Medicare Advantage HMO Plans 2027 - How They Work

Reviewed by Russell Noga, Licensed Medicare Insurance Broker (all 50 states) — Last updated September 20, 2026

The HMO is the most common kind of Medicare Advantage plan, and the one people most often enroll in without fully understanding what they agreed to. It is not a worse plan than the alternatives. It is a plan built on a specific trade, and whether that trade costs you anything depends entirely on facts about your own life.

This guide covers the rules that define an HMO, what actually happens when you go outside the network, the HMO-POS variant most people have never heard of, and an honest account of who these plans suit.

Some carriers are HMO-only on a given brand. Every plan sold as Keystone 65 in southeastern Pennsylvania is an HMO — the same insurer’s PPO is sold under an entirely different name, which catches people who assume one brand covers both structures.

Every Medicare Advantage HMO for 2027 runs on the same four rules. Everything else about the plan is a variation on these.

• You use the plan’s network. Care from doctors and hospitals inside the network is covered. Care outside it generally is not, with specific exceptions covered below.
• You choose a primary care doctor. Most HMOs ask you to name one. They coordinate your care and are the starting point for most of what follows.
• Specialists usually require a referral. Some plans have relaxed this for certain specialties, but assume you need one unless the plan documents say otherwise.
• You live in the service area. HMOs are sold county by county. Move outside the service area and you generally cannot keep the plan.

The trade is deliberate on the carrier’s part. A defined network and a coordinating physician let the plan predict and control what care costs, and that control is what funds the low premiums and the extra benefits HMOs are known for. You are not getting something for nothing. You are accepting constraints in exchange for price.

This is the single most consequential thing to understand about an HMO, and the place where a misunderstanding costs the most money.

Some HMOs carry the letters POS after the name, for point of service. These plans keep the HMO structure but allow some out-of-network care at a higher cost share, rather than refusing to cover it at all.

If one doctor you are unwilling to give up sits outside an otherwise ideal network, an HMO-POS plan is worth looking for specifically when 2027 plans are released. The flexibility is usually limited, often to particular service categories rather than everything, so read what the plan actually permits rather than assuming it works like a PPO.

These two get conflated constantly and they are not the same thing. A referral is your primary care doctor sending you to a specialist. Prior authorization is the plan approving a service before it is delivered. You can need both, either, or neither, depending on the plan and the service.

Referrals are an administrative step that mostly costs you time. Prior authorization is the one worth investigating before you enroll, because it determines whether the coverage you were sold is coverage you can actually use without a fight. Imaging, planned surgery, skilled nursing stays, infusions and durable medical equipment are the usual candidates.

• Ask the plan directly which of the services you rely on require prior authorization.
• Ask how long a standard decision takes and how long an expedited one takes.
• Check the plan’s customer service and appeals scores, which feed into the Medicare Advantage star ratings and are one of the few public signals on how a plan behaves when you need something approved.

A carrier that controls where you receive care can negotiate harder with the providers in that network, because it is delivering them volume. Those negotiated rates are what allow HMO premiums to sit lower than comparable plans, and what funds the dental, vision, hearing and over-the-counter allowances that HMOs frequently carry.

Benefits vary by plan and by county, and not all plans offer all benefits, so treat any general statement about what HMOs include as a starting point rather than a promise. What is reliably true is the structural relationship: the tighter the network, the more room the plan has on price. Our overview of Medicare Advantage plans for 2027 covers how the plan types compare on cost more broadly.

A low premium is not a low cost

Compare the maximum out-of-pocket, the specialist copay, the hospital cost share and what your prescriptions land at under the plan’s formulary. A zero premium HMO with a high hospital copay can cost more in a bad year than a plan charging a monthly premium.

There is no universally better plan type. There is only whether the constraint an HMO imposes costs you anything in practice.

If your situation is more specific than either list — you have both Medicare and Medicaid, or a chronic condition a plan is built around — a Special Needs Plan may fit better than a standard HMO, and most SNPs are structured as HMOs anyway.

Carriers structure their HMOs differently, and it is worth looking at a specific one to see how the pieces fit together — our breakdown of Aetna Medicare Advantage HMO plans walks through one national carrier’s approach in detail. Regional, health-system-owned carriers take a different route: UPMC for Life HMO plans build the network around the carrier’s own hospitals, which suits people already treated inside that system.

In upstate New York, CDPHP Medicare Advantage plans are now sold only as HMOs after the carrier dropped its PPOs for 2026. Before you commit to any of it, check what is changing next year in our guide to Medicare Advantage plan changes for 2027.