Medicare open enrollment has a Medigap trap most people miss

You have spent years in a Medicare Advantage plan that promised broader benefits and lower premiums than original Medicare coverage.

Now something has changed, whether your plan exited the market, your doctor left the network, or you simply want more flexibility. So you start the process to switch back to original Medicare during the open enrollment window that runs through March 31.

You expect a smooth transition because the right to switch plans during this period is guaranteed under federal Medicare enrollment rules.

But a hidden obstacle on the other side of that switch catches thousands of retirees off guard every single year during this period.

The problem is not about Medicare itself, or even about enrollment deadlines that you might accidentally miss during the process. The real risk involves a separate type of insurance that most people assume they can buy whenever they want, but actually cannot.

Switching to original Medicare without Medigap is a costly gamble

If you leave Medicare Advantage for original Medicare, you will almost certainly want a Medigap policy to help cover deductibles, copays, and coinsurance. Without that supplemental coverage, original Medicare places no annual cap on your out-of-pocket spending, according to the Centers for Medicare and Medicaid Services.

Medigap insurers can refuse to sell you a policy if your medical history or current health conditions make you too expensive to insure. This process is called medical underwriting, and it applies in most states once your initial six-month Medigap enrollment window closes.

Medicare Advantage plans are exiting markets at an unprecedented rate

Roughly 2.9 million Medicare Advantage enrollees had to find new coverage for 2026 after their plans stopped operating in their areas. That figure represents about one in 10 MA enrollees nationwide, according to a study published in February in JAMA.

The average forced disenrollment rate stayed around one percent from 2018 through 2024 before jumping to nearly seven percent in 2025.

“We saw some Medicare Advantage plans that just left the market completely and stopped issuing plans,” said Emily Whicheloe, education director at the Medicare Rights Center.

You may have strong reasons to leave your Medicare Advantage plan behind. Medicare Advantage plans typically offer lower monthly premiums and extra benefits, including vision, hearing, and dental coverage for enrolled members.

Related: AARP warns Medicare costs are outpacing Social Security again

But those plans also require you to use smaller provider networks, and some impose extensive prior authorization rules that can delay care. As insurer profits have sagged, a growing number of MA plans have pulled out of regions they previously served across the country.

Rural counties and areas with lower MA penetration are the most likely to see large-scale plan exits, Johns Hopkins Bloomberg School of Public Health found. More than 54 percent of all Medicare beneficiaries were enrolled in Medicare Advantage plans as of 2025, according to KFF data.

Federal law gives you one guaranteed window to buy Medigap coverage

When you first enroll in Medicare Part B at age 65, federal law provides a six-month open enrollment period specifically for Medigap.

During that window, insurers must sell you any available Medigap plan without reviewing your health history or increasing your premium.

Once that six-month window closes, your guaranteed right to buy Medigap without medical underwriting largely disappears in most states.

Specific situations where you can still get Medigap without underwriting

Not every door closes after that initial enrollment period, and understanding the exceptions could protect you from a devastating coverage gap.

Key guaranteed-issue situations for Medigap coverage:

• Trial right: If you joined Medicare Advantage when first eligible at age 65, you can switch back to original Medicare within your first year.
• Plan exit: If your MA plan leaves your market area, you can purchase Medigap 60 days before or up to 63 days after coverage ends.
• Relocation: If you permanently move outside your MA plan’s service area, the same 60-day-before to 63-day-after enrollment window applies to you.
• Year-round states: Connecticut, Massachusetts, and New York allow you to sign up for Medigap at any point during the year without medical underwriting.
• Maine exception: Maine offers a one-month annual window when insurers must sell Medigap Plan A to all applicants without medical underwriting requirements.

Bonnie Burns, a training and policy consultant at California Health Advocates who specializes in Medicare, noted that the relocation window typically begins when you notify your plan of a permanent move.

Medigap underwriting has gotten significantly tougher in recent years

About 90 percent of Medicare Advantage enrollees aged 65 and older, or roughly 22.4 million people, face medical underwriting for Medigap. They could be denied coverage based on health status alone outside of specific guaranteed-issue windows, KFF reports.

Medigap insurers have been spending more on medical claims as a share of premiums, which has squeezed their profit margins considerably.

Common health conditions that could trigger a Medigap application denial

A KFF review of 15 Medigap applications from 12 major insurers found a long list of conditions and procedures that trigger coverage denial or premium increases for applicants.

Conditions commonly leading to Medigap denial:

• Alzheimer’s disease and other dementias that require ongoing treatment, along with asthma that requires the use of prescription inhalers daily
• Cancer diagnoses, including active treatment, remission status, and certain types of prior cancer history appearing in your medical records
• Congestive heart failure, which affects roughly 12 percent of Medicare beneficiaries and remains a frequent underwriting red flag for applicants
• Diabetes with complications like neuropathy, a condition affecting more than 26 percent of all Medicare beneficiaries across the country today
• End-stage renal disease, high blood pressure, stroke history, prior organ transplants, and pacemaker implants, which are also commonly flagged by insurers

About two-thirds of Medicare beneficiaries have hypertension, and roughly 19 percent have chronic kidney disease, according to KFF data.

Your prescription drug history may now decide your Medigap eligibility

Medigap insurers increasingly require applicants to authorize a prescription drug background check before making any final coverage decisions.

Nick Ortner, a principal and consulting actuary at Milliman and a Society of Actuaries fellow, explained this growing trend among insurers.

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Ortner said that prescription drug history is now often the primary driver of underwriting decisions, rather than physical exams or medical record reviews.

Even if you answer every question on a health questionnaire correctly, your medication records could reveal conditions that trigger a denial.

Free SHIP counselors can help you navigate the Medigap enrollment process

The State Health Insurance Assistance Program, known as SHIP, offers free and unbiased counseling to help you understand your Medigap options within your state.

SHIP counselors can identify which insurers in your area accept applicants with specific diagnoses and which have different waiting periods.

Related: Your Medigap plan could be costing you more than you realize

Ryan Ramsey, associate director of health coverage and benefits at the National Council on Aging, noted that SHIP counselors have access to a Medigap comparison tool beyond what Medicare.gov offers to consumers.

That comparison tool can give you a reliable estimate of what you will pay for Medigap plans based on your age, location, and health.

Steps you should take right now before the March 31 enrollment deadline

You still have a narrow window to make smart decisions about your Medicare coverage, but you need to act before this deadline passes.

Your pre-switch action plan:

• Check Medigap eligibility first: Contact Medigap insurers in your state before you drop your Medicare Advantage plan so you can confirm approval in advance.
• Reach out to your local SHIP: Visit shiphelp.org or call 877-839-2675 to get free, personalized counseling on your Medigap options before you make any switch.
• Review your health history carefully: If you have chronic conditions, understand that underwriting denial is a real and growing possibility in most states across the country.
• Know your state’s specific rules: Thirty-five states offer some guaranteed-issue protections beyond federal minimums for qualifying events, so check what applies to you.
• Never drop your MA plan first: Confirm that you can secure Medigap coverage before finalizing any switch to avoid landing in original Medicare with no supplement.

If you cannot secure Medigap coverage at a reasonable price, staying in a Medicare Advantage plan may actually be your safest option. The March 31 deadline will arrive quickly, and the decisions you make now will shape your health care costs for the entire year ahead.

Related: Saving on Medicare Advantage by Comparison Shopping

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