“Plan C” in Medicare can refer to two completely different things: Medicare Part C (also called Medicare Advantage) or Medigap Plan C (a supplemental insurance policy). These are not the same product, and confusing them can lead to costly enrollment mistakes. Medicare Part C replaces your Original Medicare coverage with a private plan. Medigap Plan C supplements your Original Medicare by filling in gaps like deductibles and coinsurance. You cannot have both at the same time.
Medicare Part C (Medicare Advantage)
Medicare Part C, officially called Medicare Advantage, is an alternative way to receive your Medicare benefits. Instead of getting coverage directly from the federal government through Original Medicare (Parts A and B), you enroll in a plan run by a private insurance company that Medicare has approved. These plans bundle Part A (hospital coverage) and Part B (medical coverage) together, and most also include Part D (prescription drug coverage).
The biggest draw for many people is that Medicare Advantage plans typically offer benefits that Original Medicare does not cover at all. As of 2021, 99% of Medicare Advantage enrollees had access to some vision coverage, 97% had access to hearing benefits including hearing aids, and 94% had access to dental coverage. Original Medicare largely excludes routine dental, vision, and hearing services.
Medicare Advantage plans also come with a yearly cap on what you’ll spend out of pocket, something Original Medicare lacks entirely. In 2025, that cap cannot exceed $9,350 for in-network services or $14,000 when out-of-network services are included. Once you hit that limit, the plan covers 100% of your costs for covered services for the rest of the year.
How Medicare Advantage Networks Work
Medicare Advantage plans come in different structures, and the type you choose determines which doctors you can see and how much flexibility you have.
HMO plans require you to use doctors and hospitals within the plan’s network. You’ll typically choose a primary care provider who coordinates your care and may need to provide referrals before you see a specialist. If you go outside the network, the plan may not cover the cost at all, leaving you responsible for the entire bill.
PPO plans also have a provider network but give you the option to see out-of-network doctors. You’ll pay more for out-of-network care than you would for in-network care, but the plan still covers a portion. PPO plans don’t require referrals to see specialists.
This network tradeoff is one of the most important factors to weigh. If you travel frequently, split time between two states, or want to see specialists without getting approval first, a PPO or sticking with Original Medicare may be a better fit.
Prior Authorization in Medicare Advantage
One common frustration with Medicare Advantage is prior authorization, where your plan must approve certain treatments or services before you receive them. Recent federal rules have tightened how plans can use this process. Plans can now only use prior authorization to confirm a diagnosis or verify that a service is medically necessary. They cannot use it to deny care that would be covered under Original Medicare.
If you switch from one Medicare Advantage plan to another while in the middle of treatment, your new plan must provide at least a 90-day transition period during which it cannot require prior authorization for your ongoing care. Emergency behavioral health services are also exempt from prior authorization entirely. Every Medicare Advantage plan is now required to have a committee that reviews its authorization policies annually to ensure they align with what Original Medicare would cover.
Medicare Advantage Star Ratings
CMS rates Medicare Advantage plans on a one-to-five-star scale using up to 43 quality measures. These cover a wide range of factors: how well the plan manages chronic conditions like diabetes and high blood pressure, how quickly members can get appointments, customer service quality, how often members choose to leave the plan, and how the plan handles appeals. Plans earning five stars get highlighted on the Medicare Plan Finder, while consistently low-performing plans are flagged with a warning icon. Checking star ratings before enrolling is one of the simplest ways to compare plan quality in your area.
When You Can Enroll in Medicare Advantage
You can join, switch, or drop a Medicare Advantage plan during the Annual Open Enrollment Period, which runs from October 15 through December 7 each year. Coverage begins January 1. If you’re already in a Medicare Advantage plan and want to make a change, there’s a second window from January 1 through March 31 called the Medicare Advantage Open Enrollment Period. During this time, you can switch to a different Medicare Advantage plan or drop your plan and return to Original Medicare. You also get a chance to enroll when you first become eligible for Medicare, during your Initial Enrollment Period.
Medigap Plan C (A Different Product Entirely)
Medigap Plan C is a supplemental insurance policy, not a replacement for Original Medicare. If you stay on Original Medicare (Parts A and B), a Medigap policy helps pay the out-of-pocket costs that Original Medicare leaves behind, like coinsurance, copayments, and deductibles. Medigap Plan C was one of the more comprehensive supplement options, covering both the Part A deductible and the Part B deductible along with coinsurance and other gaps.
There’s a critical catch: Medigap Plan C is no longer available to people who became newly eligible for Medicare on or after January 1, 2020. This includes anyone who turned 65 on or after that date, as well as anyone who first qualified for Medicare through disability or end-stage renal disease after that date. The change came from a federal law called MACRA, which also restricted Medigap Plan F for the same reason: both plans covered the Part B deductible, and Congress wanted beneficiaries to have some “skin in the game.”
If you were eligible for Medicare before January 1, 2020, you can still purchase or keep a Medigap Plan C. Existing policyholders are not affected by the restriction. For those who became eligible after that cutoff, the closest alternative is Medigap Plan D, which offers similar coverage but does not pay the Part B deductible.
Choosing Between Medicare Advantage and Medigap
This is one of the most consequential decisions in Medicare, and it comes down to how you prefer to manage costs and access care. Medicare Advantage plans often have low or zero monthly premiums and include extras like dental and vision, but they restrict you to a network of providers and may require prior authorization. Medigap policies paired with Original Medicare give you the freedom to see any doctor who accepts Medicare anywhere in the country, with no network restrictions and no prior authorization, but premiums are higher and you’ll need a separate Part D plan for prescriptions.
The financial math differs depending on how much care you use. If you’re relatively healthy and comfortable staying within a plan’s network, Medicare Advantage can save money. If you have complex health needs, see multiple specialists, or want the certainty that nearly all your out-of-pocket costs are covered regardless of where you go, a Medigap plan may be worth the higher premium.