Medicare Enrollment Periods: When to Enroll and When to Make Changes?
Medicare offers several enrollment opportunities throughout the year, but not all are created equal. Some are initial windows when you become eligible, while others are reserved for corrections, plan switches, or unique life circumstances.
Medicare is a foundational part of retirement planning, but understanding when to enroll – and when you can or should make changes – can feel overwhelming. The system involves multiple enrollment periods, each with its own rules, deadlines, and consequences.
Missing a critical window could result in lifelong penalties or coverage delays that could jeopardize one’s health or finances.
In this comprehensive guide, we’ll explain each Medicare enrollment period in detail, including:
- What each window is for
- When it occurs
- How to take action
You’ll also find explanations of common exceptions, suggestions for navigating your choices, and real-life examples that highlight the importance of getting these decisions right.
Let’s take a quick look at the key Medicare dates you need to know.
Overview of Enrollment Periods
| Enrollment Period | Timeframe | Purpose |
|---|---|---|
| Initial Enrollment Period (IEP) | 3 months before to 3 months after your 65th birthday month | Enroll in Medicare Part A and/or Part B for the first time |
| General Enrollment Period (GEP) | January 1 – March 31 | Enroll in Part A and/or Part B if you missed your IEP |
| Medigap Open Enrollment | 6 months starting when you enroll in Part B | Purchase Medicare Supplement (Medigap) without medical underwriting |
| Medicare Advantage OEP | January 1 – March 31 | Switch or drop Medicare Advantage plans |
| Annual Election Period (AEP) | October 15 – December 7 | Make changes to your Medicare Advantage or Part D plan |
| Special Enrollment Periods (SEP) | Varies by situation | Enroll or change plans due to specific life events |
Each of these periods plays a different role in your Medicare journey. Let’s explore each one in more depth.
Initial Enrollment Period (IEP)
Your Initial Enrollment Period is the first time you’re eligible to sign up for Medicare, and for most people, it begins as they approach age 65.
This seven-month window includes:
- Three months before the month you turn 65
- Your birthday month
- Three months after your birthday month
This is the best time to enroll in Medicare Part A and Part B.
Part A generally covers inpatient hospital care and is premium-free for most individuals, while Part B covers outpatient services and comes with a monthly premium.
Failing to enroll during your IEP could result in late enrollment penalties for Part B and delayed access to health services. However, there are exceptions.
If you’re still working and have creditable health insurance through your employer or spouse’s employer, you may be eligible to delay Part B without penalty.
In that case, you may still choose to enroll in Part A during your IEP since it typically has no cost.
This window is also when your effective coverage date is most flexible. The earlier you enroll within the IEP, the more likely your coverage will begin by your 65th birthday month or shortly after.
Part A Late Enrollment Penalty
Most people qualify for premium-free Part A based on their work history. However, if you don’t and delay enrollment, your premium may increase by 10%, and you’ll pay the higher amount for twice the number of years you delayed enrollment.
These penalties are avoidable – but only if you act during your Initial Enrollment Period or qualify for a Special Enrollment Period.
Part B Late Enrollment Penalty
If you delay enrolling in Part B for 12 or more months after you were first eligible, you will face a 10% increase in your monthly Part B premium for each full 12-month period that you delayed.
This penalty is not a one-time fee – it applies for as long as you have Part B.
For example, if you were eligible for Medicare at 65 but didn’t sign up until you were 68, and you had no other creditable coverage during that time, you would pay a 30% higher premium for Part B every single month.
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Good to Know:
If you are already receiving Social Security benefits when you turn 65, you will automatically be enrolled in Medicare Part A and Medicare Part B.
Disability Cases: If you are disabled and receive Social Security Disability insurance benefits (SSDI) or Railroad Retirement Board benefits, your IEP will begin on your 65th birthday OR when you receive your 24th disability benefits payment from Social Security or Railroad Retirement, whichever is earlier.
Children between the ages of 18 and 20 who receive SSDI based on a disability they first developed before age 18, as reflected by an IEP, can also qualify for Medicare.
End-Stage Renal Disease (ESRD) Cases: If you are diagnosed with ESRD, as long as you have applied and met the earnings requirements for SSDI, your Medicare enrollment may begin as follows:
- Three months after you first began a regular dialysis course, or
- The first month of a regular dialysis course, if you went through self-dialysis training, or
- The month you receive a kidney transplant, or
- Two months before a kidney transplant, if you were hospitalized to prepare for your transplant during that time
Note: A minor child with end-stage renal disease can also qualify for Medicare based on their parents’ work credits.
Lou Gehrig’s Disease (amyotrophic lateral sclerosis or ALS) Cases: If you are diagnosed with ALS, your disability and Medicare eligibility for enrollment are immediate.
General Enrollment Period (GEP)
The General Enrollment Period (GEP) exists as a crucial fallback for individuals who missed their Initial Enrollment Period (IEP) and who do not qualify for a Special Enrollment Period (SEP).
Although it’s a lifeline, enrolling during this period can have significant drawbacks, including late penalties and delayed coverage.
The General Enrollment Period occurs annually from January 1 to March 31. During this time, individuals who failed to sign up for Medicare Part A and/or Part B during their Initial Enrollment Period can apply for coverage.
This window is specifically designed for people who:
- Did not enroll in Medicare when they first became eligible at age 65 (or based on disability)
- Are not eligible to enroll under a Special Enrollment Period due to loss of other health insurance or qualifying life events
Enrollment during the GEP allows you to sign up for Original Medicare – that is, Part A (hospital insurance) and/or Part B (medical insurance). However, your coverage does not start right away.
No matter when you enroll between January and March, your Medicare benefits will not begin until July 1 of the same year.
This delay can leave you without health insurance for several months if you are not covered under another plan.
For example, if you apply for Part B on January 5th, you must still wait until July 1st for it to take effect. That’s a six-month gap in care – and a risky period to go uncovered, especially in later years of life.
Real-Life Example: John’s Costly Delay
Let’s say John, a self-employed consultant, turned 65 in April 2021. He assumed he didn’t need Medicare right away because he was healthy and planned to continue working. He also wasn’t enrolled in any employer-sponsored health plan, which means he did not have creditable coverage.
John forgot about Medicare altogether until February 2024 – nearly three years later – when he started having health issues. He enrolled during the GEP in February, but his coverage didn’t start until July 1, 2024, leaving him without coverage for several months.
He also faced a 30% penalty on his Part B premium that will follow him for the rest of his life. If the base premium is $185/month, John now pays an additional $55.50/month – or $666 annually – for as long as he has Medicare.
What Can’t You Do During the GEP?
It’s equally important to understand what the General Enrollment Period does not allow:
- You cannot enroll in a Medicare Advantage (Part C) plan or a Part D prescription drug plan directly during the GEP.
- You may, however, enroll in a Medicare Advantage or Part D plan after your Original Medicare becomes active in July, provided you are eligible for a Special Enrollment Period or the MA enrollment window tied to GEP.
This means if you need comprehensive drug coverage or the managed care benefits of a Medicare Advantage plan, your options will be limited until after July 1, and only if other conditions are met.
Should You Wait for the General Enrollment Period?
In most cases, the answer is no. The GEP should be seen as a last resort.
Relying on it puts you at risk of going uninsured for months and incurring unnecessary costs. The best time to enroll is during your Initial Enrollment Period or a Special Enrollment Period, if applicable.
The only time the GEP makes sense is if you truly missed your IEP and have no alternative coverage. Even then, you should act as early in the GEP window as possible to minimize the waiting period.
Medicare Supplement (Medigap) Open Enrollment
Once you’re enrolled in Medicare Part B, a unique six-month window opens that provides you with rights and protections unlike any other point in your Medicare journey.
This window is known as the Medigap Open Enrollment Period, and it is your best (sometimes only) chance to enroll in a Medicare Supplement (Medigap) plan without facing medical underwriting.
Medigap policies, sold by private insurance companies, help pay for the costs that Original Medicare doesn’t cover – things like deductibles, copayments, and coinsurance.
Note: These plans do not include prescription drug coverage, which is handled separately through Part D.
When Does the Medigap Open Enrollment Period Begin?
This enrollment period begins on the first day of the month in which you are both:
- Age 65 or older and
- Enrolled in Medicare Part B
The window remains open for six consecutive months and cannot be repeated. If your birthday is in February and you enroll in Part B that same month, your Medigap Open Enrollment runs from February 1 through July 31.
Why Is This Period So Important?
During this six-month window:
- You cannot be denied coverage based on your health history or pre-existing conditions
- You cannot be charged more due to age, gender, or existing medical issues
- The plan you choose must be issued on a guaranteed-issue basis, meaning you are accepted regardless of your health
Outside this window, Medigap applications are subject to medical underwriting, and insurers can:
- Ask health questions
- Deny your application
- Charge higher premiums based on health status
- Impose waiting periods for pre-existing conditions
For individuals with chronic health issues, this limited enrollment period may be the only chance to lock in affordable, supplemental coverage without risk of denial.
Real-Life Scenario: David’s Missed Medigap Window
David turned 65 in August and enrolled in Part B immediately. However, he assumed he could delay choosing a Medigap plan until he “needed it.”
A year later, after a major heart surgery, David tried to purchase a Medigap policy.
Unfortunately, because he was now outside his OEP, the insurer reviewed his medical records and denied his application due to recent cardiac events.
This scenario underscores the importance of acting during the six-month window – even if you feel healthy now. Once it passes, your options narrow dramatically.
What Happens After the Medigap Open Enrollment Period Ends?
Once the six-month window ends:
- You may still apply for a Medigap plan, but approval is not guaranteed
- Insurers may ask for a health screening
- You may be denied or offered coverage with a higher premium
- If accepted, some policies may exclude coverage for pre-existing conditions for up to six months
These restrictions can make it harder – and more expensive – to get the coverage you want, which is why many Medicare experts urge people to make this decision early and strategically.
Can You Delay Medigap Enrollment?
Yes, but only in limited cases. If you delay enrolling in Medicare Part B (for example, because you have employer coverage), your Medigap Open Enrollment Period is also delayed and will begin when you enroll in Part B later on.
This provides some flexibility, but you must be careful to coordinate the start of your Part B coverage with your Medigap planning.
Medicare Advantage Open Enrollment Period
The Open Enrollment Period for Medicare Advantage (or Part C) plans runs from January 1st to March 31st each year.
A Medicare Advantage (or Part C) plan uses a private insurance company to replace your Part A and Part B coverage, often adding prescription drug coverage as well as other plan benefits.
If you’re already enrolled in a Medicare Advantage (Part C) plan and realize that your current plan isn’t meeting your needs, the Medicare Advantage Open Enrollment Period provides a once-a-year opportunity to make changes.
This window is exclusively for people who are already enrolled in a Medicare Advantage plan and want to switch or drop it.
During this period, you may:
- Switch from one Medicare Advantage plan to another
- Disenroll from a Medicare Advantage plan and return to Original Medicare
- Enroll in a stand-alone Part D (prescription drug) plan if switching back to Original Medicare
This is not the same as the AEP (Annual Election Period). You can’t join a Medicare Advantage plan during this window if you’re not already enrolled in one – you must already be participating in a Medicare Advantage plan to make changes here.
It’s particularly useful for individuals who realize their provider network has changed or who have new healthcare needs that their current plan doesn’t adequately address.
Real-Life Example: Maria’s Mid-Year Shift
Maria, age 69, enrolled in a Medicare Advantage plan during the Annual Election Period. She liked the idea of lower premiums and extra benefits.
However, by February, she found that none of her preferred specialists were in-network and she struggled to get prior authorizations for physical therapy.
During the Medicare Advantage OEP, Maria switched to another plan with broader network access.
Her new coverage began on March 1 – just one month after making the change.
Any changes made during the Medicare Advantage OEP become effective on the first day of the following month. For example:
- A change made on January 20 would take effect on February 1
- A change made on March 10 would take effect on April 1
This timely change allows beneficiaries to quickly pivot if they realize their coverage isn’t working for them.
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Important Tip:
If you are hoping to switch from a Medicare Advantage plan to a Medicare Supplement plan, check to see whether you are still within your Medicare Supplement OEP six-month window (details above) in order to enroll without answering health questions.
If your Medicare Supplement OEP has passed, you may have to answer questions regarding pre-existing conditions, face higher premiums due to underwriting, or possibly be denied coverage.
Annual Election Period (AEP)
Every fall, from October 15 to December 7, the Annual Election Period (AEP) grants Medicare beneficiaries a comprehensive opportunity to review and adjust their coverage.
Changes made during this window take effect January 1 of the following year.
Unlike other Medicare enrollment periods, which are often restrictive or triggered by specific events, AEP is open to all beneficiaries already enrolled in Medicare Part A and/or Part B.
This is the most flexible and widely used enrollment period because it allows beneficiaries to:
- Join a Medicare Advantage plan from Original Medicare
- Switch from Medicare Advantage back to Original Medicare
- Enroll in, switch, or drop a Medicare Part D plan
- Change Medicare Advantage plans
One of the greatest advantages of AEP is that you’re not limited to a single action. You can make multiple changes if you need to, and the most recent election submitted before the December 7 deadline will be the one that takes effect on January 1.
While many assume that doing nothing during AEP will cause no harm, that isn’t always the case. Each fall, insurance companies send out a document called the Annual Notice of Change (ANOC) to let you know how your current plan is changing for the next year.
These changes may involve increased premiums, drug coverage alterations, provider network changes, or revised cost-sharing rules. Failing to review this document – or assuming your plan will remain the same – can lead to unexpected out-of-pocket expenses or even the loss of access to your preferred doctors or medications.
To make the most of AEP, it’s wise to do a thorough annual review of your healthcare needs and compare your current plan with others available in your area. Make sure you compare costs, benefits, and drug coverage options, and working with a licensed agent can streamline the process.
Many people use AEP to adjust their coverage based on new health diagnoses, upcoming surgeries, or a change in financial circumstances.
Missing the AEP deadline, however, means you will be locked into your current plan for another calendar year – unless you later qualify for a Special Enrollment Period (SEP) due to a significant life event like moving, losing other health coverage, or qualifying for Extra Help with Part D.
Real-Life Example: How AEP Can Be a Game-Changer
Consider Margaret, who’s been stable on a Medicare Advantage plan with a $20 monthly drug copay. During AEP, she checked her ANOC and saw her plan would increase copays to $50, and retirements of some pharmacy pharmacies.
She reached out to us to locate a similar MA plan with better coverage and lower copays, enrolling before the December 7 deadline.
Her new benefits began January 1, saving her money and giving access to her local pharmacy.
Should You Always Make a Change?
Not necessarily. The Annual Election Period is not mandatory – if you’re satisfied with your current plan and its upcoming changes, you can let it renew automatically. It is an invaluable opportunity to ensure you get the most value and the right coverage for your circumstances.
But for many, it is the only chance all year to make meaningful changes without restrictions.
Special Enrollment Periods (SEP)
While most enrollment windows are fixed, Special Enrollment Periods (SEPs) are available for individuals who experience qualifying life events. These periods allow for enrollment or plan changes outside of the standard timeframes.
Common reasons for qualifying for a SEP include:
- Losing employer-sponsored or union coverage
- Moving out of your plan’s service area
- Gaining or losing Medicaid eligibility
- Entering or exiting a skilled nursing facility
- Your Medicare Advantage or Part D plan is discontinued in your area
The timing and duration of your SEP will vary depending on your situation. For example, if you lost employer coverage, you typically have an 8-month window to enroll in Medicare Part A and/or Part B, and a 63-day window to enroll in a Part D plan without penalty.
SEPs are a crucial safeguard for people experiencing transitions in care, employment, or residency.
If you are unsure whether you might be eligible for a special enrollment period, you should talk to one of our licensed health insurance agents about your Medicare health plan options.
Our Medicare guides can provide information to help you understand your plan options and qualifications and enroll in an insurance plan that meets your needs within the correct enrollment window.
How to Enroll in Medicare
Applying for Original Medicare is a fairly straightforward process.
You have a few options when you are ready to apply:
- Apply online (this is the fastest option). As you prepare to apply, use the Medicare Documentation Checklist to gather the information you need in order for the process to go smoothly.
- Call the Social Security Administration toll-free at 1-800-772-1213 (TTY 1-800-325-0778).
- Visit your local Social Security office. The agency has a Social Security office locator on its website.
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Pro Tip:
The vast number of plan options and insurance carriers can quickly become overwhelming.
A Medicare guide can quickly narrow down your coverage needs and budget preferences, saving you unnecessary time, energy, and expense.
Once enrolled in Parts A and B, you can start to explore Medigap or Medicare Advantage options.
Bottom Line
Each enrollment window has a specific purpose, and missing the right one can lead to penalties, gaps in coverage, or restricted plan options.
The Initial Enrollment Period (IEP) is your first, and often best, opportunity to enroll in Medicare Parts A and B. If you delay without qualifying for a Special Enrollment Period (SEP), you may face penalties and a wait for coverage until the General Enrollment Period (GEP), which only runs from January 1 to March 31 each year and offers coverage starting July 1.
If you want Medicare Supplement (Medigap) coverage, your one-time six-month window starts when you enroll in Part B. This is your guaranteed issue period – outside of it, you could face denial or higher premiums due to your health status.
For those already enrolled in Medicare Advantage (Part C), the Medicare Advantage Open Enrollment Period allows one annual change from January 1 through March 31. This is your chance to switch plans or return to Original Medicare if your current coverage isn’t working.
Finally, every fall, the Annual Election Period (AEP) from October 15 to December 7 lets you re-evaluate your plan. You can switch between Original Medicare and Medicare Advantage, change your drug coverage, or enroll in new plans. This is your opportunity to adapt your Medicare coverage to your health, financial situation, and provider preferences for the upcoming year.
The key to avoiding costly mistakes is to know your enrollment windows, mark your calendar, and don’t wait until the last minute. Review your options annually, especially during AEP, and consult with a Medicare expert if you’re unsure.
Sources: When Does Medicare Coverage Start? | Medicare Enrollment Periods
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