Medicare Advantage is not automatically an HMO, but HMOs are the most common type of Medicare Advantage plan. Medicare Advantage (also called Part C) is a broader category of private insurance plans that includes HMOs, PPOs, Private Fee-for-Service plans, Special Needs Plans, and Medical Savings Account plans. When people equate Medicare Advantage with an HMO, it’s usually because so many enrollees end up in one.
How Medicare Advantage Plans Are Structured
Medicare Advantage is the private-sector alternative to Original Medicare. Instead of getting Parts A and B directly from the federal government, you enroll in a plan run by a private insurance company that contracts with Medicare. That plan must cover everything Original Medicare covers, but it can also add extras like dental, vision, hearing, and prescription drug coverage.
Within Medicare Advantage, you choose a specific plan type. Medicare.gov lists five:
- HMO (Health Maintenance Organization)
- PPO (Preferred Provider Organization)
- PFFS (Private Fee-for-Service)
- SNP (Special Needs Plan)
- MSA (Medical Savings Account)
Each type has different rules about which doctors you can see, whether you need referrals, and how much you’ll pay out of pocket. The plan type you pick shapes your day-to-day experience with Medicare more than almost any other decision.
What Makes an HMO Plan Different
If you enroll in a Medicare Advantage HMO, three rules define how your coverage works. First, you typically need to choose a primary care doctor within the plan’s network. Second, you generally need a referral from that doctor before seeing a specialist. Third, the plan only covers care from in-network providers, except in emergencies or when you need urgent care while traveling.
That last point is the biggest practical difference. If you see an out-of-network doctor for routine care, an HMO will not pay for it. You’re responsible for the entire bill. This makes HMOs less flexible than some other plan types, but the tradeoff is cost: HMO premiums tend to be lower, and many plans charge $0 on top of your Part B premium.
HMO vs. PPO: The Most Common Choice
Most people choosing a Medicare Advantage plan are deciding between an HMO and a PPO. The core difference is network flexibility. A PPO lets you see any provider, including out-of-network doctors, though you’ll pay more for going outside the network. You also don’t need referrals to see specialists. That freedom comes at a price: PPOs generally charge higher monthly premiums than HMOs.
With an HMO, you’re limited to doctors in your plan’s service area. You can’t see an out-of-network specialist on your own and expect coverage. But your copays for in-network visits are often lower, and the simpler structure means fewer surprise costs. If your preferred doctors are already in an HMO’s network and you don’t mind getting referrals, the savings can be significant over the course of a year.
The Less Common Plan Types
Private Fee-for-Service plans work differently from both HMOs and PPOs. You can go to any Medicare-approved provider who accepts the plan’s payment terms, with no referrals and no requirement to pick a primary care doctor. The catch is that providers can decide visit by visit whether to accept the plan, so your access isn’t as predictable.
Special Needs Plans are designed for people with specific chronic conditions, those who qualify for both Medicare and Medicaid, or those living in certain institutional settings. A SNP can be structured as either an HMO or a PPO, so the referral and network rules depend on which version you join. All SNPs must include prescription drug coverage.
Medical Savings Account plans pair a high-deductible insurance plan with a savings account that Medicare deposits money into each year. You use that account to pay for care until you hit your deductible. These plans have no network restrictions, no referral requirements, and no separate monthly premium beyond Part B. They don’t cover prescription drugs, so you’d need a standalone Part D plan.
What All Medicare Advantage Plans Share
Regardless of type, every Medicare Advantage plan must cover all medically necessary services that Original Medicare covers. Plans can add benefits, but they can’t take away core coverage. Every plan also sets a yearly maximum on your out-of-pocket spending for covered services. Once you hit that cap, the plan pays 100% for the rest of the year. Original Medicare has no equivalent cap, which is one reason people choose Medicare Advantage in the first place.
There are tradeoffs that apply across all plan types, though. You may need prior authorization before the plan covers certain services or procedures. You generally can’t buy a Medigap (Medicare Supplement) policy to fill coverage gaps. And most plans don’t cover medical care outside the United States, though some offer limited emergency coverage abroad.
How to Tell What Type of Plan You Have
If you’re already enrolled in Medicare Advantage and aren’t sure whether your plan is an HMO, check your plan’s “Evidence of Coverage” document or log into your Medicare.gov account. The plan type is listed on your membership card in most cases. If your card says “HMO,” you’re in an HMO. If it says “PPO” or “HMO-POS” (a hybrid that allows some out-of-network care), that’s a different structure with different rules.
As of 2025, about 34.1 million Medicare beneficiaries are enrolled in Medicare Advantage plans, representing 54% of all eligible Medicare recipients. With that many people in private plans, and HMOs being the most widely offered option in many markets, it’s easy to see why the two terms get used interchangeably. But knowing the distinction helps you pick the plan that actually fits how you use healthcare.