Medicare Advantage vs. Medigap: Why the Choice Can Be Hard to Undo

Most Medicare decisions come with a do-over. Pick a drug plan you don’t like and you can change it next fall. Join a Medicare Advantage plan with the wrong network and you can move to another one between October 15 and December 7, or again between January 1 and March 31. You get another try every year.

One decision doesn’t work that way. When you first go on Medicare, you choose between two roads. On one, you join a private Medicare Advantage plan. On the other, you stay in Original Medicare and buy a Medigap policy, also called Medicare Supplement Insurance, to pay the bills Medicare leaves behind. You can go from Medigap to Medicare Advantage in any fall enrollment period with one phone call.

Going the other way is much harder. Outside a few protected situations, federal law doesn’t require a Medigap insurer to sell you a policy, and in most states the company can ask about your health, check your prescription history, and then charge you more or turn you down. KFF, the health policy research group, estimated that 9 in 10 Medicare Advantage enrollees 65 and older, about 22.4 million people as of 2022, had no guaranteed right to buy Medigap once their first-year trial period (a one-time chance to switch back, explained below) was over.

At 65, the choice can feel routine. It’s often made in a few minutes, because one option shows a $0 premium. A decade later it can become nearly permanent, usually just when health has changed and Medigap has started to look better.

Medicare Advantage may still be the right choice for you. Just pick it knowing which way the door swings.

Two roads, side by side

Both options start in the same place. You have Part A and Part B, and you pay the Part B premium, $202.90 a month in 2026.

Medicare Advantage replaces how you get that coverage. A private insurer runs it, usually with a network of doctors and hospitals and its own rules about approvals. More than half of eligible people have chosen it: 35.2 million in 2026, or 55%, by KFF’s count. Two-thirds of the plans with drug coverage charge no premium of their own, and nearly all include some dental, vision and hearing benefits.

Original Medicare with Medigap keeps the government as your insurer. Medicare pays its share and the Medigap policy pays most or all of the rest. You can see any provider in the country that takes Medicare, and you rarely need permission first. You buy a separate Part D plan for prescriptions. About 12.5 million people had a Medigap policy in 2023, according to KFF.

Medigap plans are named by letter, and the letters have nothing to do with Medicare Parts A, B and D. The table uses Plan G, the most common. Premiums are KFF national averages. The Plan G figure is older than the rest because it’s the latest KFF has, so today’s quotes may run higher.

The trade-off is right there in the numbers. With Medigap you pay more every month, whether you see a doctor or not. With Medicare Advantage you pay little up front and more when you use your coverage.

In this example, Plan G plus a drug plan costs about $200 a month more in premiums than a $0 Medicare Advantage plan, or about $2,400 a year. In a bad year, an Advantage plan’s in-network out-of-pocket limit can be as high as $9,250 (the 2026 federal cap).

So why would anyone want to switch back?

People rarely leave a $0 plan while they’re healthy. The wish tends to show up with a serious diagnosis, a specialist who’s out of network, a string of prior authorization requests (the plan’s sign-off before care), or a move across state lines to be closer to family. Those are the same moments when a Medigap insurer is most likely to charge more or say no.

KFF’s analysis lists conditions that can lead to a denial, among them diabetes with complications, congestive heart disease, cancer and asthma. Each company sets its own rules, though, and a person turned down by one insurer may be accepted by another. Some conditions lead to a higher price rather than a flat no.

There are exceptions, and a few of them are wider than people expect. If you’re choosing for the first time, or you’re already in Medicare Advantage and want to know whether the door’s still open, read the next part slowly.

When you can buy Medigap without health questions

In these situations an insurer has to sell you a policy no matter your health. The first four are federal and apply everywhere. The last depends on where you live.

1. Your six-month Medigap Open Enrollment Period. It starts the first day of the month in which you’re 65 or older and also enrolled in Part B. For six months, any Medigap insurer in your state has to sell you any policy it offers, at the same price it charges people in good health. It’s the broadest protection you’ll ever get, and it comes only once.
2. The 12-month trial right, if you’re new to Medicare. If you joined a Medicare Advantage plan when you first became eligible for Medicare at 65, you can leave within the first 12 months, go back to Original Medicare and buy a Medigap policy with guaranteed issue (the insurer must sell it to you regardless of your health).
3. The 12-month trial right, if you dropped Medigap. If you dropped a Medigap policy to try Medicare Advantage for the first time, you can go back within 12 months. You’re entitled to your old policy if the company still sells it, and otherwise to one from a set list of plans.
4. Your plan leaves, or you do. If your Medicare Advantage plan stops serving your area, or you move out of its service area, you have a guaranteed right to buy Medigap Plan A, B, C, D, F, G, K or L from any insurer selling in your state. You can apply as early as 60 days before your coverage ends and no later than 63 days after. A similar right applies when employer or union coverage that works with Medicare ends. Plans C and F are limited to people who became eligible for Medicare before 2020.
5. Your state goes further. KFF counts four states that require insurers to sell Medigap to people 65 and older regardless of health. Connecticut, Massachusetts and New York do it all year or during a set window each year. Maine has a one-month window each year, and it covers Plan A. Minnesota has since passed a law adding an annual window for people 65 to 70. At least nine states have a “birthday rule” or similar window that lets people who already have Medigap switch to another policy without health questions. Those rules help you shop among Medigap policies, but they generally won’t get you a first policy coming out of Medicare Advantage. Other states have their own twists, so ask your state insurance department what it offers.

While you’re applying, two habits keep you from getting stuck.

• Apply first, leave second. Your Medicare Advantage plan stays put until a written approval from the Medigap insurer is in your hands. When it comes, set the Medigap start date for the day your Advantage coverage ends, so there’s no gap.
• One no isn’t the final answer. Each company writes its own underwriting rules. A broker who works with several Medigap insurers tends to know which ones are tougher on which conditions.

Timing matters too. Unless one of the protected situations above applies to you, leaving Medicare Advantage has to happen in an enrollment period: October 15 to December 7, or January 1 to March 31. Line the Medigap approval up so it lands inside one of them.

Shopping for a Medigap policy

Medigap is odd among insurance products. The benefits are standardized by letter, so Plan G from one company pays exactly what Plan G from another pays. In most states the only differences are the price, how the price changes over time and the company’s service, so the whole shopping job comes down to finding a company whose price you can live with today and whose increases over the next ten or fifteen years you can live with too. Massachusetts, Minnesota and Wisconsin use their own standard designs.

Plan G is the most popular Medigap plan; KFF found it covered 39% of all policyholders in 2023. It pays everything Original Medicare leaves behind except the Part B deductible. Plan N has a lower premium in exchange for small copays at office and emergency room visits. A high-deductible version of Plan G costs much less a month and comes with a deductible of a few thousand dollars.

When you request Medicare Supplement quotes, ask each company three questions.

• What’s the monthly price for my age and ZIP code today? Quotes for the same plan in the same ZIP code can be far apart. As a yardstick, KFF put the 2023 average for Plan G at $164 a month. State averages ran from $140 at the low end to $236 at the top.
• How is the policy priced? Medicare’s official Medigap guide describes three methods. Under community rating, everyone pays the same no matter how old they are. Issue-age pricing is set by how old you were when you bought. Attained-age policies start cheaper and climb as you get older, which is why the cheapest quote at 65 is often one of them.
• What have the rate increases been over the last several years? A good agent will have the history, and your state insurance department may publish it.

While you’re on the phone, ask whether there’s a household discount and whether paying yearly or by bank draft changes the price. Then think past this year. Moving to a cheaper company later isn’t easy, since outside the state rules above it means going through underwriting again, so I’d weigh a company’s rate history about as heavily as its starting price.

If you pick Medicare Advantage

For many people it’s the right call. Lower premiums are the obvious draw, and a $2,400 yearly difference is real money in a household budget. Less obvious is the out-of-pocket maximum, which puts a ceiling on your bills that Original Medicare alone doesn’t. The extras count too, if you actually use them.

Before you sign, find out whether your doctors and preferred hospital are in the network for the coming year. Then picture a hard year, one where a hospital stay, a string of specialist visits and months of follow-up care all land on top of your regular bills. Could you cover the out-of-pocket maximum? Add the hospital copay per day to that math. None of these numbers stays put, which is why the Annual Notice of Change that shows up every September deserves a careful read.

Still inside your first 12 months? Put the end date of your trial right on the calendar, because until that date you can change your mind with no health questions asked.

Mistakes to avoid

Don’t judge a plan by its $0 premium alone. The copays and the out-of-pocket limit decide what a bad year costs.

Then there’s the belief that you can always go back. In most states you can apply, sure. The insurer can also say no.

Don’t cancel anything before you’re approved. One coverage shouldn’t end until the next is confirmed in writing.

Still working at 65, with an employer plan, and holding off on Part B? Your six-month Medigap window waits for you. It starts when your Part B starts, not on your 65th birthday, so that’s the date to track.

Your own state may offer more. A short call to its insurance department or to a free State Health Insurance Assistance Program (SHIP) counselor can turn up rights the federal rules don’t mention.

Past your trial window and not sure where you stand? Ask two or three Medigap insurers for quotes and an application well before December 7, the nearest deadline, so an approval can come through in time. If you miss it, the January 1 to March 31 window is next. It costs nothing to ask, and their answers will show whether going back is still an option.