Medicare covers more than 65 million Americans — and yet for the people who need it most, it remains persistently confusing. The rules around what's covered, what isn't, what requires prior authorization, and what to do when something is denied are genuinely complex. And the stakes are high: misunderstanding your coverage can mean unexpected costs, delayed care, or missed benefits you didn't know you had.
This guide is intended as a clear, accessible starting point — not a comprehensive policy reference, but a foundation for navigating Medicare with more confidence.
The four parts of Medicare, explained simply
Medicare is divided into four parts, each covering different types of care.
Part A covers hospital care — inpatient hospital stays, skilled nursing facility care following a qualifying hospital stay, hospice, and some home health services. Most people don't pay a monthly premium for Part A if they or their spouse worked and paid Medicare taxes for at least 10 years.
Part B covers outpatient care — doctor's visits, preventive services, lab tests, imaging, durable medical equipment, and many specialist services. Part B has a monthly premium, an annual deductible, and typically requires a 20% coinsurance payment after the deductible is met. There is no out-of-pocket maximum under Original Medicare.
Part C, also called Medicare Advantage, is an alternative way to receive Medicare benefits through a private insurance company. These plans are required to cover everything Original Medicare covers, but many have additional benefits — and many have prior authorization requirements that Original Medicare does not.
Part D covers prescription drugs. It's offered through private insurers and is available as a standalone plan (if you have Original Medicare) or bundled into a Medicare Advantage plan.
Medicare Advantage vs. Original Medicare: a critical distinction
One of the most important things to understand is that Medicare Advantage (Part C) operates differently from Original Medicare (Parts A and B) in ways that significantly affect how you access care.
With Original Medicare, you can generally see any doctor or specialist who accepts Medicare — which is the vast majority of providers nationwide. With Medicare Advantage, you are typically required to use a network of providers and may need referrals to see specialists.
Medicare Advantage plans also frequently require prior authorization for procedures, hospitalizations, specialist visits, and medical equipment. This is not a feature of Original Medicare. Understanding which type of Medicare you have — and what its rules are — is essential before scheduling any significant care.
Common coverage gaps and what they mean
Medicare, particularly Original Medicare, has several well-known coverage gaps:
- No out-of-pocket maximum under Original Medicare means that in theory, costs can be unlimited. Most people address this by purchasing a Medigap (supplemental) policy.
- Skilled nursing facility care is covered only after a qualifying 3-day inpatient hospital stay — and only for a limited time. Custodial long-term care is not covered.
- Dental, vision, and hearing are not covered under Original Medicare, though some Medicare Advantage plans include these benefits.
- Prescription drugs are not covered under Original Medicare (Parts A and B) — you need a separate Part D plan or a Medicare Advantage plan that includes drug coverage.
Prior authorization under Medicare Advantage
If you have Medicare Advantage, prior authorization is one of the most important concepts to understand. It means that before you receive certain services — including some surgeries, imaging studies, specialist visits, and durable medical equipment — your insurance plan must approve them in advance.
Prior authorization denials are common and are frequently overturned on appeal. If you or your doctor's office is told that authorization has been denied, this is not necessarily the final answer. The appeals process exists specifically for this purpose, and patients have the right to request an expedited review when delay would harm their health.
Your right to appeal
Both Original Medicare and Medicare Advantage plans have formal appeals processes when coverage is denied. You have the right to appeal any decision, and there are multiple levels of appeal available.
For Medicare Advantage, the process begins with a plan-level appeal. If that's denied, you can escalate to an Independent Review Entity, and from there through several additional levels up to federal court if necessary.
Denials are not final decisions. Many are overturned, especially when accompanied by clear documentation from the treating physician explaining why the service is medically necessary.
Where to get unbiased help
One of the challenges with Medicare is that much of the "help" available comes from insurance brokers who are paid to sell plans. Their guidance may be accurate, but their incentives don't always align perfectly with yours.
For unbiased, free Medicare counseling, the State Health Insurance Assistance Program (SHIP) offers one-on-one assistance in every state. SHIP counselors are trained volunteers with no financial stake in the plans they discuss.
If your Medicare-related needs go beyond basic counseling — if you're dealing with a denial, a billing dispute, or a complex coverage question — a healthcare advocate with Medicare experience can provide more personalized, situation-specific support.
Understanding your Medicare coverage doesn't require becoming an expert. It requires knowing the right questions to ask — and knowing where to turn when the answers aren't clear.