Medigap Open Enrollment Calculator

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

What to do next

1. 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.
2. If your window is open, Review Medicare context 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. Medicare plan networks, drug coverage, and costs can change each year. Before you enroll, check your doctors, prescriptions, pharmacies, and current plan documents. Get quotes from multiple carriers — the benefit is standardized, so premium is the only variable.
3. 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 Sales Agent to confirm what you qualify for.
4. 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

• Medigap fit assessment — decide whether Medigap or Medicare Advantage is the better fit for your needs
• Medicare Advantage vs. Medigap cost — compare total annual costs side by side
• When should I sign up for Medicare — understand your enrollment windows and deadlines
• Initial Enrollment Period — learn about the 7-month window around your 65th birthday