Key Takeaways

• Missing Medicare enrollment deadlines or choosing the wrong timing can lead to lifetime penalties and gaps in coverage.

• Understanding which parts of Medicare you need and when to enroll is essential to avoid higher costs and limited access to care.

Why Medicare Enrollment Still Trips People Up in 2025

Enrolling in Medicare may seem straightforward at first glance, but thousands of Americans still make preventable mistakes every year. With multiple enrollment periods, penalties that never go away, and coverage gaps you might not realize until it’s too late, it’s no wonder the process continues to cause confusion.

In 2025, more beneficiaries than ever are reaching Medicare eligibility age, making it critical to understand what to do—and what to avoid—when you first become eligible.

Understanding the Different Enrollment Periods

Timing is everything with Medicare. If you don’t sign up at the right time, you may face coverage delays, permanent penalties, or higher costs. Here’s what you need to know:

Initial Enrollment Period (IEP)

• When it happens: The 7-month period starting three months before your 65th birthday, including the month you turn 65, and ending three months after.

• What you can do: Enroll in Medicare Part A and/or Part B. You can also select a Part D drug plan or Medicare Advantage plan if applicable.

• What happens if you miss it: Delaying Part B enrollment without other qualifying coverage can trigger a lifelong late enrollment penalty.

General Enrollment Period (GEP)

• When it happens: Every year from January 1 to March 31.

• Who it’s for: Those who missed their IEP and don’t qualify for a Special Enrollment Period.

• Coverage starts: July 1 of the same year.

Special Enrollment Period (SEP)

• When it applies: If you’re still working and covered under an employer group health plan when you turn 65, you may delay Part B without penalty.

• SEP window: You have 8 months from the end of employment or the end of the group plan—whichever comes first—to sign up for Part B.

Annual Enrollment Period (AEP)

• When it occurs: October 15 to December 7 every year.

• What you can do: Change from Original Medicare to Medicare Advantage or switch/drug coverage.

1. Missing the Initial Enrollment Period

Many people assume that Medicare enrollment happens automatically at age 65. While that’s true if you’re already receiving Social Security benefits, it’s not the case if you’re delaying Social Security. In that situation, you need to actively sign up for Medicare. If you miss the IEP, you’ll be left with delayed coverage and penalties.

2. Not Signing Up for Part B When You Should

Part B covers outpatient care and doctor visits. Some individuals delay Part B because they think they don’t need it, or because they are still working. However, if your coverage through work doesn’t qualify as creditable coverage, you could face a penalty for every 12-month period you delay.

The penalty adds 10% to your Part B premium for each full year you delay enrollment—permanently.

3. Assuming Employer Coverage Lets You Off the Hook

If you’re still working at 65, you might think you don’t need to enroll in Medicare at all. That’s only partially true. Your current health plan must qualify as creditable under Medicare rules. If it doesn’t, and you delay Part B or Part D, you’ll face penalties.

Always check with your employer’s HR department to confirm your plan’s Medicare status.

4. Forgetting About Part D Prescription Coverage

Prescription drugs aren’t covered under Original Medicare. To avoid paying full price for medications—and a potential late enrollment penalty—you need to enroll in a Part D plan during your IEP unless you have other creditable drug coverage.

The Part D penalty adds 1% of the national base premium to your monthly cost for every month you delay enrollment after your IEP.

5. Confusing Medicare Advantage With Supplement Plans

Medicare Advantage and Medigap (supplement plans) are often confused, but they serve very different purposes. You cannot have both at the same time. Medicare Advantage (Part C) replaces Original Medicare, while Medigap supplements Original Medicare.

Choosing the wrong type of plan—or assuming one includes the other—can lead to denied coverage or unexpected out-of-pocket costs.

6. Ignoring Out-of-Pocket Costs in Advantage Plans

Medicare Advantage plans may seem attractive because they often have lower upfront costs. But these plans come with networks, copays, and maximum out-of-pocket limits that can surprise you later.

In 2025, the maximum out-of-pocket limit for in-network care in Medicare Advantage is $9,350, with up to $14,000 for combined in- and out-of-network services. Many enrollees don’t realize this until they need care.

7. Missing the Medicare Supplement Enrollment Window

If you choose Original Medicare and want a Medigap plan, your best time to buy is during your 6-month Medigap Open Enrollment Period. It starts the month you’re 65 or older and enrolled in Part B.

During this window, insurance companies must sell you a policy, regardless of your health. After it ends, you could be denied coverage or charged more based on medical history.

8. Assuming Coverage Starts Immediately

Medicare coverage start dates depend on when you enroll. Enrolling early in your IEP means coverage starts the month you turn 65. But if you enroll during or after your birth month, your coverage may be delayed by one to two months.

This can leave you without coverage, particularly if you drop other insurance assuming Medicare begins instantly.

9. Not Reviewing Annual Plan Changes

Even if you’re already enrolled, Medicare isn’t a set-it-and-forget-it system. Plan premiums, benefits, provider networks, and drug formularies can change every year.

From October 15 to December 7, during the Annual Enrollment Period, you can switch plans. Ignoring this window could mean you’re stuck with:

• A more expensive plan

• A plan that no longer covers your medications

• A network that dropped your doctor

10. Assuming Spousal Coverage Automatically Transfers

Medicare is individual coverage. If your spouse turns 65 and becomes eligible, they need to enroll separately—even if you’re both on the same employer or retirement plan currently. Assuming otherwise can leave your spouse without coverage.

What to Do If You’ve Already Made a Mistake

If you believe you’ve missed a Medicare deadline or chosen the wrong coverage, take immediate steps:

• Check for eligibility under a Special Enrollment Period. Life events like job loss, moving, or losing coverage may give you another chance to enroll.

• Contact Social Security or Medicare directly to clarify your status.

• Speak with a licensed agent who can walk you through your current options.

Some mistakes can be corrected—others may carry lasting consequences. But acting quickly can help minimize penalties and avoid coverage gaps.

How to Stay Ahead of Enrollment Mistakes

• Mark your calendar: Be aware of your IEP, AEP, and SEP windows.

• Understand the coverage types: Know the difference between Original Medicare, Medicare Advantage, Part D, and Medigap.

• Check your current insurance: If you’re working, verify whether your employer plan is creditable.

• Review your plan annually: Ensure your doctors, medications, and out-of-pocket limits still meet your needs.

Protecting Your Medicare Future Starts With Better Decisions

The stakes with Medicare enrollment are too high to leave to chance. A missed deadline or misunderstood rule can cost you thousands—or worse, leave you without essential health coverage.

If you’re unsure where to begin or how to correct a mistake, reach out to a licensed agent listed on this website. Their expertise can help you sort through timelines, options, and coverage details that are easy to overlook on your own.