74% of Medicare Advantage Enrollees Could Be Denied Medigap Later. Here’s Why.

One of the most important Medicare decisions happens when you first choose between Medicare Advantage and Original Medicare with a Medigap policy. At 65, both paths may look relatively easy to enter, especially when you are healthy. What many beneficiaries do not realize is that moving between those systems years later may be much more difficult.

New research from KFF found that 74% of Medicare Advantage enrollees in 2023 had at least one pre-existing medical condition that could potentially result in a Medigap denial if they later applied outside a protected enrollment period. That represented about 20.9 million people. The finding does not mean 74% would definitely be denied, but it highlights a major Medicare planning risk that many people do not consider when making their initial decision.

Medicare Advantage and Medigap Work Very Differently

Medicare Advantage and Medigap are not simply two versions of the same insurance. Medicare Advantage replaces the way you receive Original Medicare Part A and Part B benefits through a private insurer, while Medigap works alongside Original Medicare to help cover deductibles, copayments and coinsurance. You cannot use Medigap to pay Medicare Advantage cost sharing.

Medicare Advantage often attracts beneficiaries with low or $0 additional premiums, prescription coverage and benefits such as dental, vision, hearing or fitness programs. In exchange, beneficiaries may have provider networks, prior authorization requirements and cost sharing when medical services are used. Medigap generally requires a separate monthly premium but can provide much more predictable medical expenses when paired with Original Medicare.

Neither system is automatically right for everyone. The problem is assuming that you can freely move from one to the other later if your priorities change.

Your Best Medigap Opportunity May Come Only Once

Federal law gives beneficiaries a six-month Medigap Open Enrollment Period. That period begins when you are 65 or older and enrolled in Medicare Part B. During that window, insurers generally cannot use your health history to deny you a Medigap policy or charge more because of existing medical conditions.

That protection is extremely important. Someone undergoing cancer treatment, living with heart disease or managing other serious health conditions can generally still buy available Medigap coverage during this initial enrollment window. Their health status does not eliminate the federal protection.

Once that six-month period ends, the rules can become very different. Unless you qualify for another guaranteed-issue right or live in a state with additional protections, an insurer may be allowed to evaluate your medical history before deciding whether to issue a policy.

That Is Where the 74% Number Becomes Important

KFF reviewed Medicare Advantage encounter data and compared beneficiaries’ diagnoses with health questions commonly found on Medigap applications. It found that 74% of Medicare Advantage enrollees had at least one condition that could potentially trigger a denial under medical underwriting.

Some of the most common conditions were not rare diseases. About 25% had peripheral vascular disease, 24% had chronic kidney disease, 21% had coronary artery disease and 21% had diabetes with related complications. Those are exactly the kinds of medical issues that become more common as people age.

The percentage also increased significantly among older beneficiaries. KFF found that 88% of Medicare Advantage enrollees age 85 and older had a condition that could potentially trigger a Medigap denial. That means the ability to switch can become more difficult precisely when healthcare needs are becoming more significant.

“Could Be Denied” Is Different From “Trapped for Life”

This distinction matters. A Medicare Advantage beneficiary with a medical condition is not automatically trapped in the plan forever. Someone can leave Medicare Advantage and return to Original Medicare during permitted enrollment periods, but getting a Medigap policy to cover Original Medicare’s cost-sharing gaps is a separate question.

Original Medicare by itself does not have an annual out-of-pocket maximum. Someone who leaves Medicare Advantage but cannot qualify for Medigap could therefore face the 20% Part B coinsurance and other cost sharing that Medigap would otherwise help cover. That financial exposure is one reason access to supplemental coverage matters so much.

There are also federal guaranteed-issue protections and state-specific rules that can allow some beneficiaries to obtain Medigap without underwriting. The 74% statistic should therefore be understood as potential underwriting exposure, not proof that three-quarters of beneficiaries can never change coverage.

The First Year of Medicare Advantage Has a Special Protection

Someone who joins Medicare Advantage when first eligible for Medicare at 65 receives an important federal trial right. If that beneficiary changes their mind within the first 12 months and returns to Original Medicare, they generally have a protected opportunity to purchase a Medigap policy.

That first year can therefore serve as a genuine trial period. Someone who discovers that their doctors are out of network, dislikes prior authorization requirements or simply prefers Original Medicare may be able to reverse the decision without going through normal medical underwriting.

The danger is assuming that the same right continues indefinitely. Once that first-year trial protection expires, returning to Original Medicare may still be possible, but obtaining Medigap can become much less certain.

Dropping Medigap for Medicare Advantage Also Comes With a Trial Right

There is another federal trial right for people who already had Medigap and decide to try Medicare Advantage for the first time. If they return to Original Medicare within the first year, they may generally be able to get their previous Medigap policy back if the insurer still offers it. If the old policy is unavailable, other protected Medigap options may be available.

Again, the 12-month limit matters. Someone who stays in Medicare Advantage for several years may no longer have the same federal guarantee. If health changes during those years, medical underwriting may become the barrier to obtaining Medigap later.

That makes the initial decision more consequential than many beneficiaries realize. Medicare Advantage can be a good long-term choice, but it should not be selected with the assumption that moving into Medigap years later will always be easy.

Health Problems Often Appear After the Decision Is Made

Consider someone who enters Medicare Advantage at 65 because they are healthy, take few medications and rarely see a specialist. They may reasonably decide that paying a substantial Medigap premium every month does not seem worthwhile. Their plan is to keep the inexpensive coverage while healthy and buy Medigap later if medical needs increase.

The flaw is that deteriorating health can be exactly what makes the later Medigap application more difficult. A cancer diagnosis, stroke, serious heart condition or other medical event can occur before the person decides to switch. Outside guaranteed-issue protections, that medical history may then be considered during underwriting.

In other words, waiting until you need more comprehensive supplemental protection can sometimes mean waiting until it is harder to obtain. That is the risk beneficiaries should understand at the beginning.

Medigap Underwriting Is Not Standardized Like Medigap Benefits

Standardized Medigap policies have defined benefit structures, but individual insurers can have different underwriting guidelines when federal or state guaranteed-issue protections do not apply. One company’s application may not evaluate every condition in exactly the same way as another company’s application.

That means a medical condition does not automatically guarantee rejection from every insurer. KFF specifically describes the 74% as beneficiaries with conditions that could result in denial based on questions appearing across the Medigap applications it reviewed.

Other factors can matter as well. KFF notes that recent hospitalizations, home health care, nursing-facility care or pending medical tests may also appear on underwriting applications, meaning the share potentially affected could be even larger than the diagnoses captured in its analysis.

Where You Live Can Completely Change the Rules

Medigap protections are not identical across the country. Federal law creates the basic guaranteed-issue protections, but states can provide additional rights that make switching much easier. That means two retirees with identical health conditions can face very different options simply because they live in different states.

KFF reports that New York, Connecticut and Massachusetts provide continuous Medigap open enrollment protections, while a growing number of states provide annual opportunities to switch policies without traditional medical underwriting. Sixteen states had some form of Medigap “birthday rule” in 2026, allowing existing Medigap policyholders to change coverage around their birthdays under state-specific conditions.

These state laws are especially important before assuming you cannot qualify for coverage. Medicare itself advises beneficiaries to contact their State Insurance Department because state protections may go beyond federal rules.

A Medicare Advantage Plan Leaving Your Area Can Also Create Rights

There are situations where losing Medicare Advantage coverage can generate additional protections. If a Medicare Advantage plan terminates its contract with Medicare or stops serving a beneficiary’s area, special enrollment rules can allow the person to move back to Original Medicare.

Certain qualifying events can also produce Medigap guaranteed-issue rights. The exact policy choices and deadlines depend on the situation, so beneficiaries need to pay close attention to notices from their plan and Medicare. Missing the application window can mean losing the protection.

This is why “once you choose Medicare Advantage, you can never get Medigap” is incorrect. There are multiple exceptions, but they depend on specific circumstances and deadlines rather than a universal right to switch whenever someone wants.

Medigap Has a Different Kind of Long-Term Stability

Once someone successfully purchases a standardized Medigap policy, the policy is generally guaranteed renewable. Medicare says the insurer must renew it each year even if the beneficiary develops health problems, as long as premiums are paid and limited exceptions such as fraud or insurer insolvency do not apply.

That protection helps explain why some beneficiaries are willing to pay higher monthly premiums for Medigap. They are not only purchasing help with today’s copayments and coinsurance. They are also securing supplemental coverage that generally cannot later be taken away simply because their health deteriorates.

The premium itself can increase over time, however. Guaranteed renewable does not mean guaranteed price, and beneficiaries should consider whether rising premiums will remain affordable throughout retirement.

Medicare Advantage Has Its Own Important Protection: An Annual Spending Limit

Medicare Advantage offers a different form of financial protection. Plans must place an annual maximum on what beneficiaries pay out of pocket for covered Part A and Part B services. Original Medicare does not have the same built-in annual cap.

That means Medicare Advantage should not be presented simply as the riskier option. Many beneficiaries value its lower premiums, integrated prescription coverage, additional benefits and annual spending limit. For someone whose preferred doctors are in network, an Advantage plan may work extremely well.

The issue is flexibility. Someone choosing Medicare Advantage should understand that the ability to purchase Medigap later may depend on health, state rules and whether a guaranteed-issue situation applies.

Do Not Choose Medicare Advantage With a Plan to “Switch When I Get Sick”

That is the strategy the new KFF research should make retirees reconsider. Medicare Advantage can be a perfectly reasonable permanent choice, but it is risky to select it solely because you are healthy today while assuming Medigap will remain available whenever health deteriorates.

The timing works against that plan. Medical conditions often become more common with age, while federal Medigap protections become more limited after the initial enrollment and trial-right periods. KFF’s finding that 74% of Medicare Advantage members already had potentially deniable conditions demonstrates just how common that problem can become.

A better approach is to evaluate Medicare Advantage based on whether you would be comfortable remaining in that system if your health changed. Look at the plan’s network, hospitals, specialists, prior authorization requirements and maximum out-of-pocket exposure before enrolling.

And Do Not Choose Medigap Without Considering the Premium

The opposite mistake is assuming everyone should buy Medigap because future switching may be difficult. Medigap premiums can represent thousands of dollars a year and can rise over time. A retiree needs enough room in the budget to maintain the coverage for the long term.

Someone who cannot comfortably afford the premiums may find Medicare Advantage provides more sustainable coverage. Another person may value nationwide provider access and predictable medical expenses enough to justify the added monthly cost.

There is no universal Medicare winner. The decision involves choosing which set of trade-offs fits the beneficiary’s health, finances and preferences.

Ask This Question Before You Turn 65

Instead of asking only which Medicare option costs less today, ask a harder question: Which system would I want if my health were significantly worse five or 10 years from now? That changes the analysis.

If you choose Medicare Advantage, determine whether you would be comfortable staying with that type of coverage over the long term. If you choose Original Medicare with Medigap, decide whether you can reasonably afford the premiums as you age. Neither answer should depend entirely on how healthy you happen to be at 65.

Medicare decisions are unusual because some choices become harder to reverse over time. Understanding that before the first enrollment decision can prevent an unpleasant surprise years later.

The 74% Statistic Is a Warning About Flexibility, Not a Verdict on Medicare Advantage

KFF’s new research does not prove that Medicare Advantage traps 74% of its members for life. It shows that nearly three-quarters of enrollees had health conditions that could create an underwriting obstacle if they later wanted Medigap and did not have guaranteed-issue protection. That is a major distinction, but it does not make the finding any less important.

Medicare Advantage may still be the right choice for millions of people. Medigap may be worth the additional premium for others who value broader provider access and greater predictability. The key is making the initial decision while understanding that moving from one system to the other may not be equally easy in both directions.

Your health at 65 should not be the only factor driving the choice. The better Medicare decision considers the person you may be at 75 or 85, when healthcare needs could look very different and some of today’s options may no longer be guaranteed.