Updated August 3, 2026. Quick answer: you get one six-month window, it starts the first month you have Part B and are 65 or older, and it never comes back. Inside it an insurer must sell you any policy it offers regardless of your health. Outside it, in most states, it may ask about your health and say no.
What the window is
One-time, 6 months. Starts the first month you have Medicare Part B AND are 65 or older. If Part B is delayed by active employer coverage, it starts when Part B actually begins. It does not repeat.
Note the second condition. If you delayed Part B because you were still working with employer coverage, the window starts when Part B actually begins — not on your 65th birthday. How working past 65 changes the timing.
What it guarantees
“During it, an insurance company can’t refuse to sell you any of the medical policies it offers. They also can’t use medical underwriting to decide whether to accept your application or deny you coverage due to pre-existing health problems.”
And on price: “Insurance companies can’t charge you more because of pre-existing health problems.”
So inside the window your health is irrelevant to whether you can buy and what you pay. That is the entire value of it, and it is unusual — very little else in individual insurance works that way.
What changes when it closes
“Outside your Medigap Open Enrollment Period: You may have to pay more for a policy. Fewer policy options may be available to you. The insurance company is allowed to deny you a policy if you don’t meet their medical underwriting requirements.”
Three separate things, and they compound: you may pay more, fewer policies may be available to you, and you can be declined outright. A person in good health at 65 who assumes they can buy later is making a bet on their health at an unknown future date, which is precisely the bet insurers price.
The exceptions that exist afterwards
Federal law does provide guaranteed-issue rights in specific situations — mostly when coverage you already had ends through no fault of your own — plus two trial rights. The full list and the deadlines.
Some states add their own rights on top. Whether yours does is worth knowing before you decide, not after.
What this means in practice
The six-month window is the moment the coverage decision is cheapest to get wrong and easiest to get right, because it is the one time the door is open in both directions. If you are inside it now and unsure, the question is not which product is better — it is which choice leaves you with more options later. The asymmetry.
General information drawn from Medicare, CMS and state insurance-department publications, not insurance advice. Medicare rules, plan availability and dollar figures change every year, and state rules differ. Every figure here is year-labelled and every source is named so you can check it against your own situation. We do not sell insurance and receive nothing if you buy a plan.