If you're new to Medicare
Your window opens the day Part B starts, not your 65th birthday.
You generally have six months of guaranteed issue protection, meaning insurers typically can't require health questions or deny coverage based on your medical history.
If you've already missed it
You can still apply — approval isn't guaranteed outside your window.
Guaranteed issue rights and state-level protections may still help.
One rule to remember: your Medigap Open Enrollment Period begins when Medicare Part B becomes effective — not when you turn 65.
Turn 65
→
Part B Starts
→
6-Month Medigap OEP
→
Medical Underwriting May Apply
Scenario 1: Part B Starts at 65
- Turn 65
- Part B becomes active → OEP begins
- Six-month window
- Underwriting generally begins after
Scenario 2: Delayed Part B (Employer Coverage)
- Turn 65, stay on employer plan
- Part B becomes active later → OEP begins
- Six-month window
- Underwriting generally begins after
What Is the Medigap Open Enrollment Period?
The Medicare Supplement (Medigap) Open Enrollment Period is a six-month window that begins the first day of the month you're both 65 or older and enrolled in Medicare Part B.
This is your single most important opportunity to enroll in a Medigap plan.
During this period, you have specific federal protections.
- You can purchase any Medigap plan available in your area.
- Insurers generally can't require you to answer health questions.
- Insurers generally can't deny you coverage based on your health.
- Insurers generally can't charge you more for a pre-existing condition.
This protection is confirmed on Medicare.gov's Medigap basics page.
When Exactly Does It Start?
The Medigap Open Enrollment Period doesn't automatically start when you turn 65.
It only begins once both conditions are met: you're 65 or older, and your Part B coverage is active.
This is one of the most common Medicare misunderstandings we see because many people assume their 65th birthday automatically starts every Medicare enrollment window.
Your six-month clock starts on the first day of that month, per Medicare.gov's guide to when you can buy a Medigap policy.
Example: You turn 65 in June.
Your Part B becomes active July 1.
Your window runs July 1 through December 31.
What If You Delayed Part B for Employer Coverage?
Many people work past 65 and stay on an employer plan, delaying Part B along the way.
If that's you, your window doesn't start at 65.
It starts when Part B becomes active.
Example: You turn 65 but keep working until 67.
Part B starts October 1.
Your window runs October 1 through March 31.
Even though you're older than 65, you still get the full six-month guaranteed issue protection.
Real-Life Scenarios
Timing and personal circumstances matter here more than the rules alone suggest, so a few scenarios usually make this click.
Linda: Retiring at 65
Situation: Turns 65 in July and retires.
Result: Her Part B begins July 1, so her Medigap Open Enrollment Period runs through December 31 — six months to enroll in any Medigap plan available to her without medical underwriting.
John: Working Past 65
Situation: Keeps employer coverage until age 67.
Result: His six-month Medigap Open Enrollment Period doesn't begin until Part B becomes effective — not at 65.
Rachel: Leaving Medicare Advantage
Situation: Enrolls in a Medicare Advantage plan at 65, then decides she wants Original Medicare and Medigap instead.
Result: A "trial right" can give her guaranteed issue access if she applies within 12 months of joining the Advantage plan.
Tom: Moving to a New State
Situation: Enrolled in Medigap in Arizona at 65, then moved to Connecticut two years later.
Result: His federal window has long closed, but Connecticut's year-round protections may still let him switch plans without underwriting.
How It Differs From Other Medicare Enrollment Periods
People often confuse Medigap Open Enrollment with the Annual Enrollment Period or the Medicare Advantage Open Enrollment Period. They aren't the same thing.
| Enrollment Period | Applies To | Underwriting? | Every Year? |
|---|
| Medigap OEP | Medicare Supplement | None during the window | No — one time only |
| Annual Enrollment | Medicare Advantage & Part D | Not applicable | Yes (Oct 15 – Dec 7) |
| MA OEP | Medicare Advantage | Not applicable | Yes (Jan 1 – Mar 31) |
Your Medigap window is personal to you and tied to your own Part B start date — it doesn't reset every year like the other two.
What If You Missed Your Window?
Can you still apply? Yes.
You can apply for or switch a Medigap plan any time of year — there's just no guarantee of approval outside your OEP or a guaranteed issue period.
Can you be denied? In most states, yes, based on your answers to medical underwriting questions.
Do some companies approve people anyway? Often.
Underwriting standards vary a lot by carrier, and people with moderate health conditions sometimes still get approved.
What about guaranteed issue rights? These are limited, time-sensitive situations — such as losing other coverage or leaving a Medicare Advantage plan within your trial period — where insurers must accept your application without underwriting.
Medicare's official Medigap guide outlines these rights.
You can also switch Medigap plans outside your OEP at any time of year.
Outside your original window, though, insurers can generally require underwriting unless you qualify for a special situation — so getting approved for a new plan before canceling your current one is the safer order of operations.
States With Extra Medigap Rights
Federal law generally gives most people one Open Enrollment Period. Several states go further, offering protections that make changing Medigap plans easier down the road.
These state rules don't replace the federal Medigap Open Enrollment Period — they provide additional opportunities to enroll or switch plans in certain situations.
A growing number of states provide Medigap protections beyond the federal minimum.
Some allow current policyholders to switch plans during a birthday or anniversary window, while a smaller number provide broader annual or year-round enrollment rights.
Eligibility, timing, and available plan changes vary significantly by state.
Examples of states with additional protections include:
- Connecticut and New York — broad year-round protections
- California, Oregon, Illinois, and Louisiana — more limited switching opportunities for qualifying existing policyholders
From the Field
One misconception we regularly hear is that moving to another state automatically gives someone a brand-new Medigap Open Enrollment Period.
In reality, your rights depend on the laws of the state you're moving to. Some states provide ongoing protections, while others follow only the federal rules.
Clients are sometimes surprised their new state has completely different Medigap rules than the one they left.
If a move is part of your retirement plan, it's worth checking your destination state's rules before finalizing your Medigap plan, not after.
Common Medigap Open Enrollment Mistakes
- Thinking the window starts on your 65th birthday instead of your Part B effective date.
- Waiting until you're already sick or dealing with a new diagnosis to enroll.
- Confusing Medigap OEP with Medicare's Annual Enrollment Period.
- Canceling old coverage before new coverage is actually approved.
- Assuming you can switch Medigap plans anytime without underwriting.
When It Makes Sense to Talk to a Medicare Agent
Medigap timing rules are specific, and once your window closes, the stakes get higher.
A few situations where talking to a licensed agent tends to be worth it:
- You're approaching Medicare for the first time and want to confirm your exact window.
- You've already missed your OEP and want to understand your realistic options.
- You're comparing carriers and want current pricing for your ZIP code.
- You have underwriting questions after a health change.
- You're moving to a new state and want to know how that affects your Medigap rights.
An experienced agent can confirm your Part A and B effective dates, calculate your exact six-month window, and compare pricing across the carriers competing in your area.
Bottom Line
The Medigap Open Enrollment Period is your one-time opportunity to enroll in a Medicare Supplement plan without medical underwriting or the risk of being denied because of your health.
It starts when you're 65 or older and enrolled in Part B, and it lasts six months.
Once this window closes, getting a plan can become more complicated, especially if you have health conditions insurers weigh when deciding whether to approve your application.
If you've already missed it, guaranteed issue rights or your state's own rules may still open a door — it's worth checking before assuming you're out of options.
Before your window begins, here's what's worth having in place:
- Know your Part B effective date
- Compare carriers before your window starts
- Decide which plan letter fits your situation
- Apply during your six-month window
