Medigap Open Enrollment: Your 6-Month Guaranteed Issue Right Explained

The Medigap Open Enrollment Period (OEP) is a one-time, 6‑month window that starts the first month you are both age 65 and enrolled in Medicare Part B. During this period, you have guaranteed issue rights — insurers must sell you any Medigap policy they offer, regardless of your health history, and cannot charge you a higher premium because of pre‑existing conditions. This is your single best opportunity to buy a Medigap plan without medical underwriting.

Important: This guaranteed issue window applies only if you are turning 65 and enrolling in Part B for the first time. If you are under 65 and on Medicare due to disability, you generally get a Medigap OEP when you turn 65 (or when you enroll in Part B after disability), not before. And if you are currently in a Medicare Advantage plan, you cannot buy a Medigap policy unless you disenroll from that plan during a permissible period (such as the Medicare Advantage Open Enrollment Period or a Special Enrollment Period). Verify your situation before using the rules below.

When the 6‑Month Clock Starts

The OEP begins on the first day of the month in which you turn 65 and have Part B coverage. If you enroll in Part B at age 65 (during your Initial Enrollment Period), the OEP starts the same day your Part B takes effect. For example, if your 65th birthday is in June 2025 and you are enrolled in Part B beginning June 1, 2025, your Medigap OEP runs from June 1, 2025 through November 30, 2025.

If you delay Part B enrollment because you have group health coverage from an employer, the OEP does not begin until you actually sign up for Part B — even if that is years after age 65. The 6‑month window opens regardless of how late you are, but you only get it once.

Important caveat: The OEP is tied to your Part B effective date, not to the general Medicare enrollment periods (Initial Enrollment Period, General Enrollment Period). If you enroll in Part B during the General Enrollment Period (January 1–March 31) and it becomes effective July 1, your Medigap OEP runs from July 1 through December 31 of that year.

What Guaranteed Issue Rights Allow You to Do

During these 6 months, an insurance company cannot:

• Deny you a policy based on any pre‑existing condition (diabetes, heart disease, cancer history, etc.)
• Charge you a higher premium because of your health status
• Impose a waiting period for pre‑existing conditions (though some states allow a 6‑month waiting period for coverage of pre‑existing conditions not treated in the prior 6 months)

Outside the OEP, insurers can use medical underwriting — they may reject you, exclude conditions, or charge more. This is why the OEP is critical.

Practical implication for your next decision: For most people, the best move is to buy either Plan G or Plan N immediately when the window opens. Do not delay. Even if you are healthy today, medical underwriting later could block you or raise premiums. The peace of mind of a guaranteed‑issue purchase is worth the monthly premium. If you are still deciding, enroll in the plan that best fits your expected future health needs — you cannot easily switch later without underwriting.

Which Medigap Plans Are Available During OEP?

You can buy any Medigap plan letter (A, B, C, D, F, G, K, L, M, N) offered by insurers in your state — with one exception: Plans C and F (and the “High Deductible” version of Plan F) are not available to new Medicare beneficiaries who became eligible after January 1, 2020. If you turned 65 after that date, you cannot buy Plan C or F, even during the OEP. Plan G and Plan N are the most popular alternatives for new enrollees.

In states like Massachusetts, Wisconsin, and Minnesota, the standardized plan letters differ, but the guaranteed issue protections still apply to the plans offered in those states.

Three Expert Tips for Maximizing Your OEP

1. Apply before day 1 of the 6‑month window, not after.

Actionable step: As soon as you receive your Medicare card with your Part B effective date, start comparing Medigap plans. You can sign up as early as the month before your Part B starts, but coverage cannot begin before the OEP opens.
Common mistake: Waiting until the last month of the 6‑month window. If you become seriously ill during month 5, you may still get a policy — but if you wait until month 6 and the insurer processes your application after the window closes, you lose guaranteed issue rights.

2. Compare premiums from multiple insurers for the same plan letter.

Actionable step: Use Medicare.gov’s plan finder or contact several licensed agents to get quotes for Plan G or Plan N in your zip code. Premiums can vary by 50 % or more between companies for identical coverage. For example, Plan G monthly premiums in many states range from $150 to $300 — a $1,800‑per‑year difference.
Common mistake: Assuming all Plan G policies have the same premium. Community‑rated, issue‑age‑rated, and attained‑age‑rated policies charge differently; an issue‑age‑rated policy locks in your rate based on age at purchase and may be cheaper over time.

3. Do not assume you can switch Medigap plans later without underwriting.

Actionable step: Choose the plan that best fits your expected future health needs, not just today’s budget. Most states offer no other guaranteed issue windows for switching (except in very limited circumstances like losing employer coverage or moving out of a plan’s service area).
Common mistake: Buying a plan with a lower monthly premium but higher out‑of‑pocket costs (like Plan K or L) and hoping to upgrade to Plan G later. You will almost certainly face medical underwriting if you try to switch after the OEP ends. Plan K’s out‑of‑pocket maximum in 2025 is $7,060, and Plan L’s is $3,530 — compare that to Plan G, which covers all Part B excess charges and coinsurance after the $257 Part B deductible.

A Realistic Trade‑off: Plan N vs. Plan G

Plan N offers a lower monthly premium (typically $10–$20 less than Plan G) but charges copays of up to $20 for doctor visits and $50 for emergency room visits (waived if admitted). If you visit the doctor 6 times a year, that’s an extra $120 in out‑of‑pocket costs. Over a year, Plan N may be cheaper if you are healthy and rarely visit the doctor. But if you have chronic conditions requiring frequent visits, Plan G’s zero copays can save you money. Choose based on your expected usage, not just the monthly premium. If you are uncertain, pick Plan G for the broadest coverage — switching later is risky.

How to Verify Your Part B Effective Date (Concrete Step)

Before planning your OEP, confirm the exact month your Part B coverage started. Look at your red, white, and blue Medicare card — the date printed under “Part B” is the month your coverage takes effect (e.g., “06‑01‑2025”). If you have a my Social Security account (ssa.gov/myaccount), log in and click “Medicare details” to see the effective date. If you enrolled in Part B during the General Enrollment Period (Jan 1–Mar 31), the effective date is July 1 of that year. Write that date down — it defines your 6‑month window.

Before You Enroll: A Quick Decision Aid

Use these five checks to confirm you are ready to apply during your Medigap OEP. Each item is a pass/fail test.

• [ ] Part B effective date confirmed: You know the exact month your Part B coverage started. (If you are not yet enrolled in Part B, you cannot start the OEP.)
• [ ] You are within the 6‑month window: Your current date is less than 6 months after your Part B effective month. (Count months: effective June 1 → window ends November 30, not December 1.)
• [ ] You have compared premiums for the same plan letter: You have quotes from at least two insurers for Plan G, Plan N, or another plan you are considering.
• [ ] You understand which plans are off‑limits: If you became eligible for Medicare after January 1, 2020, you cannot buy Plan C or Plan F. Ensure you are not wasting time on unavailable options.
• [ ] You are ready to apply before the window closes: You have the application or agent contact ready. Do not wait until the last 15 days — allow time for processing and unexpected issues.

If you pass all five checks, you are in good shape to enroll.

What Happens If You Miss the Window

After your 6‑month OEP ends, you lose guaranteed issue rights. If you try to buy a Medigap policy later:

• Insurers can ask about your health history and may decline you.
• They can impose pre‑existing condition waiting periods.
• Premiums may be significantly higher based on your age and health.
• You may only qualify for “guaranteed issue” under special circumstances: losing employer group health coverage, moving out of a plan’s service area, or your Medicare Advantage plan leaving the market. These events trigger a separate Medigap open enrollment window (usually 63 days) but only apply to specific scenarios.

Concrete example: Maria turned 65 in March 2025 and enrolled in Part B effective March 1, 2025. She did not buy a Medigap policy during her OEP (March–August 2025). In November 2025 she develops a heart condition and applies for Plan G. The insurer sees her medical records, denies her application, and she cannot get any Medigap plan. She now must rely on Original Medicare alone (which has no out‑of‑pocket cap) or switch to a Medicare Advantage plan (which has annual out‑of‑pocket limits). This is a common — and expensive — mistake.

State‑Specific Rules to Know

Three states do not use the same Medigap OEP as the rest of the country:

• Massachusetts: Offers a 12‑month open enrollment from the start of Part B. The same guaranteed issue protections apply, but you have twice as long.
• Wisconsin: Has a unique plan structure. The OEP is 6 months, but the plans letters differ (Basic, Plus, Extended). Guaranteed issue still applies.
• Minnesota: Also uses state‑specific plan types. The OEP rules match federal guidelines, but the plan letters are different.

If you live in any other state, the standard 6‑month federal OEP applies.

Final Takeaway

The 6‑month Medigap Open Enrollment Period is your only chance to buy any Medigap plan without medical questions. Mark your calendar on the first day your Part B becomes effective and act within that window. Premiums and plan availability change yearly — always verify current options at Medicare.gov or call 1‑800‑MEDICARE.

Disclaimer: Medicare rules, premiums, and plan availability change annually. This article is for informational purposes only and does not constitute financial, legal, or medical advice. Consult a licensed insurance agent or Medicare.gov for personalized guidance.