Medigap open enrollment starts the first month you are both 65 or older and enrolled in Medicare Part B. It lasts 6 months.
That 6-month window is usually the easiest time to buy a Medicare Supplement plan because insurers generally cannot deny you coverage or charge you more because of health problems during that period.
If you only remember one rule, remember this: Part B starts the clock.
What Is Medigap Open Enrollment?
Medigap open enrollment is your one-time federal window to buy a Medicare Supplement policy with the strongest protections.
Medicare says that during this period, an insurance company generally cannot:
- deny you a Medigap policy because of your health
- charge you more because of past or current health problems
- make you wait for coverage because of pre-existing conditions in most cases when you meet prior creditable coverage rules
This is why people who want the freedom of Original Medicare plus a supplement should pay close attention to timing, not just premium.
What Starts the 6-Month Medigap Window?
Two things must be true:
- you are 65 or older
- you are enrolled in Medicare Part B
The window begins on the first day of the month when both are true.
Medicare explains the rule here: When can I buy a Medigap policy?
Simple Examples
These examples are where most of the confusion clears up.
Example 1: You take Part B at 65
If you turn 65 in September and your Part B starts September 1, your Medigap open enrollment window runs:
- September 1 through the end of February
Example 2: You delay Part B because you keep working
If you keep employer coverage past 65 and delay Part B until you retire at 67, your Medigap open enrollment window does not start at 65.
It starts when your Part B actually begins at 67.
If you are sorting through that question now, read Do You Need Medicare at 65 If You’re Still Working? and How to Apply for Medicare Part B After Employer Coverage Ends.
Example 3: You start with Medicare Advantage
If you enroll in Medicare Advantage instead of buying Medigap when Part B starts, your Medigap open enrollment window is still tied to that first Part B effective date.
That matters because many people assume they can try Advantage for a few years and then move to Medigap later with no issue. Sometimes they can. Often they run into underwriting.
This article covers that part in more detail: Can You Switch From Medicare Advantage to Medigap Later?
Why This Window Matters So Much
Missing the Medigap window does not mean you can never buy a supplement.
It means the insurance company may be allowed to ask health questions later and decide whether to accept your application.
In plain English, after your open enrollment window ends, you may face:
- medical underwriting
- higher premiums in some situations
- a denied application
- fewer realistic choices if your health changes
Medicare makes that point directly on its Medigap pages, and I see the real-world version of it when someone waits until after a new diagnosis, surgery, or chronic condition shows up.
If you want the underwriting issue explained clearly, start here: Can You Be Denied a Medicare Supplement Plan?
Is Medigap Open Enrollment the Same as Guaranteed Issue?
No.
People mix these up all the time.
Medigap open enrollment is your 6-month window tied to being 65 or older and starting Part B.
Guaranteed issue rights are special protections that can happen in certain situations outside that window, like losing other qualifying coverage or using a Medicare Advantage trial right.
Those rights are real, but they are narrower than full open enrollment and they depend on the facts of your case.
Medicare’s guaranteed issue overview is here: Your right to buy a Medigap policy
What If You Missed Your Window Already?
Do not assume the answer is automatically no.
You may still be able to buy a Medigap plan, but the next step depends on why you missed the window and whether you have any guaranteed issue rights.
I would look at three things first:
- when your Part B actually started
- whether you have had a recent coverage change that creates a guaranteed issue right
- whether you are comfortable with underwriting if no special protection applies
If you are still early in your Medicare decision, use the Medicare Readiness Checklist before you lock yourself into the wrong path.
What I Tell Kansas City Area Clients
Around Blue Springs, Lee’s Summit, Independence, and the wider Kansas City metro, this comes up in two common situations:
- someone keeps working after 65 and assumes all Medicare deadlines start later automatically
- someone chooses Medicare Advantage first without understanding how hard Medigap can be to get later
Neither mistake is rare. Both are preventable if you look at the Part B start date before you enroll in anything else.
Should You Buy Medigap During Open Enrollment?
If you want Medigap, that window is usually your cleanest shot.
That does not mean Medigap is always the right answer. Some people are better served by Medicare Advantage based on budget, provider use, and risk tolerance.
But if you think you may want the provider freedom and predictable cost structure of Medigap, it is worth deciding during your open enrollment period instead of assuming you can circle back later.
For the broader comparison, read Medicare Advantage vs Medigap in the Kansas City Area: Which Is Right for You?
The Bottom Line
Medigap open enrollment starts the first month you are 65 or older and enrolled in Part B. It lasts 6 months, and it is usually the best time to buy a supplement because health history generally cannot be used against you then.
The biggest mistake is treating Medigap like a decision you can safely postpone. Sometimes you can. Sometimes postponing closes the easiest door you had.
Frequently Asked Questions
When does Medigap open enrollment start?
It starts the first month you are both 65 or older and enrolled in Medicare Part B.
How long does Medigap open enrollment last?
It lasts 6 months from the month it begins.
Can I buy Medigap later if I miss open enrollment?
Sometimes yes, but you may have to go through medical underwriting unless you have a guaranteed issue right.
Does Medigap open enrollment start when I turn 65 or when Part B starts?
It starts when both are true. Turning 65 alone does not start the window if Part B has not started yet.
If I keep working after 65, do I lose my Medigap open enrollment chance?
Not automatically. If you delay Part B because you have qualifying employer coverage, your Medigap open enrollment window usually starts later when Part B begins.