Buy a Medigap policy during your one-time, six-month open enrollment window and no insurer can turn you down; buy it a day late and your health is fair game again. That window opens once you're 65 and enrolled in Part B, and it never reopens. Below is exactly when yours starts, what the guarantee protects, and why waiting is the costliest mistake people make with Medigap.
In This Guide
- Key Takeaways
- When Is the Medigap Open Enrollment Period?
- What the Guarantee Actually Protects
- What Happens Once the Six Months End
- When Your Medigap Open Enrollment Period Starts, and How Not to Miss It
- Frequently Asked Questions
- Learn More
When Is the Medigap Open Enrollment Period?
Here's the direct answer. Your Medigap Open Enrollment Period is a one-time, six-month window, and it starts on the first day of the first month in which you're both 65 or older and enrolled in Medicare Part B.Centers for Medicare & Medicaid Services. (n.d.). Get Medigap Basics. medicare.gov. Retrieved Jul 17, 2026, from https://www.medicare.gov/health-drug-plans/medigap/basics That's straight from Medicare: the window "starts the first month you have Medicare Part B and you're 65 or older."
Notice that it's two conditions, not one, and the later of the two is what matters. If you take Part B the month you turn 65, both boxes get checked at once and your window opens then. If you're 66 but only just now signing up for Part B, your window opens now, not last year. And Medigap, the Medicare Supplement Insurance sold by private carriers to fill in Medicare's gaps, is what you're shopping for during that stretch.
One thing worth clearing up: this is not the fall Open Enrollment you hear ads about every October. That annual window is for switching Medicare Advantage and Part D drug plans. Your Medigap Open Enrollment Period is its own separate, once-in-a-lifetime thing, and it doesn't reopen every year.Centers for Medicare & Medicaid Services. (n.d.). Get Medigap Basics. medicare.gov. Retrieved Jul 17, 2026, from https://www.medicare.gov/health-drug-plans/medigap/basics Miss it, and it's gone.
What the Guarantee Actually Protects
This window matters because of what comes attached to it: a guaranteed right to buy. During those six months, any insurance company has to sell you any Medigap policy it offers in your state, and it can't hold your health against you.
Specifically, an insurer can't deny you a policy, can't put you through medical underwriting, and can't charge you more because of your health status, a pre-existing condition, your claims history, or a current medical condition.Centers for Medicare & Medicaid Services. (n.d.). Get Medigap Basics. medicare.gov. Retrieved Jul 17, 2026, from https://www.medicare.gov/health-drug-plans/medigap/basics Medical underwriting is the health screening insurers otherwise use to decide whether to cover you and at what price. Medicare.gov puts it plainly: during this time, "the insurance company can't deny you coverage due to pre-existing health problems."
So the smart play is to shop while that protection is live. You've got diabetes, a heart condition, a cancer history? None of it can be used to reject your application or raise your premium. That's the one stretch of your life when your medical record can't be held against your application.
There is one limit here that people miss, and it's worth understanding before you assume the coverage starts clean. Getting the policy is protected. Having it pay from day one is not. During open enrollment, an insurer may still refuse to cover your out-of-pocket costs for a pre-existing condition for up to six months. It can't impose that waiting period if you had at least six months of continuous creditable coverage (an employer or retiree plan, Medicare Advantage, and similar) before you enrolled.Centers for Medicare & Medicaid Services. (2025). Choosing a Medigap Policy: A Guide to Health Insurance for People with Medicare (CMS/NAIC, 2025) - Medicare.gov. medicare.gov. Retrieved Aug 8, 2026, from https://www.medicare.gov/publications/02110-choosing-a-medigap-policy.pdf This is the one way open enrollment falls short of a true guaranteed issue right, the kind you get from a Medicare Advantage trial right or from losing other coverage, under which the insurer must cover all your pre-existing conditions with no waiting period at all.Centers for Medicare & Medicaid Services. (2025). Choosing a Medigap Policy: A Guide to Health Insurance for People with Medicare (CMS/NAIC, 2025) - Medicare.gov. medicare.gov. Retrieved Aug 8, 2026, from https://www.medicare.gov/publications/02110-choosing-a-medigap-policy.pdf If you're coming straight off employer coverage, ask the carrier to confirm in writing that your prior coverage waives the wait.
Your state may layer on extra Medigap protections beyond this federal floor, so it's worth a quick check with your state insurance department. But the six-month open enrollment window is the nationwide baseline, and it's the one you can count on everywhere.
What Happens Once the Six Months End
Once your window closes, the guarantee goes with it. There's no federal rule saying an insurer has to sell you a Medigap policy anymore.Centers for Medicare & Medicaid Services. (n.d.). Get Medigap Basics. medicare.gov. Retrieved Jul 17, 2026, from https://www.medicare.gov/health-drug-plans/medigap/basics
In practice that means an insurer can put you through medical underwriting. It can look at your health, decide you're too expensive to cover, and turn you down. Or it can offer you a policy but charge you more for it. Medicare.gov says it about as bluntly as a government site ever says anything: "After this period, you may not be able to buy a Medigap policy, or it may cost more."Centers for Medicare & Medicaid Services. (n.d.). Get Medigap Basics. medicare.gov. Retrieved Jul 17, 2026, from https://www.medicare.gov/health-drug-plans/medigap/basics
That's what makes this a buy-now-or-maybe-never decision. When you're 65 and healthy, it's tempting to skip the extra premium and figure you'll add a Medigap policy later, once you actually need it. The trouble is that "once you actually need it" is exactly when your health can be used to price you out or shut you out. The people most likely to get denied later are the ones who waited because they felt fine.
There are limited situations down the road that can give you a guaranteed-issue right, and some states are more generous than the federal minimum. But none of that is a promise, and you shouldn't plan your coverage around catching one of those exceptions. The dependable protection is the six-month window in front of you.
When Your Medigap Open Enrollment Period Starts, and How Not to Miss It
Because the window is tied to your Part B start date, protecting it really comes down to knowing when your Part B coverage begins.Centers for Medicare & Medicaid Services. (n.d.). Get Medigap Basics. medicare.gov. Retrieved Jul 17, 2026, from https://www.medicare.gov/health-drug-plans/medigap/basics The month it starts, if you're already 65, your Medigap clock starts ticking too.
A few situations catch people off guard:
- Turning 65, taking Part B on time. Your window opens the month your Part B does. Start comparing Medigap plans a month or two ahead so you can buy early in the window, not scrambling at the end of it.
- Still working past 65 with real employer coverage. If you delay Part B because you have active group coverage through your job (or your spouse's), your Medigap window doesn't start until your Part B does. It waits for you. The risk is losing track of it once you finally retire and enroll.
- Already 65, just now enrolling in Part B. Good news here: your six months start now, from this Part B enrollment, not back when you hit 65.
If you're not sure when your Part B kicks in, that date is on your Medicare card and in your account at Medicare.gov. Pin it down, count six months forward, and treat that as your deadline to have a Medigap policy in hand if you want one.
Frequently Asked Questions
How long is the Medigap Open Enrollment Period?
Six months. It's a one-time window that starts the first month you're both 65 or older and enrolled in Medicare Part B, and it doesn't repeat. Once those six months are up, the guaranteed right to buy is gone.
Can I be denied a Medigap policy after my open enrollment period ends?
Yes. After the window closes, there's no federal guarantee that an insurer will sell you a policy. It can put you through medical underwriting, review your health, and either turn you down or charge you more. That's the main reason not to wait.
Is the Medigap Open Enrollment Period the same as Medicare's fall Open Enrollment?
No, and they're easy to mix up. The fall window (October 15 to December 7) is for changing Medicare Advantage and Part D drug plans, and it comes every year.Centers for Medicare & Medicaid Services. (n.d.). Open Enrollment. medicare.gov. Retrieved Aug 8, 2026, from https://www.medicare.gov/health-drug-plans/open-enrollment Your Medigap Open Enrollment Period is separate, tied to your own Part B start date, and happens only once.
What if I'm still working at 65 and delaying Part B?
Your Medigap window waits for your Part B. It doesn't start until you're both 65 or older and actually enrolled in Part B, so delaying Part B with active employer coverage delays the window too. Just don't lose track of it when you retire and sign up.
Do I have to answer health questions during my Medigap Open Enrollment Period?
No. Inside the window an insurer can't use medical underwriting, deny you, or charge you more based on your health, pre-existing conditions, or claims history. That protection is exactly what makes buying during the window so valuable. One thing it can still do is hold off covering your out-of-pocket costs for a pre-existing condition for up to six months, and even that is off the table if you had at least six months of continuous creditable coverage right before the policy started.Centers for Medicare & Medicaid Services. (2025). Choosing a Medigap Policy: A Guide to Health Insurance for People with Medicare (CMS/NAIC, 2025) - Medicare.gov. medicare.gov. Retrieved Aug 8, 2026, from https://www.medicare.gov/publications/02110-choosing-a-medigap-policy.pdf
Learn More
Find personalized help timing your Medigap Open Enrollment Period at brevy.com.
The information on Brevy.com is for educational purposes only and is not a substitute for professional legal, financial, or medical advice. Rules vary by state and program and change frequently. Always verify with the relevant agency or a qualified professional. Brevy is not a law firm, financial advisor, or healthcare provider.