Quick answer: Medicare Advantage (Part C) usually has a low or $0 monthly premium but you pay copays as you use care, must stay in a network, and need referrals and prior authorisation for many services. Medigap (Supplement) costs $100 to $300+ a month on top of Part B but covers most out-of-pocket costs, works with any doctor who accepts Medicare, and needs no referrals. Advantage generally shifts cost from premiums to the point of care; Medigap generally shifts it the other way. Which trade-off fits depends on your health, travel patterns and budget. The timing trap: switching from Advantage to Medigap later can require medical underwriting, and you may be refused.
The structural difference
Medicare Advantage does not replace Medicare. You remain in Medicare, but a private insurer delivers your Part A and Part B coverage instead of Original Medicare, usually bundling drug coverage and extras like dental and vision, and running it like an HMO or PPO with networks and prior authorisation.
Medigap adds to Original Medicare. You keep Parts A and B, buy a separate Part D drug plan, and the Medigap policy pays the deductibles, copays and coinsurance Original Medicare leaves behind. There is no network because Original Medicare has none.
Side by side
| Medicare Advantage | Medigap + Part D | |
|---|---|---|
| Monthly premium | Often $0, but varies by plan (plus the $202.90 Part B premium) | Varies by plan letter, state, insurer and age (plus Part B and Part D premiums) |
| Costs when you use care | Copays and coinsurance up to an annual out-of-pocket maximum | Little to nothing with Plan G or N |
| Doctor choice | Network only; out-of-network costs more or is not covered | Any provider in the US who accepts Medicare |
| Referrals | Often required (HMO plans) | Never |
| Prior authorisation | Common for imaging, surgery, skilled nursing | Rare under Original Medicare |
| Drug coverage | Usually included | Separate Part D plan required |
| Extras (dental, vision, hearing, gym) | Often included | Not included; buy separately |
| Travel within the US | Limited outside the service area | Works nationwide |
| Foreign travel emergency | Rare | Included in several Medigap plans |
| Annual out-of-pocket cap | Yes, capped by law | Only Plans K and L have a cap; with Plan G your remaining exposure is effectively just the Part B deductible |
The real cost comparison
Advantage looks cheaper monthly and can be more expensive in a bad year; Medigap costs more monthly and is predictable. A rough illustration for one year:
| Healthy year | Year with surgery and rehab | |
|---|---|---|
| Advantage ($0 premium) | A few hundred dollars in copays | Copays and coinsurance up to the plan out-of-pocket maximum, which varies by plan and can run into the thousands |
| Medigap Plan G ($150/mo) | About $1,800 in premiums plus the $283 Part B deductible (2026) | About $1,800 in premiums plus the $283 Part B deductible (2026) |
That is the trade in one line: Advantage transfers cost from healthy years to sick years, and Medigap spreads it evenly. Which is better depends on how much financial variability you can absorb, not on which is cheaper on paper.
The enrolment timing trap
This is the part people learn too late. During your Medigap open enrolment period, the six months beginning on the first day of the month in which you are both 65 or older and enrolled in Part B, insurers must sell you any Medigap policy at the standard price regardless of your health.
After that window closes, in most states insurers can require medical underwriting. If you start with Advantage and later develop a condition and want to switch to Medigap, you can be charged more or declined entirely. A handful of states have rules allowing switching without underwriting, but most do not. Federal guaranteed issue rights still apply in defined situations regardless of your state — including a trial right if you joined Advantage and want to return to Original Medicare, and when your plan leaves your service area. These windows generally run from 60 days before your coverage ends to no more than 63 days afterwards, so check whether one applies to you before assuming you are stuck.
You can switch from Medigap to Advantage at any open enrolment. Going the other direction is the hard one. That asymmetry is the single most important thing to understand before choosing.
Who each option suits
| Situation | What to weigh |
|---|---|
| Healthy, on a tight budget, stays local | Advantage |
| Chronic conditions or frequent specialist visits | Medigap |
| Splits the year between two states, or travels widely | Medigap |
| Wants dental, vision and hearing bundled | Advantage |
| Wants a predictable monthly cost and no surprise bills | Medigap |
| Has a preferred doctor or hospital | Check the network first; Medigap if they are out of network |
| Qualifies for both Medicare and Medicaid | Advantage, often a Dual Eligible Special Needs Plan |
Questions to ask before enrolling
- Are my doctors and my preferred hospital in the plan network, confirmed with the provider directly, not just the directory?
- Are my prescriptions on the formulary, and in which tier?
- What is the plan annual out-of-pocket maximum?
- Which services require prior authorisation?
- If Medigap: which lettered plan, and how has this insurer raised premiums historically?
- What happens if I move to another state?
Frequently asked questions
Can I have both Advantage and Medigap?
No. Medigap only works with Original Medicare. If you are in a Medicare Advantage plan, it is illegal for anyone to sell you a Medigap policy unless you are switching back to Original Medicare.
Are Medigap plans the same across insurers?
Benefits for a given letter plan are standardised by law, so Plan G from one insurer covers the same as Plan G from another. Only the price and service differ, which means shopping on price is rational.
When can I switch plans?
Medicare open enrolment runs 15 October to 7 December each year. There is also a Medicare Advantage open enrolment period from 1 January to 31 March, but it is only open to people already in an Advantage plan: it lets you move to a different Advantage plan, or back to Original Medicare with a separate drug plan. It cannot be used to join Advantage from Original Medicare. Moving to Medigap outside a protected window may require underwriting.
Does Advantage cover me while travelling?
Usually only for emergencies outside the service area. Routine care away from home is generally not covered, which is why frequent travellers lean toward Medigap.
Last updated September 2026. Plan availability, premiums and state rules on Medigap underwriting vary; verify on medicare.gov or with your State Health Insurance Assistance Program (SHIP), which gives free unbiased counselling. General information, not insurance advice.
Sources
Figures and rules in this article come from official Medicare and CMS publications: Medicare costs (2026 Part B premium and deductible), Understanding Medicare Advantage Plans, Choosing a Medigap Policy, When can I buy a Medigap policy? and CMS CY2026 out-of-pocket limits for Medigap Plans K and L. Medicare figures change every calendar year. This article is general information, not advice on which plan to choose — for free personalised help, contact your State Health Insurance Assistance Program.
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