Medicare is divided into Parts A, B, C and D: they cover different aspects of health care, and your costs and enrollment steps depend on the coverage you choose. Understanding how the Parts fit together can help you compare options and know when to enroll.
This guide explains Medicare Parts, costs and enrollment, including how Original Medicare differs from Medicare Advantage. For a broader look at UnitedHealthcare plans, coverage, networks and care, see our guide, “UnitedHealthcare: A Guide to Plans, Coverage, Networks, and Care.”
| Option | What it provides | Key consideration |
|---|---|---|
| Part A | Hospital insurance | May have a premium depending on work history |
| Part B | Medical insurance | Monthly premium and cost-sharing apply |
| Part C | Medicare Advantage through private plans | Check provider networks and plan costs |
| Part D | Prescription drug coverage | Compare plan formularies and costs |
- 4 parts: A, B, C and D The named parts of Medicare
- 7 months Length of the Initial Enrollment Period around age 65
- 65 years The age at which Medicare eligibility commonly begins
What does each Medicare part cover?
Medicare Parts A and B form Original Medicare: Part A covers eligible inpatient hospital care and certain skilled nursing facility care, while Part B covers medically necessary medical services, including doctor visits and outpatient care, plus some preventive services.
Parts A and B
- Part A: Hospital insurance for eligible inpatient care and certain skilled nursing facility care. It does not cover long-term custodial care, such as ongoing help with daily activities when that is the only care needed.
- Part B: Medical insurance for medically necessary services such as doctor visits and outpatient care, as well as some preventive services.
- Original Medicare: The combined name for Part A and Part B coverage.
Parts C and D
- Part C, or Medicare Advantage: An alternative way to receive Part A and Part B benefits.
- Part D: Prescription drug coverage provided through private plans.
Part C and Original Medicare are different ways to receive Part A and Part B benefits; Part D addresses prescription drugs through private plans. These are distinct coverage categories, so check which parts a plan includes when comparing Medicare options.
Who qualifies for Medicare, and when can they enroll?
Age and other eligibility routes
Medicare eligibility commonly begins at age 65, but some people qualify earlier through disability, End-Stage Renal Disease (ESRD) or amyotrophic lateral sclerosis (ALS). These routes differ, so eligibility before 65 depends on the person’s specific circumstances.
- Age: the common starting threshold is 65.
- Earlier eligibility: disability, ESRD or ALS may provide another route.
The seven-month initial window
The Initial Enrollment Period lasts seven months: it covers the three months before the month you turn 65, your birthday month and the three months after. For example, if your 65th birthday is in July, the window runs from April through October.
Qualifying health coverage through current employment may let you delay Part B without a late-enrollment penalty, but the rules depend on the coverage and your circumstances. Check Medicare.gov, the official place to review eligibility and current enrollment rules; do not assume Social Security and Medicare enrollment follow the same timing for everyone.
What do Medicare premiums and out-of-pocket costs include?
Premiums
Medicare costs can include monthly premiums, deductibles and cost-sharing, and having Medicare does not make every covered service free. Part A may have no monthly premium for people who meet its work-history requirements; people who do not meet them may have to pay one.
Part B has a monthly premium, and its standard amount can change each calendar year. Income can also affect the Part B amount, so check the current premium information rather than assuming last year’s figure still applies.
Deductibles and plan costs
Part A and Part B can involve deductibles and cost-sharing, meaning you may pay some costs yourself when you receive covered care. Part D and Medicare Advantage costs depend on the plan, location and coverage you choose; compare current plan documents before enrolling, not an old price.
- Part A: Check whether your work history qualifies you for a premium-free Part A, and review its deductible and cost-sharing.
- Part B: Check the current calendar-year premium and whether income changes the amount, as well as applicable deductibles and cost-sharing.
- Part D and Medicare Advantage: Compare current plan documents for the plans available in your location, including their premiums and other cost-sharing.
How does Medicare Advantage differ from Original Medicare?
Provider access
Original Medicare uses Part A and Part B, while Medicare Advantage (Part C) is a private-insurance alternative that combines Part A and Part B coverage. With Original Medicare, beneficiaries can generally see providers who accept Medicare; Medicare Advantage plans may limit access through provider networks and set their own cost-sharing.
- Original Medicare: Check that a doctor or hospital accepts Medicare.
- Medicare Advantage: Check whether preferred doctors and hospitals are in the plan’s network, and review its cost-sharing rules.
Prescription and supplemental coverage
Original Medicare does not include Part D automatically, so beneficiaries can choose a separate Part D plan for prescription coverage. Many Medicare Advantage plans include Part D, but coverage varies by plan; check that the medicines you use are covered.
- Original Medicare: Part A and Part B, with a separate Part D plan available for prescriptions.
- Medicare Advantage: Part A and Part B through a private insurer; many plans also include Part D.
Original Medicare and Medicare Advantage are different coverage routes, not options to use together. A person generally cannot use Medicare Advantage alongside a separate Medigap policy, so compare provider access, prescription coverage and plan-specific costs before choosing.
When does Medicare not cover a service, or create a coverage gap?
Coverage limits
Original Medicare can leave gaps for long-term custodial care and outpatient prescriptions, while Medigap may help with certain out-of-pocket costs but cannot be used with Medicare Advantage. These limits matter when comparing coverage options:
- Custodial care: Original Medicare generally does not cover most long-term care that helps with everyday activities, such as bathing or dressing.
- Prescription drugs: Original Medicare does not include most outpatient prescription drug coverage; a separate Part D plan may be needed.
- Out-of-pocket costs: Medigap can help pay certain costs under Original Medicare, but it does not work with Medicare Advantage.
Avoiding enrollment assumptions
Delaying Part B can create an enrollment problem if existing coverage does not qualify for a Special Enrollment Period. Do not assume that having another health plan automatically gives you an exception: eligibility depends on the specific coverage and circumstances.
Before postponing Part B, ask Social Security or Medicare whether your existing coverage qualifies for a Special Enrollment Period. Confirm the answer for your situation before relying on an exception, rather than discovering later that the delay affected your enrollment options.
How does Medicare fit with employer coverage or other insurance?
Coordination of coverage
Medicare can coordinate with employer-sponsored insurance, but which plan pays first depends on factors such as whether the coverage comes from current employment and the type of plan. Before delaying Medicare Part B, confirm that the employer plan is based on current employment and ask the plan administrator whether you can enroll in Part B later without a penalty. Do not assume that every employer plan qualifies for the same enrollment rules.
Comparing options
Compare the employer plan with Medicare’s separate coverage choices before deciding which to keep. Check the specific plan documents and provider directory, and compare:
- Employer-sponsored insurance: its premiums, whether your providers are in network, and the prescription benefits it includes.
- Medicare Part B: its premium and coverage alongside the employer plan, including which insurer pays first.
- Medicare Part D: its prescription coverage against the medicines and pharmacy access available through the employer plan.
For a broader look at insurance plans, coverage and networks, read “UnitedHealthcare: A Guide to Plans, Coverage, Networks, and Care.”
Frequently asked questions
Is Medicare the same as Medicaid?
Can I get Medicare before age 65?
Can I delay Part B if I have insurance through work?
Does Medicare cover prescription drugs?
Key takeaways
- Original Medicare consists of Part A and Part B; Part D adds outpatient prescription coverage.
- The Initial Enrollment Period lasts seven months around a person’s 65th birthday.
- Medicare Advantage is Part C and may use plan-specific provider networks and cost-sharing.
- Most long-term custodial care is not covered by Original Medicare.
- Confirm employer coverage rules before delaying Part B.
