Once you have Original Medicare (Parts A and B), you face a fork in the road. You can add a Medigap (Medicare Supplement) policy, or you can switch your coverage over to a Medicare Advantage (Part C) plan. They are very different animals, and anyone who tells you one is simply “better” is skipping the only question that matters: better for whom? Let's break down what each actually does.

First, the core difference

  • Medigap works alongside Original Medicare. You keep Original Medicare, and the Medigap policy pays the out-of-pocket costs Medicare leaves behind — deductibles, copays, coinsurance. It does not replace Medicare.
  • Medicare Advantage (Part C) is another way to receive your Medicare Part A and Part B benefits. It's offered through a Medicare-approved private insurance company that administers your coverage. Plan networks, cost-sharing, and coverage rules vary by plan — including which doctors you can see, what you pay, and whether you need prior approval for treatments.

That's the fundamental split: Medigap supplements Original Medicare, while Medicare Advantage is another way to receive your Part A and Part B benefits through a private insurer.

The doctor question

This is often the deciding factor:

  • Medigap: You can see any doctor or hospital in the country that accepts Medicare — no networks, no referrals. Great if you travel, split time between states, or want to keep a specific specialist.
  • Medicare Advantage: You generally must use the plan's network (usually an HMO or PPO), and you may need referrals and prior authorizations. Networks can also change mid-year — a doctor who's in-network today might not be next month.

The cost question — and the real risk to understand

Here's where it gets counterintuitive, because “cheaper premium” and “cheaper overall” aren't the same thing.

  • Medigap usually has higher monthly premiums, but far more predictable costs. Medigap policies help pay certain out-of-pocket costs left by Original Medicare — benefits vary by standardized Medigap plan type and applicable state requirements — so you're less likely to face big surprise bills.
  • Medicare Advantage often has low or even $0 monthly premiums, plus a yearly cap on your out-of-pocket costs. But you pay copays as you go, and your costs can climb toward that annual maximum if you need a lot of care.

Here's the real risk to understand: Original Medicare (Part A and Part B) does not have an annual out-of-pocket maximum. That means there's no cap on what you could pay in cost-sharing during a year with a serious illness or hospitalization — the costs can keep adding up. This is one of the main reasons many people add a Medigap policy or choose a Medicare Advantage plan, both of which put some limit on your annual out-of-pocket costs (the specifics vary by plan). Medicare Advantage builds that cap in directly, but in exchange for network rules.

Extra benefits

  • Medicare Advantage frequently includes prescription drug coverage plus extras — dental, vision, hearing, gym memberships, over-the-counter allowances. This is a big part of its appeal.
  • Medigap policies generally do not include coverage for dental, vision, hearing, or prescription drugs — you'd add a separate Part D plan, and typically buy dental/vision/hearing coverage separately if you want it. Benefits vary by standardized Medigap plan type and applicable state requirements.

The catch most people don't hear about

Here's a critical, often-unmentioned point: switching from Medicare Advantage back to Medigap later isn't guaranteed. If you start on Medicare Advantage and try to move to Medigap down the road, insurers can require medical underwriting — meaning they can deny you or charge more based on your health. Your best, guaranteed shot at Medigap (no health questions) is during your Medigap Open Enrollment Period — the 6 months after you enroll in Part B at 65. Miss that window, and getting Medigap later may be harder. This is why the initial choice deserves real thought, not just a glance at the premium.

So which is right for you?

There's genuinely no universal answer — it depends on your priorities:

  • Lean Medigap if: you value seeing any doctor anywhere, want predictable costs, travel often, or want to lock in guaranteed coverage while you're healthy.
  • Lean Medicare Advantage if: you want lower monthly premiums, like having drug and extra benefits bundled in, are comfortable with a network, and want a built-in out-of-pocket cap.

Both are legitimate, popular choices — over half of eligible beneficiaries now choose Medicare Advantage, while many others prefer the freedom of Medigap. The “right” answer depends on your doctors, your budget, your health, and how you like to travel.

This is the single decision I'd most encourage people not to make alone or on a friend's recommendation — because the best choice for your neighbor may be the wrong one for you, and the initial choice can be hard to undo. Walking through your doctors, medications, and priorities is exactly what makes it clear.