The 6-month Medigap open enrollment period is a one-time window during which insurance companies must sell you any Medigap (Medicare Supplement) policy they offer, regardless of your health. It begins the first day of the month you turn 65 and are enrolled in Medicare Part B, and it lasts exactly six months. Once it closes, getting a Medigap policy becomes significantly harder and more expensive.
When the Window Opens
Two conditions must be true for your 6-month window to start: you must be 65 or older, and you must be enrolled in Medicare Part B. For most people, both happen at the same time, so the clock starts the month they turn 65. But if you delay Part B enrollment because you’re still covered through an employer, your Medigap open enrollment period doesn’t start until the month your Part B coverage actually begins, even if that’s years after your 65th birthday.
This matters because the window is tied to Part B, not to your birthday or to Part A. If you retire at 68 and sign up for Part B at that point, your six months begin then.
What Protections You Get During This Period
During these six months, federal law gives you three major protections that disappear once the window closes:
- No medical underwriting. Insurers cannot ask health questions, review your medical history, or deny you coverage based on pre-existing conditions. Any Medigap plan sold in your state is available to you.
- No premium surcharges for health problems. Companies cannot charge you more because of current or past medical conditions. You pay the same rate as any other enrollee your age.
- Immediate coverage. Your policy starts right away, with one exception: insurers can impose a waiting period of up to six months before covering costs related to a pre-existing condition you were treated for before enrolling. If you had prior health coverage (called “creditable coverage”) without a gap, that waiting period is typically shortened or eliminated.
The Pre-Existing Condition Waiting Period
Even during your open enrollment window, insurers can delay covering expenses tied to conditions you were already being treated for. Under federal law, this waiting period maxes out at six months from the start of your policy. So if you had knee replacement surgery three months before your Medigap coverage began, the insurer could refuse to pay Medigap benefits for follow-up care on that knee for up to six months.
The key detail: if you carried continuous health insurance coverage before enrolling (employer insurance, marketplace coverage, or another plan without a significant gap), insurers must credit that time against the waiting period. Someone who transitions directly from employer coverage to Medicare with no gap will generally have pre-existing conditions covered from day one.
What Happens If You Miss It
After the six months expire, Medigap insurers in most states can use medical underwriting. This means they can ask detailed questions about your health, review your medical records, and make decisions based on what they find. The consequences are real:
- Denial of coverage. An insurer can refuse to sell you a policy entirely based on conditions like diabetes, heart disease, or cancer history.
- Higher premiums. Even if approved, you may be charged significantly more than someone who enrolled during their open enrollment period.
- Exclusions on pre-existing conditions. Insurers may agree to cover you but exclude costs related to specific health problems.
There is no federal right to a second open enrollment period. This is a one-time protection, which is why insurance advisors consistently call it the single most important enrollment window in Medicare.
If You’re Under 65
Federal law only guarantees the 6-month Medigap open enrollment period for people who are 65 or older. If you qualify for Medicare before 65 due to a disability or end-stage renal disease, federal law does not require insurers to sell you a Medigap policy on guaranteed terms. However, many states have stepped in to fill this gap with their own protections, requiring insurers to offer Medigap policies to under-65 Medicare beneficiaries during an initial enrollment window. The specifics vary by state, so your options depend on where you live.
States That Offer Broader Protections
Four states go well beyond the federal minimum. Connecticut, Massachusetts, Maine, and New York require Medigap insurers to offer policies either continuously throughout the year or during an annual enrollment period to Medicare beneficiaries age 65 and older, without regard to medical conditions. If you live in one of these states, missing the federal six-month window is far less consequential because you can apply later without medical underwriting.
Several other states have expanded protections in more limited ways, such as offering guaranteed issue rights after specific qualifying events or extending open enrollment protections to beneficiaries under 65 with disabilities. Your state insurance department can tell you exactly what applies where you live.
Trial Rights After Medicare Advantage
There is one notable exception to the “one-time window” rule. If you drop a Medigap policy to join a Medicare Advantage plan for the first time, you get a 12-month trial right. If you decide Medicare Advantage isn’t working for you within that first year, you can return to Original Medicare and get your old Medigap policy back (if the same company still sells it) without going through medical underwriting.
Similarly, if you joined a Medicare Advantage plan when you first became eligible for Part A at 65, you can switch to Original Medicare and buy certain Medigap policies within the first year without medical underwriting. These trial rights exist specifically to let people test Medicare Advantage without permanently losing access to Medigap coverage.
Outside of these trial rights and the protections offered by certain states, the six-month open enrollment period is your only guaranteed opportunity to buy any Medigap plan at standard rates. If you’re approaching 65 or about to start Part B, shopping for Medigap during this window is worth prioritizing, even if you’re healthy now and don’t think you’ll be denied coverage later.