People with Medicare can choose to receive their Medicare benefits through either traditional Medicare or Medicare Advantage, and this choice poses tradeoffs. In traditional Medicare, beneficiaries may see any doctor or hospital that accepts Medicare, generally without needing a referral or prior authorization. However, traditional Medicare includes relatively high cost sharing and there is no cap on out-of-pocket spending, potentially exposing beneficiaries to very high costs. Most people who enroll in traditional Medicare have an additional source of coverage to help with these costs, including employer coverage, Medicaid, or Medigap. Alternatively, in Medicare Advantage, beneficiaries have an out-of-pocket cap and often reduced cost sharing, but may face more limited provider networks and greater use of prior authorization. Beneficiaries may prefer to switch between sources of coverage as their medical needs and financial circumstances change over time.
Medigap, which is supplemental insurance sold by private companies, is the most common source of supplemental coverage for people in traditional Medicare. Medigap helps cover Medicare Part A and B cost-sharing requirements, including deductibles, copayments, and coinsurance, with monthly premiums averaging $244 in 2025 among current Medigap policyholders. Federal law provides a one-time, six-month Medigap open enrollment period when beneficiaries age 65 and older first enroll in Part B, during which insurers cannot deny someone a policy or charge them higher premiums due to their to medical history. Additionally, some states provide additional guaranteed issue opportunities for beneficiaries to purchase Medigap without regard to their pre-existing medical conditions.
However, outside of this initial enrollment period and other specified circumstances, including a 12-month Medicare Advantage trial period for new enrollees, Medigap insurers are allowed to use medical underwriting when issuing Medigap policies and can charge higher premiums or deny coverage to applicants with pre-existing conditions. These limitations can make it more costly or even impossible for Medicare Advantage enrollees with pre-existing conditions to switch to traditional Medicare and buy a Medigap policy, constraining Medicare beneficiaries’ coverage choices.
This analysis examines the share of Medicare Advantage enrollees who have a pre-existing condition that could result in a Medigap denial if they seek to switch to traditional Medicare outside their one-time 12-month trial period, including national estimates and estimates by age and by state. The pre-existing conditions included in the analysis are based on a KFF review of Medigap applications, which list conditions subject to medical underwriting. The analysis uses Medicare Advantage encounter data for all Medicare Advantage enrollees, including those in individual plans available for general enrollment, employer plans, and special needs plans. This analysis includes dual-eligible individuals, who do not require Medigap as long as they have Medicaid coverage but would potentially be subject to underwriting for Medigap if they lose their Medicaid eligibility. This analysis also includes Medicare Advantage enrollees under age 65, who do not have federal guaranteed issue rights to purchase Medigap, but can take advantage of the initial Medigap open enrollment period when they turn 65.
Takeaways
Nearly three-quarters of Medicare Advantage enrollees (74%) or 20.9 million people in 2023 had a pre-existing medical condition identified from KFF’s review of Medigap applications that could result in a denial for a Medigap policy.
At least one in five Medicare Advantage enrollees have a diagnosis for peripheral vascular disease (25%), chronic kidney disease (24%), coronary artery disease (21%), or diabetes with related complications (21%) documented in the Medicare Advantage encounter data, all of which could trigger a Medigap denial.
The share of Medicare Advantage enrollees who have a deniable pre-existing condition rises with age among people 65 and older, with close to 9 in 10 enrollees 85 and older (88%) having a medical condition that could trigger a Medigap denial.
The share of Medicare Advantage enrollees who have a pre-existing condition that could trigger a denial for Medigap varies by state, from a high of 82% in Florida to a low of 59% in Alaska.