Medigap vs. Medicare Advantage: The Structural Differences That Matter Most
Medigap adds predictable coverage on top of Original Medicare. Medicare Advantage replaces it with a private plan, usually with lower premiums, networks, and an out-of-pocket cap. Here is how they compare and why switching later can be hard.
Once you have Medicare Parts A and B, the biggest choice is how to handle the rest: keep Original Medicare and add a Medicare Supplement (Medigap) policy and a Part D drug plan, or join a Medicare Advantage plan. They work very differently. The choice affects which doctors you can see, how predictable your costs are, and whether you can change your mind later.
The short version
- Medigap works alongside Original Medicare and pays some or most of your share of costs, such as deductibles and the 20% Part B coinsurance. You can generally see any provider nationwide that accepts Medicare. Premiums are higher, but out-of-pocket costs are low and predictable.
- Medicare Advantage replaces Original Medicare with a private plan. Premiums are often low, many plans include drug coverage and extras, and there's an annual out-of-pocket maximum. Most use networks, and many require prior authorization for some services.
- You can't have both at the same time.
- In most states, buying Medigap later can require medical underwriting, so switching from Medicare Advantage back to Original Medicare with Medigap isn't always possible on good terms.
Side by side
| Original Medicare + Medigap + Part D | Medicare Advantage | |
|---|---|---|
| Provider access | Any provider nationwide that accepts Medicare | Usually a network; PPOs allow out-of-network at higher cost |
| Referrals | Not required by Medicare | Often required in HMOs |
| Prior authorization | Rare under Original Medicare | Common for certain services |
| Monthly premiums | Medigap premium + Part D premium | Often low; some $0 (plus Part B premium in both cases) |
| Out-of-pocket costs | Low and predictable, depending on plan letter | Copays and coinsurance up to an annual maximum |
| Annual out-of-pocket limit | No limit in Original Medicare itself; Medigap fills most gaps | Yes, for covered A and B services |
| Drug coverage | Separate Part D plan | Usually included |
| Extras (dental, vision, hearing) | Generally not included | Often included, with limits |
| Travel | Nationwide access; some Medigap plans include limited foreign emergency coverage | Usually limited to network and emergencies outside the area |
| Changing later | Medigap may require underwriting outside protected periods | Can switch plans during annual windows |
How costs compare at different levels of use
A hypothetical comparison for one person's annual costs beyond the Part B premium, which everyone pays. Numbers are illustrative; real premiums and plan designs vary widely by location, age, and plan.
- Medigap path: a Medigap plan at $160 a month, a Part D plan at $40 a month, and a hypothetical $260 Part B deductible that this Medigap plan doesn't cover. About $2,660 a year regardless of how much care is used (drug copays aside).
- Medicare Advantage path: $0 premium, copays and coinsurance as care is used, with a hypothetical $6,000 annual out-of-pocket maximum for medical services.
Show the numbers behind this chart
| Medigap + Part D | Medicare Advantage | |
|---|---|---|
| Low use | $2,660 | $400 |
| Moderate use | $2,660 | $2,000 |
| High use (hits MA maximum) | $2,660 | $6,000 |
In low-use years, Medicare Advantage often costs less. In high-use years, Medigap's predictability can cost less. The comparison is partly about money and partly about which risk you prefer: steady premiums or variable costs with a cap.
Medigap plan letters
In most states, Medigap plans are standardized by letter, such as Plan G or Plan N. A Plan G from one insurer has the same basic benefits as a Plan G from another; premiums, customer service, and pricing methods differ. Three states standardize plans differently. Some plan letters aren't available to people who became eligible for Medicare after a certain date.
Insurers price Medigap in different ways (community-rated, issue-age-rated, or attained-age-rated), which affects how premiums change as you age.
The switching problem
This is the most important structural difference for many people.
- During your Medigap open enrollment period, a one-time six-month window that starts when you're 65 or older and enrolled in Part B, insurers generally must sell you any Medigap plan they offer without medical underwriting.
- After that window, in most states, insurers can use medical underwriting: they can charge more or decline coverage based on health, unless you have a specific guaranteed issue right.
- That means someone who chooses Medicare Advantage at 65 and later wants Original Medicare with Medigap may not be able to buy Medigap at a reasonable price, or at all, depending on health and state law.
Federal rules provide some guaranteed issue rights, including a trial right for people who join a Medicare Advantage plan when first eligible, or who drop Medigap to try Medicare Advantage for the first time, and leave within a limited period. A few states provide broader protections. See Medigap underwriting rules.
Questions that help decide
- Do you want to see specific doctors or hospitals? Are they in the plan's network?
- Do you travel or live in more than one state during the year?
- Would you rather pay higher, predictable premiums or lower premiums with variable costs?
- How much could you comfortably pay in a bad year?
- How do you feel about prior authorization and referrals?
- What are the drug costs for your prescriptions under each option?
- What do your state's Medigap rules allow if you want to switch later?
Free, unbiased help
Your State Health Insurance Assistance Program (SHIP) offers free counseling and can explain the rules in your state. Medicare.gov's plan finder compares plans available where you live.
The takeaway
Medigap pairs broad provider access with predictable, low out-of-pocket costs at higher premiums. Medicare Advantage offers lower premiums, bundled benefits, and an out-of-pocket cap, with networks and plan rules. The decision you make when first eligible matters more than it seems, because buying Medigap later can be difficult in most states.
Sources
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