In 2026, no Medicare drug plan may have a deductible above $615, and some have none. After the deductible, the initial coverage stage charges 25% coinsurance for generic and brand-name drugs. That continues until out-of-pocket spending on covered Part D drugs reaches $2,100 in 2026, including certain payments made on a person's behalf through the Extra Help program.

Then catastrophic coverage starts automatically. Medicare.gov states that after that point there is no out-of-pocket cost for covered Part D drugs for the rest of the calendar year.

For anyone taking an expensive oral cancer drug, that $2,100 figure is the number that defines the worst case for the year, as long as the drug is on the plan's list.

Medicare.gov states it directly: there is no yearly limit on out-of-pocket costs unless a person has supplemental coverage such as Medigap, or joins a Medicare Advantage plan.

That is the structural difference between the two paths. Original Medicare can be used with any doctor or hospital that takes Medicare, anywhere in the United States, including all 50 states, the District of Columbia, Puerto Rico, the US Virgin Islands, Guam, the Northern Mariana Islands, and American Samoa. Medicare Advantage plans usually require network doctors and prior approval for certain drugs or services, but they carry an out-of-pocket limit, after which the plan pays 100% of covered services for the rest of the calendar year.

Medicare Advantage enrollees still pay the Part B premium. Medicare.gov is explicit that a person must have Part B and keep paying that premium to stay in the plan. The same rule applies to keeping a Medigap policy.

The Initial Enrollment Period lasts 7 months. It starts 3 months before the month someone turns 65 and ends 3 months after that month.

Missing it has consequences. Medicare.gov says a late enrollment penalty for Part B is paid monthly for as long as Part B is held, and grows the longer someone waits. The General Enrollment Period runs January 1 through March 31 each year, with coverage starting the month after signup.

Part D has its own trap. The penalty applies to anyone who goes 63 days or more without creditable drug coverage, meaning coverage similar in value to Part D. Medicare.gov suggests joining a low-premium drug plan even for people taking few drugs, precisely to avoid it.

People with limited income and resources may qualify for state help with premiums and other costs, and for Extra Help with drug costs. Medicare.gov says qualifying for Extra Help also removes the Part D late enrollment penalty.

Cancer-specific coverage questions are handled in Medicare and cancer. The difference between the two programs is drawn in Medicare vs. Medicaid. Having both at once is covered in dual eligibility.

• Medicare.gov: parts of Medicare
• Medicare.gov: costs
• Medicare.gov: drug coverage costs
• Medicare.gov: chemotherapy coverage
• Medicare.gov: clinical research studies
• Medicare.gov: when coverage starts