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September 15, 2026 · 8 min read

Six months. That is the entire window in which Texas law guarantees you can buy any Medicare Supplement plan regardless of your health. Here is when it starts, what it protects, and the mistakes that cost people the protection.

Written by Amiel Garcia · Professional Insurance Solutions

The short answer

Your Medigap Open Enrollment Period is a single six-month window that begins the month you are both 65 or older and enrolled in Medicare Part B. Inside it, federal law guarantees you the right to buy any Medicare Supplement policy sold in your state, at that carrier’s best available rate, regardless of your health history. A carrier cannot decline you, and cannot charge you more, for a pre-existing condition.

Outside that window, none of those protections automatically apply. Carriers can generally medically underwrite a Medigap application — ask health questions, decline you, or charge a higher premium — unless you separately qualify for one of a small number of other guaranteed-issue situations. This is the single fact that should drive the timing of the whole decision.

When the window actually starts

The trigger is Part B, not your birthday alone. Your six months begin the first month you are 65 or older and enrolled in Medicare Part B — which for most people lines up with turning 65, but not for everyone.

Retiring at or before 65 — Part B typically starts the month you turn 65, so the Medigap window opens then too, six months from that first day of Part B coverage.
Still working past 65 with employer coverage — if you delay Part B because a current employer’s group plan covers you, your Medigap window does not open until you actually enroll in Part B, which could be well after 65. Enrolling in Part B early "just in case" can accidentally start a clock you did not mean to start.
Already 65 and enrolling in Part B late — the window still runs from whenever Part B actually begins, not from your 65th birthday. Someone who enrolls in Part B at 68 gets their six-month Medigap window starting then, not four years earlier.

It does not reopen every year

This is the most expensive misconception in Medicare, and it is not close. Medicare Advantage has an annual re-enrollment period every October through December. Medigap does not work that way — the guaranteed-issue window described here happens once, tied to your first Part B enrollment, and then it is gone.

People who assume it renews annually often discover the truth only when they try to switch plans years later and get medically underwritten for the first time — sometimes declined outright for a condition that would not have mattered a decade earlier, inside the window.

What happens if you miss it

Missing the window does not mean you cannot get a Medigap policy — carriers in Texas will still generally accept applications outside it. It means the carrier can ask health questions and can decline the application or price it higher based on the answers. Some conditions that would have been completely irrelevant inside the guaranteed-issue window can mean a decline outside it.

A small number of other situations create their own separate guaranteed-issue rights outside the main window — most commonly losing a Medicare Advantage plan the carrier discontinued, or moving out of that plan’s service area. These are narrower and time-limited in their own right, and they are worth a specific conversation rather than an assumption that one applies.

Getting the timing right

Start the conversation about three months before your 65th birthday, not after it.
If you plan to keep working past 65 on employer coverage, confirm with HR whether that coverage is considered "creditable" before deciding when to take Part B.
If you are already past 65 and never took Part B, your window has not started yet — it opens whenever Part B does.
Do not let a Medicare Advantage plan’s annual renewal period lull you into thinking Medigap has the same yearly opportunity. It does not.

Approaching 65 or already past your Medigap window?

Tell us your birthday and your Part B effective date and we will tell you, plainly, where you stand — inside the window with guaranteed issue, or outside it and needing a different strategy. There is never a fee for the conversation. We place group benefits and Medicare coverage across twelve carriers.

Talk to a Medicare advisor(361) 462-4125

Common questions

The follow-ups we field most often after this conversation.

It starts the first month you are 65 or older and enrolled in Medicare Part B, and it lasts six months. If Part B starts the month you turn 65, the window runs from your 65th birthday month. If you delay Part B — commonly because you are still covered by an employer group plan — the window does not open until whenever Part B actually begins, even if that is well after 65.

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