When does my Medigap Open Enrollment Period start?

Your Medigap Open Enrollment Period starts the first month you are both age 65 or older AND enrolled in Medicare Part B. It lasts exactly 6 months. The trigger is your Part B effective date — not your birthday. If you delayed Part B enrollment because you had employer coverage, your OEP starts when your Part B begins, not when you turned 65. Your Part B effective date is printed on your Medicare card.

What happens if I miss my Medigap Open Enrollment Period?

If you miss your Medigap OEP, you lose the guaranteed issue protections. You can still apply for Medigap through medical underwriting, but insurers can ask about your health history and may charge higher premiums, impose waiting periods for pre-existing conditions, or deny coverage altogether. Some states — including New York, Connecticut, Massachusetts, and Maine — have stronger consumer protections that may still allow you to buy Medigap. You may also have a secondary guaranteed issue window if you experience a qualifying event, such as leaving a Medicare Advantage plan within your first 12 months.

Can I buy Medigap during Medicare Advantage Open Enrollment (January–March)?

Switching from Medicare Advantage back to Original Medicare during the January 1–March 31 MA Open Enrollment Period does not automatically grant you Medigap guaranteed issue rights. You can switch to Original Medicare during that window, but to buy Medigap without underwriting, you need either a qualifying guaranteed issue event (such as being within your first 12 months of MA enrollment) or an open Medigap OEP. Otherwise, you'll need to apply through standard medical underwriting.

Medigap Open Enrollment Calculator

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Key takeaway: Your Medigap Open Enrollment Period is a one-time, 6-month window — during this window, no insurer can turn you down, charge you more for your health history, or make you wait for coverage to kick in. Once it passes, those protections are gone.

What this helps you decide

Whether your 6-month guaranteed issue window is currently open, not yet started, or already closed
Whether you need to act immediately to lock in Medigap coverage at standard rates before the window closes
What your options are if your OEP has already passed and you're applying through medical underwriting
Whether you qualify for any other guaranteed issue rights that could give you a second protected window

Who this is for

People who are turning 65 and enrolling in Part B for the first time and want to understand when their Medigap window opens
People who delayed Part B enrollment due to employer coverage and are now newly enrolled — their OEP starts at Part B enrollment, not at age 65
People who are 65 or older, enrolled in Part B, and have never bought a Medigap policy — they need to understand whether their window is open or closed
People currently in Medicare Advantage who are considering switching to Original Medicare + Medigap and want to know if they have any protected access remaining

Example results

Example 1: Person turns 65 in March 2026 and enrolls in Part B effective March 2026. This person's Medigap OEP runs from March 2026 through August 2026 — six months starting the same month they hit both qualifying conditions simultaneously (age 65+ and Part B enrollment). During this entire window, any insurer offering Medigap in their state must sell them any plan at standard rates, regardless of their health history, any pre-existing conditions, or any ongoing treatments. They could have had a heart attack last year, be currently managing diabetes, or be mid-treatment for cancer — none of that matters during OEP. They can compare Plan G ($165.85/month average) and Plan N ($122.98/month average) and buy whichever fits their needs. The window closes August 31, 2026. If they don't act by then, these protections expire.

Example 2: Person turned 65 in 2022, delayed Part B enrollment until April 2026 due to employer coverage. This is an important and often misunderstood case. The Medigap OEP is tied to Part B enrollment, not your 65th birthday. This person was covered by their employer plan until they retired and dropped that coverage, triggering a Special Enrollment Period for Part B. Their Part B effective date is April 2026. That means their Medigap OEP starts April 2026 and runs through September 2026, even though they've been 65 for four years. They have the full six-month guaranteed issue window available to them — same protections as someone who just turned 65. The key document they'll need is proof of their Part B effective date, which appears on their Medicare card.

Example 3: Person is 67, enrolled in Part B at 65, never purchased Medigap. This person's OEP opened in the month they enrolled in Part B at 65 and closed six months later. It has passed. They no longer have guaranteed issue rights under the OEP. To buy a Medigap policy now, they must apply through medical underwriting. That means the insurer can ask about their health history, run it against their underwriting guidelines, and decide whether to offer coverage — and at what price. In many states, insurers can charge more, add waiting periods for pre-existing conditions, or deny coverage altogether. This is not a dead end — many people buy Medigap through underwriting successfully — but the terms are entirely up to the insurer. Some states (including Massachusetts, Minnesota, Connecticut, New York, Maine, and a handful of others) have stronger consumer protections that allow purchase of Medigap with fewer restrictions even outside OEP.

Sample scenarios

Scenario	Input	Result
Turning 65, enrolling in Part B immediately	Part B effective: March 2026, age 65+	OEP: March 2026 – August 2026. Guaranteed issue. Any plan, any insurer, standard rates.
Delayed Part B due to employer coverage	Turned 65 in 2022, Part B effective: April 2026	OEP: April 2026 – September 2026. Full guaranteed issue window starts at Part B enrollment, not birthday.
Missed OEP, healthy, wants Medigap now	Age 67, enrolled in Part B at 65, no Medigap purchased	OEP closed. Must apply through medical underwriting. Approval, pricing, and terms up to insurer. State protections may apply.
Leaving MA within first 12 months	Enrolled in MA at 65, wants to return to Original Medicare within year 1	Qualifies for guaranteed issue rights for specific Medigap plans (Plans A, B, C, D, F, G, K, L). Act before the 12-month window closes.

What to do next

Confirm your Part B effective date — that's the date that controls everything. Your Medigap OEP starts the month you are both 65 or older and enrolled in Part B. Your Part B effective date is printed on your Medicare card (the red-white-and-blue card) under "Part B (Medical)." If you enrolled in Part B before turning 65 due to disability, the OEP rules are different — your window typically starts at 65 in that case. If you're not sure of your effective date, call 1-800-MEDICARE or log into Medicare.gov.
If your window is open, compare plans now — don't wait. The guaranteed issue window doesn't give you advance warning when it's about to close. If you're in month 4 or 5 of your OEP, the clock is running. Plan G covers everything except the $283 Part B deductible. Plan N covers the same with copays up to $20 for office visits and $50 for ER visits, and it does not cover Part B excess charges. Get quotes from multiple carriers — the benefit is standardized, so premium is the only variable.
If your window has passed, check whether you have any other guaranteed issue rights. Specific life events can trigger a second protected period: leaving an MA plan within 12 months of enrollment, losing other creditable coverage involuntarily, your plan leaving Medicare, or moving out of a plan's service area. If any of these apply, you have a 63-day window to buy certain Medigap plans without underwriting. Contact 1-800-MEDICARE or a licensed agent to confirm what you qualify for.
If you live in a state with extra protections, research your state's rules. States including New York, Connecticut, Massachusetts, Maine, and a few others require insurers to offer Medigap on a guaranteed issue basis year-round or provide additional open enrollment windows. If you've missed your federal OEP, your state may still give you options. Your State Health Insurance Assistance Program (SHIP) offers free, unbiased guidance — find your local SHIP at shiphelp.org.

Key facts

The Medigap Open Enrollment Period is a one-time, 6-month window that begins the month you are both age 65 or older and enrolled in Medicare Part B. It does not repeat, and there is no way to re-open it under standard federal rules.
During your Medigap OEP, insurance companies cannot deny coverage, charge higher premiums, or impose waiting periods for pre-existing conditions. This protection applies to all standardized Medigap plans available in your state.
If you miss your Medigap OEP, you may still have guaranteed issue rights in specific situations — such as leaving a Medicare Advantage plan within the first 12 months of enrollment, or losing other coverage involuntarily. These secondary windows are 63 days and typically cover specific plans only.

Related decisions

Decision area	Tool	What it answers
Enrollment	Initial Enrollment Period Calculator	When your 7-month Medicare eligibility window begins and ends based on your 65th birthday
Enrollment	When Should I Sign Up for Medicare?	The best time to enroll based on your work status, other coverage, and age
Enrollment	Special Enrollment Period Checker	Whether a life event qualifies you for enrollment outside the standard windows
Enrollment	Late Enrollment Penalty Checker	How much extra you'll pay monthly if you missed your enrollment window
Enrollment	Part B Penalty Calculator	The exact 10%-per-year premium increase for delayed Part B enrollment
Enrollment	Part D Penalty Calculator	The 1%-per-month premium increase for gaps in creditable drug coverage
Costs	Cost Scenario Planner	Estimated annual spending across plan types at different health utilization levels
Costs	Advantage vs. Medigap Cost Comparison	True cost difference between Medicare Advantage and Original Medicare with Medigap
Costs	IRMAA Calculator	Whether your income triggers higher Part B and Part D premiums
Costs	Part A Premium Estimator	Your monthly Part A premium based on work history and quarters of coverage
Costs	M3P Calculator	How the Medicare Prescription Payment Plan smooths your drug costs into monthly payments
Coverage	Doctor & Drug Assessment	Whether your providers and prescriptions are covered by a specific plan
Coverage	Part D Shopping Tool	Which Part D plan has the lowest total annual cost for your specific medications
Coverage	Travel & Network Risk Assessment	How your coverage works outside your home area and which plan types travel best
Employer/COBRA	COBRA vs. Medicare	Why COBRA can trigger permanent Medicare penalties and how costs compare
Employer/COBRA	Employer Coverage vs. Medicare	Whether your employer plan or Medicare is primary and when to transition
Employer/COBRA	HSA & Medicare Compatibility	How Medicare enrollment affects HSA eligibility and what to do before enrolling
Planning	Caregiver Readiness Checklist	Whether you have everything in place to help a loved one with Medicare decisions
Planning	Document Gatherer	Which documents you need to have ready before enrolling or changing plans
Planning	Medigap Fit Assessment	Whether Medigap or Medicare Advantage is the better fit for how you use healthcare
Planning	Medigap Open Enrollment Window	Whether you're inside your one-time guaranteed issue window for Medigap
Planning	Medicare Savings Program Eligibility	Whether your income qualifies you for help paying Medicare premiums and cost-sharing