Medigap and Preexisting Conditions: What Medicare Beneficiaries Must Know

If you have a preexisting condition — diabetes, heart disease, COPD, a history of cancer, or even something as common as sleep apnea — buying a Medigap policy outside of a protected enrollment window can be surprisingly difficult, and in many states, legally impossible to guarantee. Unlike Medicare Advantage plans, which must accept all Medicare beneficiaries regardless of health status during open enrollment, Medigap policies sold outside of specific guaranteed issue windows are subject to medical underwriting in most of the country. That means the insurance company can review your health history, ask detailed questions about your diagnoses and medications, and either deny your application outright or charge you a higher premium based on what they find.

The single most important protection available to Medicare beneficiaries is the Medigap Open Enrollment Period. This is a one-time, six-month window that begins the first month you are both 65 or older and enrolled in Medicare Part B. During this window, federal law prohibits Medigap insurers from denying you a policy, charging you more than a healthy applicant, or imposing a waiting period for most preexisting conditions — with one narrow exception. If you have had a gap in creditable coverage in the six months before applying, an insurer may impose up to a six-month waiting period before covering that specific preexisting condition, though they still must sell you the policy. Once this six-month window closes, it does not reopen under federal rules, and the protections disappear unless a separate qualifying event applies.

What counts as a preexisting condition for Medigap underwriting purposes is broader than many people expect. Insurers in states that allow medical underwriting typically look back at conditions diagnosed or treated in the past two to ten years, depending on the state and the insurer. Common conditions that can trigger a denial or surcharge include Type 2 diabetes, atrial fibrillation, chronic kidney disease, obesity, Alzheimer's disease, multiple sclerosis, and even a history of tobacco use. Some insurers will decline applicants who are currently receiving treatment for cancer, regardless of prognosis. In 2025, the average Medigap Plan G premium for a 65-year-old non-smoker in good health runs roughly $120 to $180 per month depending on the state and insurer — but applicants with significant health histories who are accepted may face premiums 20 to 50 percent higher in states that permit it, or simply receive a denial letter.

There are federally guaranteed issue rights outside of the initial open enrollment period, but they are narrow and tied to specific life events. If your Medicare Advantage plan leaves your service area or loses its Medicare contract, you have a guaranteed right to purchase certain Medigap plans — specifically Plans A, B, C, F, K, or L — without medical underwriting. The same right applies if you drop a Medigap policy to try a Medicare Advantage plan for the first time and then want to return within 12 months — this is sometimes called a "trial right." If your employer-sponsored retiree coverage ends, that can also trigger a guaranteed issue right. These windows are typically 63 days from the triggering event, so acting quickly matters. Missing the deadline by even a few weeks means losing the protection entirely.

Thirteen states have enacted additional consumer protections that go beyond federal minimums, and if you live in one of them, your options are meaningfully better. California, Idaho, Illinois, Kentucky, Louisiana, Maine, Maryland, Missouri, Nevada, New Jersey, New York, Oklahoma, and Oregon all have some form of birthday rule or continuous guaranteed issue rights. The birthday rule, as it applies in states like California and Oregon, gives you a 30-day window each year around your birthday to switch to a Medigap plan with equal or lesser benefits without medical underwriting — even if you have significant health conditions. New York and Connecticut go further, requiring insurers to sell any Medigap plan to any Medicare beneficiary year-round, regardless of health status. If you live in one of these states, you have far more flexibility to shop for better rates or switch plans as your needs change. If you live in a state like Florida, Texas, or Pennsylvania, you do not have these protections outside of the federal guaranteed issue windows.

One of the most expensive mistakes beneficiaries make is delaying Medigap enrollment because they feel healthy and want to save money on premiums in the short term. The logic seems reasonable — why pay $150 a month for supplemental coverage when you rarely see a doctor? But Medicare's cost-sharing structure can be brutal for people who develop serious illness without a supplement. In 2025, Medicare Part A carries a $1,676 inpatient hospital deductible per benefit period, with no cap on how many benefit periods you can have in a year. Part B has a $257 annual deductible and then requires 20 percent coinsurance on all covered services — with no out-of-pocket maximum under Original Medicare alone. A single hospitalization followed by outpatient chemotherapy or cardiac rehabilitation could easily generate $10,000 to $30,000 in cost-sharing that a Medigap Plan G would have covered almost entirely. By the time someone realizes they need the coverage, they may no longer be able to get it at a standard rate — or at all.

If you are approaching 65 and have preexisting conditions, the strategic move is to enroll in Medicare Part B as soon as you are eligible and begin your Medigap Open Enrollment Period immediately. Do not delay Part B enrollment to save on premiums if you are within a few months of 65 — the cost of losing your guaranteed issue window almost always outweighs the short-term savings. If you are already past 65 and missed your open enrollment window, check whether you qualify for a federal guaranteed issue right based on a recent life event, and contact your state insurance commissioner's office to find out whether your state offers birthday rule protections or other expanded rights. The National Association of Insurance Commissioners maintains a directory of state insurance departments at naic.org, and Medicare.gov's plan finder tool at medicare.gov/find-a-plan can help you compare available Medigap policies in your ZIP code.

For beneficiaries who are denied Medigap coverage due to health history and do not qualify for any guaranteed issue right, Medicare Advantage may be the only realistic path to capping out-of-pocket costs — since Advantage plans must accept all Medicare beneficiaries during the Annual Enrollment Period from October 15 through December 7 each year, and during the Open Enrollment Period from January 1 through March 31. Medicare Advantage plans in 2025 carry maximum out-of-pocket limits of up to $9,350 for in-network services, which provides some financial protection, though the network restrictions and prior authorization requirements are very different from what Medigap offers. Understanding which path makes sense for your health situation, your finances, and your state's rules is not a one-size-fits-all decision — but knowing the preexisting condition rules before your enrollment window closes is the single most important step you can take.