Medicare Supplement Open Enrollment: Dates, Rules & Deadlines

What Is the Medigap Open Enrollment Period?

The Medicare Supplement Open Enrollment Period (OEP) is a federally protected, one-time, 6-month window that begins on the first day of the month in which you are both age 65 or older and enrolled in Medicare Part B. During this period, insurance companies are legally required to sell you any Medigap plan they offer, with no health questionnaires, no medical exams, and no risk of denial.

This is not the same as the annual Medicare Open Enrollment (Oct 15 to Dec 7), which covers Medicare Advantage and Part D changes. The Medigap open enrollment starts the first month you have Medicare Part B and you're 65 or older, lasts for six months, and is a one-time enrollment period that doesn't repeat every year like the annual Medicare Open Enrollment Period.

Example: If your 65th birthday is in September 2026 and you enroll in Part B starting September 1, 2026, your Medigap OEP runs from September 1, 2026 through February 28, 2027.

With the 2026 standard Part B premium set at $202.90 per month (an increase of $17.90, or just under 10 percent, from the 2025 premium of $185.00) and the annual Part B deductible now $283, up $26 from $257 in 2025, the cost of waiting too long to coordinate Medigap coverage with Part B can be significant. Learn more about enrolling in Medicare for the first time to align your Part B start date with your Medigap OEP.

Guaranteed Issue Rights: What They Mean for You

Guaranteed issue is the cornerstone protection of the Medigap OEP. During this time, an insurance company can't refuse to sell you any of the medical policies it offers, they can't use medical underwriting to decide whether to accept your application or deny you coverage due to pre-existing health problems, they can't charge you more because of pre-existing health problems, and they can't make you wait, except for coverage related to a pre-existing condition.

This applies to Medigap Plans A, B, C, D, F, G, K, and L (availability varies by state). Plan F and Plan C are only available to those who became eligible for Medicare before January 1, 2020. If you didn't have creditable coverage in the 6 months before enrolling, insurers may impose up to a 6-month waiting period for pre-existing conditions, even during your OEP.

Special Guaranteed Issue Rights (Outside the OEP)

Even after your Medigap OEP ends, certain life events can trigger temporary guaranteed issue rights, giving you a 63-day window to enroll without underwriting. Common qualifying situations include:

For people newly eligible for Medicare on or after January 1, 2020, guaranteed issue typically covers Plans A, B, D, G, high-deductible G, K, or L (Plans C and F are no longer available to new enrollees). This protection is especially relevant in 2026 given the wave of MA plan terminations. Johns Hopkins projected that 1 in 10 Medicare Advantage enrollees would face forced disenrollment in 2026, and beneficiaries who have had their coverage terminated by their Medicare Advantage insurer have a special guaranteed issue period to purchase a Medigap policy to supplement their coverage under traditional Medicare, meaning they cannot be denied coverage or charged a higher premium for a Medigap policy due to pre-existing conditions. Your GI window typically opens 60 days before your MA coverage ends and extends 63 days after.

What Happens If You Miss the Medigap Open Enrollment Period?

Missing your 6-month window doesn't permanently lock you out of Medigap, but it significantly changes the rules. In most cases, you won't have a right under federal law to switch Medigap policies unless you're within your 6-month Medigap open enrollment period, or you're eligible under a specific situation or guaranteed issue right. Outside the OEP (and without a qualifying guaranteed issue event), insurers in most states can:

• Deny your application entirely based on health status
• Charge higher premiums due to age or pre-existing conditions
• Exclude coverage for certain conditions for a set period

Delayed enrollment is one of the leading reasons many Medicare beneficiaries find themselves unable to qualify for a Medigap policy later on. For a deep dive into what to expect, see our guide on Medigap underwriting after leaving Medicare Advantage.

State-Level Exceptions: Birthday Rules, Anniversary Rules & Year-Round Enrollment

While federal law governs the 6-month Medigap OEP, many states have enacted additional protections that can give you ongoing opportunities to shop or switch plans, even after your OEP has closed. As of 2026, roughly half the states offer Medigap guaranteed issue rights that go above and beyond what the federal government requires. Learn more in our breakdown of Medicare Supplement plans by state.

States with Year-Round or Continuous Guaranteed Issue

A small group of states offers year-round or continuous Medigap protections, meaning you can apply for or switch plans well outside the federal 6-month window:

• New York offers true year-round guaranteed issue for all Medicare-eligible residents
• Connecticut also offers true year-round guaranteed issue
• Vermont offers continuous guaranteed issue for residents 65 and older
• Maine allows continuous switching to a plan with the same or lesser benefits, plus one designated month each year when Plan A is guaranteed issue
• Massachusetts has its own standardized Medigap system with an annual open enrollment window each February and March
• Minnesota (new for 2026) introduces a one-time guaranteed-issue window for ages 65 to 70, effective August 1, 2026

Minnesota House Bill 4, effective August 1, 2026, creates a new guaranteed issue situation that allows individuals aged 65 to 70 who want to enroll in a Medicare supplement policy outside of their initial open enrollment period to enroll during the Medicare annual open enrollment period without medical underwriting or preexisting condition limitations, and the individual may only make this choice once during ages 65 to 70. However, the law also allows a penalty that starts at 15% above the standard community rate for those who enroll during open enrollment of 2026, increases 5% per year, and reaches a maximum penalty of 35% for open enrollment 2029 and beyond, applying for the duration of the policy.

If you live in one of these states, the urgency of the initial OEP is lower, though enrolling early still often secures the lowest rates.

The Birthday Rule: A Second Chance Every Year

Many states now offer a "birthday rule," an annual window (typically 30 to 63 days) around your birthday during which you can switch to an equal or lesser Medigap plan without underwriting. As of 2026, 15 states have active birthday rules, including new additions Delaware and Indiana (effective January 1, 2026) and West Virginia (with policies subject to the rule for policies effective or renewed starting June 1, 2026):

Important: Birthday rules allow you to switch to equal or lesser plans, not upgrade to a plan with richer benefits. You typically cannot move from Plan G to Plan F using a birthday rule. Missouri uses an anniversary rule (60 days around the Medigap policy anniversary, same plan only), not a birthday rule. New Mexico's birthday rule was enacted in 2026 but takes effect January 2027.

Don't Confuse These Two Enrollment Periods

One of the most common Medicare mistakes is confusing the annual Medicare Open Enrollment Period (Oct 15 to Dec 7) with the Medigap OEP. Here's the key distinction:

The October 15 to December 7 window is for Medicare Advantage and Part D changes. It has no impact on Medigap enrollment rules or guaranteed issue protections in most states. There is also a separate Medicare Advantage Open Enrollment Period (Jan 1 to Mar 31) that lets MA enrollees switch plans or return to Original Medicare. Your Medigap OEP is entirely separate and based on your own enrollment timeline.

Turning-65 Enrollment Checklist

Use this timeline to stay on track when you're approaching Medicare eligibility:

For a deeper look at which plans offer the most value and what they cost, explore our 2026 Medicare Supplement cost guide or see how Plan G coverage and costs stack up for new enrollees.

Frequently Asked Questions

When exactly does my Medigap Open Enrollment Period start?

Your Medigap OEP begins on the first day of the month in which you are both age 65 or older and enrolled in Medicare Part B. If you delayed Part B enrollment due to employer coverage, your OEP starts when your Part B coverage begins, not when you turned 65. The window lasts exactly six months from that start date and cannot be extended or repeated.

Can I be denied Medigap coverage if I have pre-existing conditions?

During your Medigap OEP or a qualifying guaranteed issue event, no, because insurers cannot deny you or charge you more due to pre-existing conditions. However, if you didn't have at least 6 months of continuous creditable coverage beforehand, an insurer may impose up to a 6-month waiting period before covering pre-existing conditions. Outside of these protected windows, most states allow medical underwriting, which means an insurer can deny your application or charge significantly higher premiums.

What is the birthday rule and which states have it in 2026?

The birthday rule is a state-level protection that gives you an annual window, typically 30 to 63 days around your birthday, to switch to an equal or lesser Medigap plan without medical underwriting. As of 2026, 15 states have birthday rules: California, Oregon, Idaho, Nevada, Maryland, Louisiana, Illinois, Kentucky, Virginia, Oklahoma, Wyoming, Utah, Delaware, Indiana, and West Virginia. Each state has different window lengths and rules about which carriers and plan types qualify, and New Mexico is set to join this list in January 2027.

Is there any way to get Medigap after missing my open enrollment period?

Yes, but it is more difficult. Outside your OEP, you may still qualify through guaranteed issue rights triggered by specific events such as losing employer coverage, your Medicare Advantage plan leaving your area, or exercising a trial right within your first 12 months on MA. You also have the option to apply with medical underwriting at any time, but there is no guarantee of acceptance. Residents of New York, Connecticut, and Vermont have year-round guaranteed issue protections, while Maine, Massachusetts, and Minnesota offer broader state-specific protections than the federal rule.

Does the annual Medicare Open Enrollment Period (Oct 15 to Dec 7) affect my Medigap plan?

No. The October 15 to December 7 annual Open Enrollment Period is strictly for Medicare Advantage and Part D plan changes. It has no effect on Medigap (Medicare Supplement) plans in most states. Your Medigap OEP is a separate, one-time window tied to your Part B enrollment date, and these two periods are completely independent of each other (except in Minnesota starting August 2026, where ages 65 to 70 get a one-time guaranteed-issue Medigap window during the federal fall enrollment period).