Medigap Enrollment Periods and Eligibility: Guaranteed Issue Rights

The main window to buy a Medigap policy is a one-time, six-month Medigap Open Enrollment Period that begins the first day of the month you are both 65 or older and enrolled in Medicare Part B.¹ Inside that window, insurers must sell you any plan they offer in your state, cannot reject you for health reasons, and cannot charge you more because of pre-existing conditions. Miss it, and in most states you face medical underwriting, higher premiums, or outright denial. A handful of other Medigap enrollment periods exist for specific life events, and some states add their own annual switching windows.

The Six-Month Open Enrollment Period

This is the window that matters most. Federal law gives you one Medigap Open Enrollment Period that lasts six months and starts the first day of the month you are 65 or older and enrolled in Part B.¹ During those six months, insurers cannot use medical underwriting to decide whether to accept you, and they cannot charge more because of existing health conditions.²

The clock runs from your Part B effective date, not from the day you applied for Part B or the day your Medicare card arrived. If Part B starts June 1, your window runs June 1 through November 30. Once those six months expire, federal law does not give you another open enrollment period. Knowing your exact Part B start date is the single most important piece of information.

You need both Part A and Part B before any insurer will sell you a Medigap policy, and you must keep paying your Part B premium to keep the Medigap coverage in force.³⁴ The 2026 standard Part B premium is $202.90 per month, with higher-income beneficiaries paying more.⁵ Drop Part B, and the Medigap policy goes with it.

If You Delayed Part B Because of Employer Coverage

A common misconception: people who delay Part B while working often assume they missed their Medigap window. They didn’t. The six months begins when Part B actually starts, even if that’s years after you turned 65.⁶ The requirement is that you be 65 or older when Part B kicks in.

Pre-Existing Conditions During Open Enrollment

Even inside the open enrollment window, an insurer can impose a waiting period of up to six months for conditions you were diagnosed with or treated for in the six months before your policy’s effective date.² All other covered services are paid normally during that time.

Prior creditable coverage shortens the wait. Each month of previous coverage (employer insurance, COBRA, another Medigap policy, or similar) cancels one month of the waiting period, and six or more months eliminates it entirely.² The credit only applies if you had no gap longer than 63 days.

What Happens If You Miss the Window

Once the six months end and no guaranteed issue right applies, insurers in most states can run medical underwriting on your application. They can deny you outright, charge significantly more because of your health, or impose a full six-month pre-existing condition waiting period.⁶

This is where people get burned. Someone healthy at 65 who skips Medigap, then develops a serious condition at 70, may find no insurer will sell them a policy at any price. There is no federal mechanism to reopen the window just because your health changed. Insurers at this stage still cannot ask about family medical history or require genetic testing, but questions about your personal history, current medications, and recent treatments are standard.⁷

Guaranteed Issue Rights

Certain life events open protected windows where insurers must sell you a Medigap policy no matter your health, cannot charge extra for pre-existing conditions, and cannot impose waiting periods. These guaranteed issue rights typically last 63 days from the end of your prior coverage, so moving quickly matters.

Common triggering events include:⁷

Your Medicare Advantage plan leaves Medicare or stops serving your area, and you switch back to Original Medicare. You can buy Medigap Plans A, B, C, D, F, G, K, or L (Plans C and F only if you were eligible for Medicare before 2020).
You move out of your Medicare Advantage plan’s service area and return to Original Medicare. Same rights as above.
Your employer, retiree, COBRA, or union coverage ends. You can buy Plans A, B, C, D, F, or G, subject to the same 2020 restriction on C and F.
Your Medigap insurer goes bankrupt or your coverage ends through no fault of your own. You can buy Plans A, B, C, D, F, or G.
Your Medicare SELECT plan’s service area no longer covers where you live. You can switch to a different Medigap plan.
An insurer or Medicare Advantage plan misled you or broke the rules. You can buy certain Medigap plans depending on the circumstances.

The 63-day deadline runs from the latest of three dates: when coverage actually ends, when you receive a termination notice, or when a claim denial reveals coverage ended. Keep termination letters and notices as proof you qualify.

Trial Rights for Medicare Advantage Switchers

Two trial-right scenarios come up constantly. If you joined a Medicare Advantage plan when you first became eligible for Part A at 65 and decide within the first 12 months to return to Original Medicare, you can buy any Medigap plan sold in your state with guaranteed issue protections.³

If you dropped an existing Medigap policy to try Medicare Advantage for the first time and want to switch back within 12 months, you can get your old Medigap policy back if the same insurer still sells it. This is a one-time right, not a mechanism for bouncing repeatedly between systems.⁷

COBRA Timing

If you have COBRA that supplements Original Medicare, you can buy a Medigap policy right away or wait until COBRA runs out and use your guaranteed issue right then.⁷ Waiting can make sense when COBRA is generous, but the 63-day clock starts the day COBRA ends.

If You Are Under 65 on Medicare

Federal law does not require insurers to sell Medigap policies to Medicare beneficiaries under 65 who qualify through disability or End-Stage Renal Disease.¹ This is a real gap. Depending on where you live, you may not be able to buy any Medigap policy until you turn 65.

Most states have added their own rules. Some require insurers to offer at least one Medigap plan to disabled beneficiaries under 65; others make all plans available on a guaranteed issue basis, though under-65 premiums are often substantially higher. Contact your State Insurance Department to see what applies where you live. When an under-65 beneficiary later turns 65, they get a fresh six-month open enrollment period with the full federal protections, regardless of how long they’ve already been on Medicare.

State Birthday and Anniversary Rules

About 15 states have annual enrollment windows, often called birthday rules, that let existing Medigap policyholders switch to a different plan around their birthday without medical underwriting. The details vary. Some states give you 30 days around your birthday; others give 60 or 63. Most limit switches to a plan with equal or lesser benefits, so you can move from Plan G to Plan N but not the other direction. A few restrict switches to your current insurer or its affiliates rather than letting you shop across companies.

These state windows are separate from the federal open enrollment period and from guaranteed issue rights. They exist for people who already have a Medigap policy and want to change it, usually for a lower premium with a different company. If you live in one of these states, your birthday becomes an annual prompt to compare prices.

Two Boundaries Worth Knowing Before You Apply

You cannot buy a Medigap policy while enrolled in a Medicare Advantage Plan. The two are separate paths through Medicare, and to buy Medigap you must either stay on Original Medicare or disenroll from Advantage first.³

If you became newly eligible for Medicare on or after January 1, 2020, you cannot buy Plan C or Plan F at all, in any enrollment window. Those plans covered the Part B deductible, and the Medicare Access and CHIP Reauthorization Act of 2015 closed them to new enrollees.⁷ For most new beneficiaries, Plan G or Plan N is the closest substitute. Every lettered plan is standardized, so a Plan G from one insurer covers exactly what a Plan G from another insurer covers, and your choice comes down to price and service rather than benefits.

1
Medicare. Get Ready to Buy
2
Office of the Law Revision Counsel. 42 US Code 1395ss – Certification of Medicare Supplemental Health Insurance Policies
3
Medicare. Learn How Medigap Works
4
Medicare.gov. Medicare Costs
5
Centers for Medicare & Medicaid Services. 2026 Medicare Parts A and B Premiums and Deductibles
6
Medicare.gov. When Can I Buy a Medigap Policy
7
Medicare.gov. Choosing a Medigap Policy