TL;DR
Medicare open enrollment is an annual period for making certain changes to Medicare coverage, while Medigap open enrollment is generally a one-time six-month window tied to being 65 or older and enrolled in Part B. The distinction matters because federal protections against health-based denial or higher premiums for Medigap applications generally apply during that initial window, not each fall.
A Seniors Guide report comparing Medicare open enrollment with Medigap open enrollment highlights a consequential difference: Medicare’s annual period returns each year, but the six-month Medigap window generally occurs only once. The timing can affect whether someone can buy a Medigap policy without health-based underwriting, making it important for people choosing between Original Medicare and Medicare Advantage.
Medicare open enrollment runs from Oct. 15 through Dec. 7 each year, according to the report. During that period, beneficiaries can make certain coverage changes, including switching between Original Medicare and Medicare Advantage and reviewing or changing Medicare Part D prescription drug coverage. The report identifies those dates as the 2026 window.
Medigap open enrollment is a separate six-month period. It begins on the first day of the month in which a person is both at least 65 and enrolled in Medicare Part B, the report says. During that window, a person can buy any Medigap policy sold in their state, and an insurer cannot deny coverage or charge more because of pre-existing health conditions, under the protections described in the report.
Medigap is private supplemental insurance that helps pay some out-of-pocket costs associated with Original Medicare, such as coinsurance, copayments and deductibles. It is not available to people enrolled in Medicare Advantage. People who want prescription drug coverage generally need a separate Part D plan; Medigap policies sold after 2005 do not include that coverage, according to the report.
A One-Time Window for Medigap Protections
The difference between the two calendars can affect both access to coverage and its price. Medicare’s annual fall period gives beneficiaries recurring opportunities to make certain Medicare plan changes, but it does not restart the initial Medigap enrollment protections. Someone who delays applying for Medigap may find that an insurer can review their health history, depending on state law and any applicable guaranteed-issue rights.
That can matter for people who prefer Original Medicare but want help with its cost-sharing. The report says that after the six-month window, insurers in most states may use medical underwriting, potentially denying an application or charging a higher premium based on health. The exact outcome depends on the person’s circumstances and state rules; the annual Medicare enrollment period alone does not guarantee the same Medigap protections.
The choice is also not simply between two enrollment periods. People must first have both Medicare Part A and Part B to purchase Medigap, and they cannot use a Medigap policy to supplement Medicare Advantage. Comparing the coverage, premiums and enrollment rights before choosing a Medicare arrangement can help avoid assuming a later annual enrollment period will reopen every option.
How the Two Enrollment Calendars Work
Medicare’s initial enrollment period is generally a seven-month window: it starts three months before the month a person turns 65, includes their birthday month and continues for three months afterward. The report says people who miss this period may have another opportunity to enroll during Medicare open enrollment, though enrollment timing and penalties can depend on individual circumstances and other coverage.
Medigap’s six-month period has a different trigger: the person must be 65 or older and enrolled in Part B. It does not recur every year. The report notes that people still working may be able to sign up for Medicare while covered by an employer plan, but coordination rules can vary, so individual circumstances matter.
Most states standardize Medigap offerings into plans identified by letters, although Massachusetts, Minnesota and Wisconsin use different standardization systems, according to the report. It cites KFF data indicating that Plan G accounted for 46% of policyholders in 2025; the source says full-year 2026 figures were not yet available. Plan F was reported as the second-most common, at roughly 30% to 36%.
“The Medigap open enrollment period is a six-month window that starts on the first day of the first month you or you and your spouse are both age 65 or older and enrolled in Medicare Part B.”
— Medicare, as summarized in the Seniors Guide report
State Rules and Individual Eligibility
The report gives a general description, not a determination of any individual’s eligibility or guaranteed-issue rights. State laws and personal circumstances can affect whether someone may buy Medigap after the initial window, whether an insurer can use medical underwriting, and what protections apply. The report says applicants in most states may face underwriting after the six-month period, but exceptions and other guaranteed-issue situations are not detailed.
It is also not clear from the report how a specific employer plan interacts with an individual’s Medicare enrollment decision. Medigap premiums and policy availability vary by insurer and location, and the report does not provide price comparisons. Its Plan G market figure is for 2025 policyholders, not a full-year 2026 count.
Check Dates Before Choosing Coverage
People considering a coverage change should verify their own enrollment dates and options with Medicare, their state’s State Health Insurance Assistance Program or a licensed insurance professional. Those considering Medigap should pay particular attention to the month their Part B coverage begins and how that date relates to the six-month window.
The next annual Medicare open enrollment period is scheduled for Oct. 15-Dec. 7, 2026. That period allows certain Medicare coverage changes, but it does not, by itself, restore the initial Medigap enrollment protections. Beneficiaries should confirm current plan terms, costs and state-specific rights before making a decision.
Key Questions
Does Medicare open enrollment happen every year?
Yes. The annual period runs from Oct. 15 through Dec. 7. It allows certain Medicare plan changes, including changes involving Medicare Advantage and Part D coverage.
When does Medigap open enrollment start?
The six-month period generally starts on the first day of the month when you are 65 or older and enrolled in Medicare Part B.
Can I buy Medigap if I have Medicare Advantage?
No. The report says Medigap is available only to people with Original Medicare, meaning Medicare Part A and Part B. Medigap does not supplement Medicare Advantage.
Can an insurer reject a Medigap application after the six-month period?
In most states, insurers may use medical underwriting after the initial window, which can affect acceptance or premiums. State rules and other guaranteed-issue rights may change the result, so check the rules that apply to your situation.
Does Medigap cover prescription drugs?
Medigap policies sold after 2005 do not include prescription drug coverage, according to the report. People seeking that coverage generally need a separate Medicare Part D plan.
Source: seniorsguide.com
