This guide explains Medicare Supplement Enrollment Periods—Open Enrollment, Guaranteed Issue, and state-specific rules—so you can enroll with confidence and avoid costly mistakes.
Why Medicare Supplement Enrollment Rules Matter More Than You Think
If there’s one thing that frustrates me more than anything in this industry, it’s the amount of confusing or flat-out wrong information people get when trying to make their Medicare decisions. I’ve spent over 20 years helping people avoid costly mistakes, and I’ve seen what happens when someone unknowingly misses their window to enroll in a Medicare Supplement plan. Spoiler alert: it’s not pretty—and it’s usually not fixable.
Let me give you a real example.
A woman named Janice from Pennsylvania called me a few months ago. She had just turned 67 and was coming off her employer’s health insurance plan. She assumed she could just “pick up a Medigap Plan G” without any hassle. But when we started the application process, she hit a wall—she had missed her guaranteed issue window by just a few weeks. Because of a recent heart condition, no carrier would accept her.
It broke my heart to tell her that her best options had vanished simply because no one had explained the rules to her clearly. That’s why I wrote this post.
In this article, I’m going to break down every Medicare Supplement enrollment rule—plain and simple. Whether you’re turning 65 soon, retiring later, or already enrolled and thinking of switching plans, I’ll help you know:
- When you’re protected from being denied or overcharged
- Which states give you extra flexibility
- What to watch out for if you’re switching from Medicare Advantage
- And how to avoid the top mistakes people regret the most
Let’s cut through the clutter and get you the facts you actually need—without fluff, without sales pressure, and without surprises down the road.
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Medicare Supplement Open Enrollment Period
Let’s start with the most important window: your Open Enrollment Period.
This is a special 7-month window that starts the month you turn 65 and are enrolled in Medicare Part B. It's your golden ticket to choose any Medicare Supplement (also called Medigap) plan you want—no health questions asked.
Here’s an example:
If your 65th birthday is in July and you start Medicare Part B that same month, your Open Enrollment Period runs from April 1 through October 31. During this time, insurance companies must accept you—even if you have health problems.
Once this period ends, insurance companies can ask health questions and may deny coverage or charge you more based on your health.
Why this matters:
Many people think they can sign up for a Medicare Supplement anytime without a problem. That’s not always true. Outside of this window, it’s harder to qualify—especially if you have health issues.
So if you’re turning 65 soon, or just started Part B, this is the best time to lock in the plan you want.
Guaranteed Issue Rights for Medicare Supplement Plans
| Situation | What It Means | Your Rights |
|---|---|---|
| Trial Right – Medicare Advantage | You enrolled in a Medicare Advantage plan when first eligible. | You can switch to a Medigap plan within 12 months. No medical underwriting. |
| You previously had a Medigap plan | You tried Medicare Advantage for the first time and want to go back. | You may be able to get your old Medigap plan back, even with health issues. |
| Your Medicare Advantage or SELECT plan leaves your area | Your plan is discontinued or no longer available in your ZIP code. | You can buy a Medigap plan with Guaranteed Issue rights. |
| Your plan breaks Medicare rules | The insurance company didn’t follow CMS guidelines. | You are entitled to switch to a Medigap plan with no health questions. |
| Your insurance company goes bankrupt | Your plan stops operating. | You have a Guaranteed Issue right to get a Medigap plan. |
| Losing employer coverage after age 65 | You delayed Medicare due to creditable job-based coverage. | You get a 63-day window to enroll in a Medigap plan without underwriting. |
Guaranteed Issue Situations
Let’s say you missed your Open Enrollment Period—but don’t panic! You might still have a Guaranteed Issue (GI) right.
What does "Guaranteed Issue" mean?
It means insurance companies can’t deny you a Medicare Supplement plan, even if you have health issues. They also can’t charge you more because of your health. But unlike Open Enrollment, you might have fewer plan choices.
Here are some common situations where Guaranteed Issue rights apply:
- You try Medicare Advantage, but change your mind.
If you leave a Medicare Advantage plan within your first year, you get a Trial Right to go back to a Medicare Supplement plan. This is like a free "do-over." - You move out of your plan’s service area.
If you move and your plan doesn’t cover the new area, you can switch to a Medigap plan without medical questions. - Your plan is terminated or breaks the rules.
If your insurance company goes out of business or violates Medicare rules, you may qualify for a GI right.
👉 Important:
In these situations, you may not get to pick any Medigap plan—just a few specific ones (like Plan A, B, D, G, K, or L). It depends on where you live.
✅ Not sure if you qualify? We can help you check.
Book your free Medicare Supplement review today and get peace of mind knowing you’re covered
States with a Birthday Rule for Medicare Supplement Changes
Here’s a cool rule you might not know about—the Birthday Rule. It gives people in certain states a chance to switch their Medicare Supplement (Medigap) plan every year around their birthday—no health questions asked.
How does it work?
Let’s say you live in California and have a Plan G. Around your birthday each year, you can shop around for another Plan G from a different insurance company—even if your health has changed. You don’t have to go through medical underwriting.
This rule helps you look for a better price or a company with better service, without worrying about being denied coverage.
These states have a Birthday Rule:
- California
- Oregon
- Illinois
- Idaho
- Nevada
Each state has slightly different time windows—some give you 30 days, others up to 60—so it’s smart to double-check the rules where you live.
Quick Tip:
The Birthday Rule only works if you’re staying with the same plan type—like switching from Plan G to another Plan G, or Plan N to another Plan N.
🎂 Your birthday could be a gift that saves you money. Want to see if you qualify for a better rate?
Let’s take a look together →
States with Year-Round Open Enrollment
Some states go above and beyond to protect their Medicare-eligible residents. If you live in one of these Year-Round Open Enrollment states, you can apply for a Medicare Supplement (Medigap) plan at any time of the year—and you can’t be denied due to your health.
No deadlines. No medical questions. Just freedom.
That’s right—there’s no special window you have to wait for. You can apply anytime, and the insurance company must accept you.
These special states are:
- New York
- Connecticut
- Vermont
- Washington
- Oklahoma
This kind of flexibility is very rare. Most states only offer guaranteed enrollment when you first sign up for Medicare, or in limited situations like losing coverage.
If you live in one of these states, consider yourself lucky—you have more freedom and control over your healthcare choices than most.
🗽 Live in a year-round state? Want to switch your plan or see if you can save money?
Book your free Medicare Supplement review today and get peace of mind knowing you’re covered—on your terms.
Missouri’s Anniversary Rule
If you live in Missouri, you’ve got a unique advantage when it comes to changing your Medicare Supplement plan. Missouri has something called the Anniversary Rule.
Here’s how it works:
- Every year, you get a 60-day window around the anniversary of your Medigap policy.
- During that time, you can switch to the same plan (like Plan G to Plan G) from a different insurance company.
- Best part? No health questions. No medical underwriting.
So, if you find a better rate with another company—or if you just want better service—you don’t have to stay stuck.
👉 Why it matters: It gives you a fresh chance each year to get the same coverage for possibly a better price—even if your health has changed.
Maine’s Annual Open Enrollment
Maine is another state that offers its residents a special kind of freedom.
In Maine, anyone with a Medigap policy can:
- Switch to a different Medigap plan or company once per year
- Do it without answering any health questions
This means even if you’ve had health changes since first signing up, you can still shop around for better coverage or pricing.
👉 Why it matters: In most states, switching plans later could mean getting denied due to your health. But in Maine, you get a second chance every year.
Final Thoughts: How to Protect Your Medicare Supplement Rights
Choosing the right Medicare Supplement plan isn’t something you want to put off or guess at. Throughout this article, we’ve looked at the most important enrollment periods that can impact your coverage and costs:
- Open Enrollment Period – the best time to enroll without health questions
- Guaranteed Issue Situations – special times when you're protected, even outside of open enrollment
- Birthday Rule States – where you can switch plans near your birthday
- Year-Round Open Enrollment States – a rare benefit that lets you apply anytime
- Missouri’s Anniversary Rule – giving you a yearly chance to switch companies
- Maine’s Annual Open Enrollment – offering a no-questions-asked switch once a year
But here’s the bottom line:
👉 If you wait too long, or don’t know your state’s rules, you could lose your right to switch or be denied coverage altogether.
This stuff gets complicated fast, and unfortunately, a lot of people don’t find out until it’s too late.
The good news? You don’t have to figure it out alone.
We’ve helped hundreds of people just like you understand their options—and we’d be happy to help you too.
| Enrollment Scenario | What You Need to Know |
|---|---|
| Medigap Open Enrollment Period (OEP) | A 6-month window that starts when you’re 65 and enrolled in Medicare Part B. During this time, insurers can’t deny coverage, raise rates, or delay coverage due to your health. |
| After OEP | You can still apply for Medigap anytime, but insurers can use medical underwriting. They may deny coverage or charge more based on your health. |
| Guaranteed Issue Rights | Certain events like losing employer coverage, your plan exiting the area, or your carrier violating rules may give you rights to enroll without health questions. |
| Trial Period | If you try a Medicare Advantage plan when first eligible, you get a 12-month trial. You can switch back to Original Medicare and buy a Medigap plan without underwriting. |
| State-Specific Rules | Some states offer annual or birthday-based switching (like California or Missouri) where you can change Medigap plans without medical questions. |
If you’re moving to a new state or ZIP code, it could affect your Medigap options—learn what happens to your Medicare coverage when you move.
Faq About Medicare Supplement Enrollment
The main enrollment period for a Medicare Supplement plan—also known as the Medigap Open Enrollment Period—is a 6-month window that begins when you are both 65 or older and enrolled in Medicare Part B. During this time, insurance companies must accept you without asking health questions or charging you more based on medical history.
The 6-month rule refers to your one-time Medigap Open Enrollment Period. It starts the month your Medicare Part B becomes active and lasts for 6 months. During this period, you have guaranteed rights to buy any Medigap plan sold in your state without being denied or charged more due to your health.
There are three key enrollment periods in Medicare:
-
Initial Enrollment Period (IEP) – A 7-month window around your 65th birthday to sign up for Medicare Part A and B.
-
Annual Enrollment Period (AEP) – Runs from October 15 to December 7 each year. You can switch Medicare Advantage or Part D plans during this time.
-
Special Enrollment Periods (SEP) – Triggered by life events like losing job-based coverage or moving to a new state.
🔎 Note: These refer to Medicare Parts A, B, C, and D — not Medigap. Medicare Supplement plans follow separate rules.
✅ Don’t risk being denied coverage.
Book your free Medicare Supplement review today and get peace of mind knowing you’re covered—on your terms.
About the Author
David Scallion is a licensed Medicare advisor and the founder of Lehigh Partners Senior Benefits. With over 20 years of experience helping seniors navigate Medicare with clarity and confidence, David is known for his no-pressure, educational approach. He’s passionate about making complex topics simple and ensuring every client gets the coverage that fits their needs—without the confusion.
When he’s not on the phone helping clients, you’ll find him creating helpful resources, writing about Medicare trends, or enjoying iced coffee with a good dose of dad humor. Learn more.
