Medicare Advantage Is a One-Way Door: The 2026 Medigap Trap

Ruth signed up for a Medicare Advantage plan in October 2019, the fall she turned 65. The premium was $0, it came with dental coverage and a $40 monthly grocery card, and for five years it worked exactly as advertised. Then in March 2026 she was diagnosed with a cancer that her plan's oncologist wasn't the right fit for, and by the end of the year she'd hit her plan's out-of-pocket maximum of $9,250. So she did what she assumed she could always do: she tried to leave.

She couldn't. Not the way she wanted to.

That gap between what people think Medicare's annual switching window offers and what it actually offers is the single most expensive misunderstanding in retirement health coverage. Every October, the ads make it sound like you can move freely between plans forever. You can move in freely. Moving back out is where the door sticks.

Here's how the trap works, why 2026 is a good year to understand it, and what to check before you're the one standing on the wrong side of it.

The choice underneath the choice

When you enroll in Medicare, you're really making one big decision, and most people don't realize it's the big one.

Path one is Original Medicare (Parts A and B) plus a Medigap policy, sometimes called a Medicare Supplement. Medigap fills in the deductibles and coinsurance that Original Medicare leaves you on the hook for, so a hospital stay doesn't turn into a five-figure bill. You pay a monthly premium for it. The average among current Medigap policyholders was about $217 a month in 2023, roughly $2,604 a year, according to KFF's analysis of NAIC data.

Path two is Medicare Advantage, run by private insurers. It bundles your medical and usually your drug coverage into one plan, often with a $0 premium and extras like dental, vision, and those grocery or over-the-counter cards. In exchange, you accept a network, referrals, and prior authorization. More than half of eligible Medicare beneficiaries, 55% in 2026, are now in Advantage plans, per KFF.

On paper, you can switch between these two paths every year during the Annual Enrollment Period, October 15 to December 7, with the new plan starting January 1. And in one direction, that's true. You can drop Medigap and Original Medicare and jump into an Advantage plan any autumn you like, no questions asked.

The other direction is the problem.

Why leaving Advantage means a health exam

Say you're on Medicare Advantage and you want to go back to Original Medicare with a Medigap policy. You can drop the Advantage plan during Annual Enrollment easily enough. But to buy that Medigap policy, in most states, you have to pass medical underwriting.

That means the insurer gets to look at your health history. Depending on what it finds, it can charge you more, impose a waiting period for a pre-existing condition, or turn you down completely. This isn't a loophole. It's the default rule in the majority of states, and it's spelled out plainly on Medicare.gov.

The cruel timing is that the people most desperate to leave an Advantage plan are usually the ones who just got sick, which is exactly when underwriting works against them. Ruth was healthy in 2019 when she could have sailed into any Medigap policy. By 2026, with a cancer diagnosis on her chart, she was the applicant insurers price high or decline. The moment she needed the escape hatch was the moment it locked.

The narrow windows where you can't be turned down

There are exceptions, and knowing them is worth real money.

The cleanest one is the Medigap trial right. If you joined a Medicare Advantage plan as the very first thing you did when you became eligible for Medicare, and within the first 12 months you decide it isn't working, an insurer must sell you a Medigap policy with no medical questions asked. That's a one-time, first-year-only escape. Ruth blew past it years ago without knowing it existed.

There's also a broader set of "guaranteed issue" situations that open a 63-day window with no underwriting: your Advantage plan leaves your area or shuts down, you move out of its service area, or the plan misled you, among a handful of others. Those are protections for when the plan fails you, not for when you simply change your mind.

Outside those windows, in most of the country, you're underwritten. Full stop.

Where your state quietly changes the math

Your ZIP code can flip this entire calculation, so check your own before assuming the national rule applies to you.

Connecticut, Massachusetts, and New York require insurers to sell Medigap year-round regardless of health, which means the one-way door swings both ways there. Maine gives residents a guaranteed-issue month each year. And as of August 1, 2026, Minnesota is adding annual guaranteed-issue protections for people ages 65 to 70. A handful of other states have their own partial rules.

If you live in a guaranteed-issue state, much of the trap in this post doesn't apply to you, and you have more freedom to try Advantage and reverse course later. If you don't, treat the initial decision as close to permanent.

What Advantage actually costs when you're the sick one

The $0 premium is real, and for a healthy retiree who mostly needs checkups, an Advantage plan can be a fine deal. The bill comes due when you get seriously ill.

Every Advantage plan has an out-of-pocket maximum, and for 2026 that cap can run as high as $9,250 for in-network care, with the average in-network limit for PPOs around $6,592, according to KFF. A bad health year can push you to that ceiling. On Original Medicare with a Medigap Plan G, by contrast, you'd typically pay only the annual Part B deductible and then very little on top, which is the whole reason people pay the Medigap premium in the first place.

Then there's the friction. In 2024, Medicare Advantage insurers received about 53 million prior authorization requests and denied roughly 4.1 million of them, close to 8%, KFF found. The striking part: when patients appealed those denials, insurers reversed themselves about 81% of the time, meaning four out of five denied services were medically necessary after all. Most people never appeal. They just go without the care or eat the cost.

New rules that took effect in 2026 force plans to answer urgent authorization requests within 72 hours and standard ones within 7 days, and to publish their denial numbers. That's progress. It doesn't change the underlying deal: an Advantage plan can make you ask permission before it pays.

The 2027 changes worth knowing this fall

Because Annual Enrollment for 2027 coverage runs October 15 to December 7, 2026, a few finalized changes are about to matter.

Part D drug costs are rising. For 2027, the standard Part D deductible climbs to $700, up from $615 in 2026, and the out-of-pocket threshold rises to $2,400 from $2,100, per CMS. If you take expensive medications, run next year's numbers rather than assuming this year's plan still fits.

Those popular supplemental benefit debit cards are getting reined in, too. Starting in 2027, plans must electronically restrict the cards to plan-approved items, verify purchases at checkout in real time, and let any unspent balance expire at year's end. The grocery-card perk that helps sell these plans is becoming narrower and more use-it-or-lose-it.

None of that is a reason to panic. It's a reason to actually read the Annual Notice of Change your plan mails you every September instead of tossing it, because the plan you have in 2026 is not necessarily the plan you'll have in 2027.

How to decide before the door closes behind you

The mistake isn't choosing Medicare Advantage. For plenty of people it's the right call. The mistake is choosing it without knowing the return trip is the hard one.

When you first become eligible for Medicare is the one moment you have maximum freedom, because your initial Medigap enrollment window comes with guaranteed issue and no underwriting. That's the cheapest time to buy Medigap you will ever have. If you lean toward Original Medicare plus Medigap but want to test Advantage first, at least understand you're likely spending your best guaranteed-issue opportunity to do it, unless your state protects you or you use the 12-month trial right on purpose.

If you're already in an Advantage plan and content, you don't need to do anything. But if you have a chronic condition, a diagnosis you're managing, or a strong preference for a specific specialist or hospital, price a Medigap policy now, while you're as healthy as you're going to be, rather than waiting for the year you're forced to move.

Bottom Line

The freedom to switch Medicare plans every fall is real in one direction and sharply limited in the other. Before Annual Enrollment opens on October 15, take these steps:

1. Find out if your state offers guaranteed-issue Medigap. If you're in Connecticut, Massachusetts, New York, Maine, or Minnesota (ages 65 to 70, starting August 1, 2026), the trap mostly doesn't apply and you have more room to change your mind. Everyone else should treat the initial Medigap window as their one clean shot.

2. If you're newly eligible, get a Medigap quote before you commit to Advantage. Your first enrollment is the only time you're guaranteed a policy with no health questions. Know what you're giving up if you skip it.

3. If you're in an Advantage plan and healthy, price Medigap anyway this fall. Underwriting only gets harder as you age and accumulate diagnoses. A quote today tells you whether the escape hatch is still open and what it costs.

4. Read your plan's Annual Notice of Change when it arrives in September. The 2027 Part D deductible ($700) and the new restrictions on benefit cards mean your plan is changing under you, and Annual Enrollment (October 15 to December 7) is your window to respond.