At 65, you face a Medicare decision that most people don’t anticipate: do you stay with Original Medicare — the federal Parts A and B program — and potentially add a Medigap supplement, or do you switch to Medicare Advantage, a private-plan alternative that replaces Original Medicare entirely? The choice has long-term consequences that are hard to undo, and in most states, switching later is harder than it looks.
As of 2026, 55% of eligible Medicare beneficiaries — approximately 35 million people — are enrolled in Medicare Advantage, according to KFF. But majority preference isn’t a reason to choose anything. The right call depends on your health, provider relationships, budget, and geography.
How Original Medicare works
Original Medicare is the federal program directly administered by the Centers for Medicare & Medicaid Services (CMS). It has two core parts:
Part A covers inpatient hospital stays, skilled nursing facility care, hospice, and some home health care. Most people qualify for premium-free Part A if they — or their spouse — paid Medicare taxes for at least 40 quarters (10 years). Part A carries a per-benefit-period hospital deductible of $1,736 in 2026, per the CMS 2026 Medicare Parts B Premiums and Deductibles fact sheet, plus daily coinsurance of $434 for days 61–90 of a hospital stay. There is no annual cap on Part A deductibles.
Part B covers doctor visits, outpatient services, preventive care, and durable medical equipment. The standard monthly premium is $185.00 in 2026. The annual Part B deductible is $283. After the deductible, Original Medicare pays 80% of most approved outpatient services — you pay the remaining 20% with no annual out-of-pocket ceiling. A single major illness or surgery can expose you to tens of thousands of dollars in uncapped 20% coinsurance.
This is why most Original Medicare beneficiaries add either a Medigap (Medicare Supplement) policy, a standalone Part D prescription drug plan, or both. Medigap is private insurance standardized into plan letters (A through N in most states) that fills Original Medicare’s cost-sharing gaps. For a full primer on Medigap plan types, see our guide here.
How Medicare Advantage works
Medicare Advantage (Part C) is offered by private insurers under contract with CMS. When you enroll, you replace Original Medicare with the private plan — which must cover at least everything Original Medicare covers, and typically does more.
Key structural features:
- Annual out-of-pocket maximum. CMS requires all MA plans to cap your annual in-network costs. Per KFF’s 2026 Medicare Advantage analysis, the 2026 average in-network OOP maximum is $5,421, with a federal ceiling of $9,250 in-network and $13,900 combined in/out-of-network.
- Low or $0 monthly premiums. 75% of MA enrollees pay no supplemental premium beyond the standard Part B premium ($185/month you still owe regardless), per KFF 2026 data.
- Bundled prescription drug coverage. Most MA plans include Part D, so you don’t need a separate drug plan.
- Extra benefits. Per KFF 2026 data, 99%+ of MA enrollees have access to vision coverage, 98% to dental, 95% to hearing benefits, and 91% to fitness program benefits.
- Network restrictions. Most MA plans are HMO or PPO structures. HMO plans require in-network providers and usually require referrals for specialist visits. PPO plans allow out-of-network care at higher cost.
- Prior authorization. Per KFF, 99% of MA enrollees are in plans requiring prior authorization for at least some services. In 2024, MA plans issued nearly 53 million prior authorization requests and denied 7.7% — about 4.1 million. Of those denied, 80%+ were overturned on appeal — but only 11.5% of denied requests were ever appealed.
Side-by-side comparison
| Original Medicare | Medicare Advantage | |
|---|---|---|
| Provider access | Any Medicare-accepting provider nationwide | Network-based (HMO or PPO) |
| Monthly premium | $185 Part B + Medigap ($100–$300+/mo) | $185 Part B + often $0 plan premium |
| Annual OOP cap | None — unlimited exposure | Required — avg $5,421 in-network (2026) |
| Prescription drugs | Requires separate Part D plan | Usually bundled |
| Dental / Vision / Hearing | Not covered | Usually included |
| Prior authorization | Rarely required | Required for most services |
| Referrals required | No | Yes (HMO); optional (PPO) |
| Multi-state / travel use | Nationwide, any provider | Typically limited to service area |
| Medigap compatible | Yes | No |
The network trade-off
Original Medicare’s most practical advantage is provider flexibility. You can see any doctor, specialist, or hospital that accepts Medicare — anywhere in the U.S., without a referral. For people with established specialist relationships, complex conditions, or significant travel patterns, this access is material.
Medicare Advantage networks limit that flexibility. An HMO plan that looks attractive at enrollment may require a new primary care physician, referrals before every specialist visit, and prior authorization for procedures. If you split time between states or travel frequently, most HMO-based MA plans provide in-network coverage only in your home service area — emergency care is typically covered nationally, but routine care generally is not.
The prior authorization picture warrants attention. While most requests are eventually approved, the appeal process requires time and documentation. For someone navigating a serious diagnosis, that burden can be significant.
The Medigap window you cannot get back
Here is the consequence that catches many people off guard: if you choose Medicare Advantage at 65 and later want to switch to Original Medicare with Medigap, you may not be able to get Medigap at any price.
The federal Medigap open enrollment window — during which insurers must cover you regardless of health history — is six months long, beginning when you are both 65 or older and enrolled in Part B. That window doesn’t repeat each year. After it closes, in most states, Medigap insurers can use medical underwriting and deny applications based on pre-existing conditions.
Per KFF analysis, 90% of Medicare Advantage enrollees age 65+ — approximately 22.4 million people — lack guaranteed issue rights to buy Medigap because the federal trial period protection has expired. Only four states — Connecticut, Massachusetts, Maine, and New York — require Medigap insurers to offer coverage on guaranteed-issue terms beyond the initial federal window.
If you develop a serious health condition while in Medicare Advantage and then try to switch to Original Medicare with Medigap, you may find yourself locked out of Medigap in your state — and exposed to Original Medicare’s uncapped 20% coinsurance with no supplement available.
This is the most consequential asymmetry of the initial Medicare choice. For more on enrollment windows and how to avoid permanent premium penalties, see Medicare Enrollment in 2026: Windows, Penalties, and What to Do at 65.
Who each option fits
Original Medicare + Medigap tends to fit when:
- You have established specialists or medical teams you want to keep
- You travel frequently or spend time in multiple states seasonally
- You have or anticipate complex, ongoing health needs
- Predictable costs matter more than low monthly premiums
- You live in a rural area with limited MA plan options
Medicare Advantage tends to fit when:
- Low or $0 monthly premiums are a priority and you’re comfortable with the annual OOP max as your worst-case exposure
- You want bundled dental, vision, and hearing coverage without managing separate plans
- Strong, high-rated plans (4–5 stars) are available in your zip code
- Your health is generally good and you use healthcare infrequently
- The ongoing Medigap premium is a financial stretch
Medicare.gov offers a plan-finder tool that lets you compare specific plans in your zip code by premium, OOP maximum, star rating, drug formulary, and extra benefits. Your State Health Insurance Assistance Program (SHIP) offers free, unbiased plan comparisons from local counselors.
For related coverage decisions, see Long-Term Care Insurance: What It Covers and When to Buy (2026).
This content is educational and does not constitute health insurance or financial advice. Medicare premiums, deductibles, enrollment windows, and plan details change annually. Verify current figures at medicare.gov and cms.gov before making enrollment decisions.
