The short answer
When you first enroll in Medicare Part B at 65 or older, a one-time, six-month Medigap open enrollment window opens. During those six months, you can buy any Medicare Supplement plan sold in your area with no medical underwriting — the insurer can't turn you down or charge you more because of your health. It's the single most important piece of timing in the whole Medigap world.
Once that window closes, buying or switching Medigap usually means answering health questions, and an insurer can decline you or raise your rate based on your health. That's why missing this window can quietly cost you for the rest of your life.
When the window opens — and why timing matters
Your six-month Medigap open enrollment period starts the first month you have Part B and are 65 or older. It's tied to your Part B start date, and it doesn't reset or come around again. There's no annual Medigap open enrollment the way there is for Medicare Advantage and Part D — this is your one guaranteed shot at any plan with no health questions.
That's why people who delay Part B while working need to think ahead: your Medigap window opens when Part B begins, so if you'll want a supplement, you want to be ready to choose one then. Our overview of Medicare Supplement plans covers how the standardized plans compare.
What to do with your window
The practical move is to use the window deliberately rather than let it pass by default. Compare the standardized Medigap plans, decide whether a supplement fits your situation better than Medicare Advantage, and if it does, enroll while you have guaranteed acceptance. Locking in during the window protects you even if your health changes later.
If you're not sure whether Medigap or Medicare Advantage fits you, that's exactly the decision to make before the window closes — because the two paths get harder to switch between afterward. Our side-by-side plan comparison lays out the tradeoffs.
Frequently Asked Questions
When does the Medigap open enrollment window start?
It starts the first month you're 65 or older and enrolled in Part B, and it lasts six months. It's a one-time window tied to your Part B start date.
What happens if I miss my Medigap window?
After it closes, buying or switching Medigap usually requires medical underwriting, meaning an insurer can decline you or charge more based on your health.
Is there an annual Medigap open enrollment?
No. Unlike Medicare Advantage and Part D, Medigap has no annual open enrollment. Your six-month window at Part B enrollment is your one guaranteed-issue opportunity.
Can I still get Medigap after the window with health problems?
Sometimes, but you may face underwriting and could be declined or charged more, unless you qualify for a separate guaranteed-issue right due to a specific situation.
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