When Is the Medigap Open Enrollment Period? (2026)

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 an insurer can screen your health instead. That window opens once you're 65 and enrolled in Part B, and it doesn't come back around. 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.1 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 prerequisite sits underneath all of this: Medigap is built for Original Medicare, so generally you need to have signed up for both Part A and Part B before you can buy a policy.1 If you're in a Medicare Advantage plan, that's the thing to sort out first, because Medigap is not designed to pair with it.

Two details in that sentence decide whether you actually get the window you think you have, and CMS spells both out. The first is that "attaining age 65" is not your birthday. CMS says the period never begins on your actual birthday: Social Security and CMS treat you as attaining age 65 on the first day of the month your 65th birthday falls in, and if your birthday is the first of a month, on the first day of the preceding month. So a July 1 birthday means a window that opened June 1.1

The second is that you don't have to wait for the window to open to apply. Section 1882(s)(2)(A) protects an application submitted prior to or during the six-month period, and CMS says that if you apply early enough, you can ask to have the policy start on the first day of your Part B entitlement. That's how you avoid a gap between Part B beginning and Medigap coverage beginning.1

And if you came onto Medicare before 65 through a disability or ESRD, this window is still ahead of you, not behind you. CMS states that such a beneficiary is reclassified as an aged beneficiary on attaining age 65, and because they are already entitled to Part B, their Medigap Open Enrollment Period begins on that date. Years already spent on Medicare do not use it up.1

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.1 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, the statute says the issuer may not deny or condition the issuance or effectiveness of the policy, or discriminate in the pricing of it, because of health status, claims experience, receipt of health care, or medical condition.1 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.2 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.2 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, this particular guarantee goes with it. What replaces it is not a flat no, though, and the difference matters if you are reading this at 68 rather than 65: separate federal guaranteed-issue rights attach in defined circumstances, and some states add their own.1

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."1

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. Don't plan your coverage around catching one of those exceptions, because none of them is guaranteed to happen to you. But if one does happen, it is a real right with a short deadline attached, so check it the week it happens rather than assuming the door shut at 65 and a half. 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.1 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.

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.