Traditional Medicare places no annual limit on what a beneficiary can be required to pay out of pocket. Part A and Part B cost sharing continues without a cap, which for a beneficiary using a routine amount of care over the course of a year is a manageable feature of the program. For someone who receives a serious diagnosis such as cancer, the same feature can instead mean open-ended financial exposure arriving at precisely the moment when the capacity to absorb additional cost is lowest.
Medigap policies exist to close that gap, covering much of the cost sharing that traditional Medicare leaves to the beneficiary. For those who remain in traditional Medicare rather than enrolling in a Medicare Advantage plan, supplemental coverage is the principal mechanism available for limiting financial risk. What is less widely understood is that the right to purchase such a policy is time-limited, and that once the initial window has closed, what a beneficiary is entitled to depends largely on the state in which they live.
The enrollment window, and what follows it
Federal law guarantees a six-month Medigap open enrollment period beginning when a beneficiary is 65 and enrolled in Part B. During that period insurers must issue a policy to any applicant regardless of health status and may not vary the premium on that basis. Once the window closes, most states permit insurers to apply medical underwriting to Medigap applications, which means that an insurer may ask about health history and may decline to issue a policy or charge more on the basis of the answers. Federal law preserves a limited set of guaranteed-issue circumstances, roughly seven situations involving mostly the involuntary loss of other coverage, but these are narrow and a new diagnosis is not among them.
The structural consequence follows from how any voluntary insurance market with underwriting operates, which is that the protection is most readily available to people who do not yet need it and hardest to obtain for those who have recently learned that they do.
How much states diverge
Roughly half of states have adopted protections that go beyond the federal floor, and the differences among them are not minor. Connecticut, Massachusetts, and New York require insurers to issue Medigap policies to beneficiaries aged 65 and older at any point during the year, while Maine provides a one-month guaranteed-issue period annually that is limited to Plan A. As of mid-2026, fifteen states have adopted some form of birthday rule, among them California, Illinois, Louisiana, Maryland, Nevada, Oregon, and Virginia. These rules allow beneficiaries a window around their birthday during which they may switch policies without underwriting, typically to a plan with equal or lesser benefits. Outside of these regimes, a beneficiary who is past the initial enrollment window is generally subject to underwriting.
The result is that two beneficiaries with the same diagnosis, the same income, and the same underlying Medicare coverage can face substantially different financial exposure depending only on the state in which their policy would be issued. This is somewhat unusual, since Medicare is otherwise among the more uniform social programs in the United States, and the variation here arises from state insurance regulation rather than from federal program design.
Why the variation matters
The practical consequences of this patchwork are not especially well documented. Most beneficiaries encounter these rules only at the point when they actually need supplemental coverage, and by then the options available to them were largely determined by decisions their state legislature made years earlier. How much that matters for the people affected, and which groups it affects most, is a question the existing evidence base addresses less thoroughly than the stakes would appear to warrant.