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Once you have Medicare Parts A and B, you face one big decision. Original Medicare leaves you with 20 percent coinsurance on Part B services and no annual limit on what you can owe. Two different products exist to plug that hole: Medicare Advantage and Medigap. They solve the same problem in opposite ways, and the right answer depends on how you use health care, where you live, and how much predictability you want in your budget.
What each one actually is
Medigap (also called Medicare Supplement insurance) is a private policy that sits on top of Original Medicare. Medicare pays its share first, then your Medigap policy pays most or all of the rest, depending on the plan letter. You keep Original Medicare, which means any doctor or hospital in the country that accepts Medicare. No networks, no referrals.
Medicare Advantage is a replacement for the way your Medicare benefits are delivered. A private insurer contracts with Medicare to provide your Part A and Part B coverage, usually bundled with Part D drug coverage and extras like dental, vision, and hearing. You use the plan’s network of doctors and hospitals, and the plan sets its own cost-sharing rules.
One hard rule: you cannot have both. Medigap policies only work with Original Medicare. If you join a Medicare Advantage plan, a Medigap policy cannot pay your Advantage copays or deductibles, and it is illegal for an insurer to sell you one.
The cost tradeoff
Medicare Advantage usually wins on monthly premiums. Many plans charge no premium beyond the Part B premium you already pay ($202.90 per month in 2026), though some charge an additional amount. Medigap costs more per month because it covers more. A typical Medigap premium runs in the low hundreds per month depending on the plan letter, your age, your zip code, and the insurer, and you still need a separate Part D drug plan with its own premium.
But the premium is only half the story. Medicare Advantage plans charge copays and coinsurance when you use care, and while they cap your annual out-of-pocket spending, the cap can be several thousand dollars. Medigap Plan G, the most popular choice for people who became eligible after 2020, covers nearly everything except the Part B deductible ($283 in 2026). After that, your medical costs for the year are close to zero.
So the tradeoff is straightforward. Medicare Advantage: lower fixed monthly cost, higher and less predictable costs when you get sick. Medigap: higher fixed monthly cost, very low and predictable costs when you get sick.
The network tradeoff
This is where the decision often gets made. Medigap travels with Original Medicare, which means any provider in the US that accepts Medicare. If you split your time between two states, travel frequently, or want a specific specialist at a major medical center, Medigap gives you that freedom without referrals.
Medicare Advantage plans run networks. HMO-style plans generally require you to stay in network except for emergencies, and many require referrals to see specialists. PPO-style plans let you go out of network but charge you more for it. Networks can also change from year to year, so the plan that includes your cardiologist this year might not next year. If your doctors are all local and you rarely travel, a network may never bother you. If provider choice matters to you, it will.
The health tradeoff nobody mentions early enough
Medigap has a timing trap. When you first become eligible for Medicare, you get a six-month Medigap open enrollment period during which insurers must sell you any policy at the best available rate, regardless of your health. After that window closes, insurers in most states can use medical underwriting. That means they can deny you or charge you more based on pre-existing conditions.
This matters because many people choose Medicare Advantage at 65 when they are healthy, then want to switch to Medigap years later when health problems appear. In most states, that switch requires passing underwriting, and the people who most want Medigap are the least likely to qualify. Some states (New York and Connecticut, for example) have year-round guaranteed issue rights, but they are the exception.
Medicare Advantage, by contrast, accepts everyone during the annual open enrollment period regardless of health. You can move between Advantage plans every year with no underwriting.
Drug coverage and extras
Most Medicare Advantage plans include Part D prescription drug coverage, so you get medical and drug coverage in one plan with one set of rules. With Medigap, you buy a separate Part D plan, which means a separate premium, a separate formulary to check, and a separate set of pharmacy rules.
Advantage plans also tend to bundle dental, vision, hearing, and fitness benefits. The coverage is usually basic (cleanings and exams rather than implants, for example), but it is more than Original Medicare offers, which is close to nothing for these services. If you want dental coverage with Medigap, you buy a separate standalone dental plan.
Which one fits which person
Medicare Advantage tends to fit people who are relatively healthy, take few prescriptions, are comfortable using a local network, want one plan that handles everything, and prefer lower monthly premiums even if it means copays when they need care.
Medigap tends to fit people who want to see any doctor anywhere without referrals, travel or live in two places, have ongoing health conditions or expect significant medical spending, and would rather pay more each month for costs they can predict.
There is also a middle path worth knowing about. High-deductible Medigap Plan G offers much lower premiums in exchange for a high annual deductible you pay before the policy starts covering costs. It suits people who want Medigap’s provider freedom and catastrophic protection but are healthy enough to self-insure the smaller bills.
How to compare before you decide
Start with your doctors. Call each one and ask which Medicare Advantage plans they accept, because online directories go stale. Then look at your prescriptions and check each plan’s formulary, since drug coverage differences can easily outweigh premium differences.
Next, run the math for a bad year, not a good one. Add up the annual premium plus the plan’s out-of-pocket maximum. That is your worst case. For Medigap Plan G, the worst case is roughly the annual premium plus the Part B deductible. For an Advantage plan, it is the annual premium plus the out-of-pocket max. Compare those two numbers. The answer is often clearer than the marketing suggests.
Finally, remember the decision is not equally reversible. You can move from Medigap to Medicare Advantage every fall during open enrollment with no health questions. Moving the other direction usually requires underwriting. If you are torn, that asymmetry is worth weighing. The Medicare parts guide covers how each piece works if you want the full picture first.
