Key Takeaways
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Missing the correct Medicare enrollment period can lead to permanent penalties and lifelong higher premiums.
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Delaying Part B or Part D without proper employer coverage could result in gaps in care and long-term financial consequences.
Enrolling in Medicare: Why Timing Isn’t Just a Detail
You might assume enrolling in Medicare is automatic or straightforward. But in 2025, the process still includes critical deadlines and exceptions that can leave you paying far more than necessary for the rest of your life. Whether you’re nearing age 65 or delaying retirement, it’s essential to get your enrollment timing right.
Missing your window could mean not just delayed coverage, but late penalties that never go away. Worse, you could be left without needed care when you need it most.
This guide walks you through the most common Medicare enrollment mistakes—and how to avoid them before they become costly.
Mistake 1: Assuming You’re Automatically Enrolled
If you’re already receiving Social Security benefits by the time you turn 65, you are typically enrolled automatically in both Medicare Part A and Part B. But if you haven’t started collecting Social Security yet, you must actively sign up.
Failing to enroll during your Initial Enrollment Period (IEP) could cost you.
Your Initial Enrollment Period:
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Begins three months before the month you turn 65
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Includes your birth month
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Ends three months after that month
If you miss this seven-month window and don’t qualify for a Special Enrollment Period (SEP), you’ll need to wait for the General Enrollment Period—and coverage will be delayed.
Mistake 2: Missing the General Enrollment Period
If you didn’t enroll during your IEP and don’t have employer coverage, your next opportunity is the General Enrollment Period (GEP).
The GEP runs from:
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January 1 to March 31 each year
Coverage starts the month after you sign up. That’s a change from the past, when coverage started in July.
Missing this period means another full year of waiting or going without insurance, plus permanent late penalties for Part B and possibly Part D.
Mistake 3: Delaying Part B Without Creditable Employer Coverage
Many people delay Part B because they’re still working and covered under an employer plan. That can be fine—but only if the coverage qualifies as creditable and comes from an employer with 20 or more employees.
If you delay Part B without meeting these requirements:
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You may pay a 10% penalty for each 12-month period you delayed Part B.
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This penalty is permanent and added to your monthly premium every year.
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Your coverage may also be delayed until the next GEP.
Even if you have retiree insurance, COBRA, or a health plan from the Marketplace, these do not count as creditable coverage for delaying Part B.
Mistake 4: Delaying Part D Prescription Drug Coverage
Just like with Part B, if you don’t sign up for a Medicare drug plan when first eligible and don’t have other creditable prescription coverage, you’ll face late enrollment penalties.
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The penalty is 1% of the national base premium multiplied by the number of full months you delayed enrollment.
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This penalty is added to your monthly premium for life.
Part D penalties apply even if you don’t take any medications when you first become eligible. Unless you have other creditable drug coverage, enrolling on time is the only way to avoid the lifelong surcharge.
Mistake 5: Relying on COBRA or Retiree Coverage
It’s a common trap: you retire at 64, elect COBRA, and assume you can delay Medicare enrollment. Unfortunately, COBRA is not considered creditable coverage for delaying Part B.
If you wait to enroll in Medicare until COBRA ends:
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You may pay a lifelong penalty
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You may have to wait until the next GEP
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You may face a gap in coverage
The same applies to retiree plans that continue after you leave your job. These plans might supplement Medicare, but they don’t replace it.
Mistake 6: Overlooking the Special Enrollment Period Rules
If you or your spouse are working past age 65 and covered by a creditable employer health plan, you may qualify for a Special Enrollment Period (SEP).
This lets you:
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Delay Part B and Part D without penalties
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Enroll in Medicare within 8 months of losing that employer coverage
But here’s the catch: the SEP only applies while you or your spouse are actively working and covered. Once employment or coverage ends, the clock starts ticking. Wait too long, and you’ll lose this penalty-free opportunity.
Mistake 7: Not Reviewing Medicare Advantage or Medigap Enrollment Timing
Original Medicare doesn’t cover everything, so many people add either:
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A Medicare Advantage (Part C) plan, or
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A Medigap supplemental insurance plan
But each has specific enrollment windows:
Medicare Advantage:
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Enroll during your IEP
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Or during the Annual Enrollment Period from October 15 to December 7
Medigap:
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You get a 6-month Medigap Open Enrollment Period starting the month you are 65 or older and enrolled in Part B
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After this window, you may face underwriting or even denial based on health history
Missing these windows means fewer plan options and possibly higher costs later on.
Mistake 8: Not Understanding the Difference Between Enrollment Periods
Medicare has multiple enrollment windows, and each serves a different purpose. It’s easy to confuse them. Here’s a quick recap:
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Initial Enrollment Period (IEP): 3 months before to 3 months after turning 65
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General Enrollment Period (GEP): Jan 1 to Mar 31 if you missed IEP
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Special Enrollment Period (SEP): After employer coverage ends
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Annual Enrollment Period (AEP): Oct 15 to Dec 7 to switch Medicare plans
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Medicare Advantage Open Enrollment Period (MA OEP): Jan 1 to Mar 31 to switch MA plans
Missing one for another could result in penalties or unintended plan changes.
Mistake 9: Forgetting to Enroll in Both Parts A and B for Full Coverage
Some people mistakenly think enrolling in Part A is enough. Part A covers hospital stays, but not outpatient care, doctor visits, or preventive services. That’s what Part B covers.
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You need both Parts A and B for full Original Medicare
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Most other options like Medicare Advantage or Medigap require both as well
If you skip Part B thinking it’s optional, you could be left without essential outpatient coverage—and face penalties when you do sign up later.
Mistake 10: Assuming Late Enrollment Can Be Reversed
Once you miss your Initial Enrollment Period and don’t qualify for a Special Enrollment Period, the late penalties are locked in.
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There’s no appeal for late enrollment penalties unless you qualify for specific exceptions
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You may also face gaps in coverage between the GEP and the start of benefits
That’s why planning ahead is essential—not just for affordability, but to ensure uninterrupted care in retirement.
Being Proactive Pays Off
Understanding Medicare enrollment timelines isn’t just about following rules—it’s about protecting your finances and your access to healthcare for the rest of your life.
Take the time to:
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Understand which enrollment period applies to you
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Confirm your employer or retiree coverage is truly creditable
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Set reminders to review your plan each year
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Get help from a licensed agent if you’re unsure
Avoiding these enrollment mistakes can mean the difference between steady care and steep penalties.
Get Enrollment Right So Your Retirement Stays on Track
Medicare is not automatic for everyone, and mistakes made during your enrollment windows can lead to lifelong penalties or coverage gaps. Whether you’re working past 65 or retiring soon, it’s crucial to match your situation with the correct Medicare enrollment timeline.
Don’t guess your way through Medicare. Get in touch with a licensed agent listed on this website for help evaluating your options, timing your enrollment correctly, and avoiding the missteps that too many retirees regret.
