The Gap Original Medicare Leaves Behind
Original Medicare (Parts A and B) covers a lot — but not everything. It doesn't cover most prescription drugs, dental, vision, or hearing. And it has no out-of-pocket maximum, which means a serious illness could cost you tens of thousands of dollars in a single year. To fill these gaps, most Medicare beneficiaries choose one of two paths: a Medicare Supplement plan (also called Medigap) or a Medicare Advantage plan (Part C). Both approaches have real advantages — and real trade-offs. The right choice depends on your health, your finances, and how you use healthcare.
What Is Medicare Supplement (Medigap)?
A Medicare Supplement plan is a private insurance policy that works alongside Original Medicare. It pays for costs that Medicare doesn't cover — like your Part A hospital deductible, Part B coinsurance, and excess charges. Medigap plans are standardized by the federal government: a Plan G from one company covers exactly the same benefits as a Plan G from another company. The only difference between companies is the premium. Because Medigap works with Original Medicare, you can see any doctor or hospital in the country that accepts Medicare — no networks, no referrals, no prior authorizations for covered services.
Pro tip: Plan G is currently the most comprehensive Medigap plan available to new Medicare enrollees (Plan F was discontinued for new enrollees in 2020). It covers everything except the Part B deductible, which is $257 in 2025.
What Is Medicare Advantage (Part C)?
Medicare Advantage is an alternative to Original Medicare offered by private insurance companies. Instead of using Medicare directly, you get your Part A and Part B benefits through the Advantage plan — and most plans also include Part D drug coverage and extras like dental, vision, and hearing. Medicare Advantage plans typically have lower monthly premiums than Medigap (some are $0 premium), but they use provider networks (HMO or PPO) and often require prior authorizations for certain services. Your out-of-pocket costs depend on how much care you use, up to an annual maximum.
Pro tip: A $0 premium Medicare Advantage plan isn't free — you still pay your Part B premium ($185/month in 2025), and you'll have copays and coinsurance when you use care. The out-of-pocket maximum (up to $9,350 in-network in 2025) is the real cost ceiling to watch.
Cost Comparison: Premiums vs. Out-of-Pocket
Medigap plans have higher monthly premiums — typically $100–$250/month depending on your age, location, and plan — but very predictable out-of-pocket costs. With Plan G, once you've met the Part B deductible, you pay nothing for Medicare-covered services. Medicare Advantage plans have lower (sometimes $0) premiums but variable out-of-pocket costs based on usage. If you're healthy and rarely use healthcare, Advantage may cost less overall. If you have ongoing health conditions or use specialists frequently, Medigap's predictability often makes it the better financial choice.
Pro tip: Run the math both ways. Add up your Medigap premium for the year, then compare it to your estimated out-of-pocket costs under an Advantage plan based on your typical healthcare usage. The break-even point is usually around 3–5 specialist visits or one hospitalization per year.
Provider Access: Networks vs. Nationwide Freedom
This is often the deciding factor. With Medigap + Original Medicare, you can see any doctor or go to any hospital in the US that accepts Medicare — no referrals, no network restrictions. This matters enormously if you travel frequently, split time between states (snowbirds), see specialists at major medical centers, or simply want the freedom to choose your own providers. Medicare Advantage plans use HMO or PPO networks. HMOs require you to use in-network providers and get referrals for specialists. PPOs offer more flexibility but still have higher costs for out-of-network care. If your preferred doctors aren't in the plan's network, you may need to switch providers.
Pro tip: If you spend winters in Florida and summers in another state, Medigap is almost always the better choice. Most Medicare Advantage plans only cover out-of-network care for emergencies — routine care in your other state would be out-of-pocket.
Prescription Drug Coverage
Medigap plans do not include prescription drug coverage — you need to add a standalone Part D plan separately. Most Medicare Advantage plans include Part D drug coverage built in. If you choose Medigap, you'll pay two premiums: one for the Medigap plan and one for Part D. If you choose Medicare Advantage with drug coverage, it's bundled into one plan. The trade-off: standalone Part D plans can sometimes be optimized more precisely for your specific medications, while Advantage drug coverage is tied to the plan's overall formulary.
Pro tip: If you're leaning toward Medigap, use Medicare's Plan Finder at medicare.gov to compare standalone Part D plans based on your exact medications before you finalize your decision. Factor that premium into your total cost comparison.
Enrollment Timing: When You Can Switch
Your best window to enroll in Medigap is during your 6-month Medigap Open Enrollment Period, which starts the month you turn 65 and are enrolled in Part B. During this window, insurers must accept you regardless of health conditions and can't charge you more based on pre-existing conditions. After this window, you may be subject to medical underwriting — meaning you could be denied or charged more based on your health history. Medicare Advantage plans can be switched annually during the October 15 – December 7 Annual Enrollment Period, with no medical underwriting required.
Pro tip: If you're approaching 65, don't delay enrolling in Medigap. The 6-month guaranteed issue window is your best — and sometimes only — chance to get comprehensive coverage without medical underwriting.
Side-by-Side Comparison
| Feature | Medicare Supplement (Medigap) | Medicare Advantage |
|---|---|---|
| Monthly Premium | Higher ($100–$250+) | Lower (often $0–$50) |
| Out-of-Pocket Costs | Very predictable, near $0 with Plan G | Variable; capped at annual maximum |
| Provider Network | Any Medicare-accepting provider nationwide | In-network required (HMO) or preferred (PPO) |
| Referrals Required | No | Yes (HMO) / No (PPO) |
| Drug Coverage | Separate Part D plan required | Usually included |
| Dental/Vision/Hearing | Not included | Often included |
| Travel / Multi-State | Excellent — nationwide coverage | Limited — emergency only out-of-network |
| Switching Plans | May require medical underwriting | Annual enrollment, no underwriting |
Which Should You Choose?
- Choose Medigap if you want predictable costs, nationwide provider access, or travel frequently.
- Choose Medicare Advantage if you want lower premiums, bundled drug/dental/vision, and are comfortable with a network.
- Enroll in Medigap during your 6-month guaranteed issue window — don't wait.
- If choosing Medigap, add a standalone Part D plan to cover prescriptions.
- Compare total annual costs (premium + expected out-of-pocket), not just monthly premiums.
- An independent broker can compare every plan in your area at no cost to you.