Key Takeaways

• Missing the Medicare Part B enrollment window can lead to lifelong penalties and coverage delays that affect your health and wallet.

• Signing up at the wrong time, especially if you or your spouse are still working, could mean you’re either paying for duplicate coverage or facing gaps in care.

The Most Overlooked Step in Medicare Enrollment

When you think about Medicare, you probably picture a milestone event tied to turning 65. And while that’s true for many, the reality is far more nuanced. The step people most often miss when enrolling in Medicare is evaluating whether they need to actively sign up for Part B during their Initial Enrollment Period (IEP)—especially if they’re still working or covered under a spouse’s plan.

Failing to make the right move at the right time can lead to penalties that last a lifetime and gaps in your health coverage. Let’s walk through exactly what you need to know—and do—to avoid that misstep.

Your Initial Enrollment Period: Timing Is Critical

The Initial Enrollment Period is your first opportunity to enroll in Medicare. It lasts seven months:

• Starts: Three months before the month you turn 65

• Includes: Your birth month

• Ends: Three months after your birth month

This window applies whether you plan to retire at 65 or not. If you’re not automatically enrolled (which typically happens if you’re already receiving Social Security), then you must sign up manually to avoid delays in coverage.

Working Past 65? You May Need to Sign Up Anyway

A common source of confusion is whether or not you need to enroll in Medicare Part B if you’re still working and have employer coverage. The answer depends on the size of your employer:

• If your employer has 20 or more employees, you can typically delay Part B without a penalty, since your employer’s plan is considered creditable coverage.

• If your employer has fewer than 20 employees, you need to enroll in Part B as soon as you’re eligible, because Medicare becomes your primary insurer.

The same rules apply if you’re covered under a spouse’s insurance. Missing this step means Medicare becomes your primary by default, and if you’re not enrolled, you could end up paying out-of-pocket for services.

Why Part B Is the Most Common Pitfall

Medicare Part B covers medical services like doctor visits, outpatient care, preventive services, and durable medical equipment. But here’s where it gets tricky:

• If you delay enrolling in Part B without having creditable coverage, you’ll face a late enrollment penalty.

• This penalty is permanent and increases your premium by 10% for every 12-month period you were eligible but didn’t sign up.

• You may also have to wait for the General Enrollment Period (January 1–March 31) to sign up, with coverage starting July 1—creating a gap in healthcare.

Creditable Coverage: Know What It Means

To avoid the Part B late enrollment penalty, you need to have creditable coverage. That means your current health insurance must be as good as, or better than, Medicare. Generally, large employer plans and union-sponsored plans meet this standard.

However, COBRA and retiree coverage don’t count as creditable for delaying Part B.

If you’re relying on either, you must still enroll in Medicare Part B when first eligible to avoid penalties.

Special Enrollment Period (SEP): Your Safety Net—But With Limits

If you delayed enrolling in Part B because you had creditable coverage, you get a Special Enrollment Period once that coverage ends. This SEP:

• Lasts 8 months from the end of your employer or union coverage

• Allows you to enroll in Part B without a late penalty

However, the clock starts ticking the moment your employer coverage ends. Waiting too long could result in missing the SEP and facing both a penalty and coverage delay.

The Hidden Risk of Automatic Enrollment Assumptions

Many people assume they’ll be automatically enrolled in Medicare at 65, especially if they’re close to retirement. But unless you’re already receiving Social Security benefits at least four months before your 65th birthday, you won’t be auto-enrolled.

You must actively sign up, and that means knowing your deadlines and acting on them. Don’t let assumptions replace action.

How to Enroll in Medicare the Right Way

To make sure you don’t miss the most critical step, here’s how to get it right:

• Step 1: Understand your IEP window and mark the start and end dates

• Step 2: Evaluate your current health insurance to determine if it qualifies as creditable coverage

• Step 3: If you’re not automatically enrolled, apply for Medicare through the Social Security Administration—either online, by phone, or at a local office

• Step 4: If you’re delaying Part B, keep documentation of your creditable coverage for when you eventually enroll

Late Enrollment Isn’t Just a Penalty—It’s a Compounding Problem

It’s not just the financial hit of the penalty that stings. Delaying Part B without proper coverage can lead to these issues:

• Coverage gaps: You may be without medical coverage for months.

• Out-of-pocket costs: You’ll be responsible for 100% of the cost of care if Medicare was supposed to be your primary.

• Limited enrollment windows: You may have to wait for the General Enrollment Period, which only comes once a year.

Medicare Enrollment in 2025: What’s New

While the core rules haven’t changed dramatically, it’s important to note the 2025 context:

• The General Enrollment Period still runs from January 1 to March 31, with coverage starting July 1.

• The Initial Enrollment Period remains unchanged in structure and timeline.

• More educational tools are now available through the Social Security website to help you check your enrollment status and plan options.

Even in 2025, the consequences of missing your Part B window are the same—financial and medical. So don’t count on updated tools to bail you out; you still need to take action yourself.

Take This Step Seriously to Protect Your Future

Medicare isn’t a one-size-fits-all program. Your work status, employer size, and current health plan all affect whether you need to act now or can afford to wait. But the mistake most people make is assuming they don’t need to do anything—until they get hit with a penalty or denied coverage.

If you’re approaching your 65th birthday, now’s the time to take a close look at your situation. Don’t miss the most overlooked step.

Don’t Let Medicare Penalties Catch You Off Guard

Understanding the Medicare enrollment timeline—especially for Part B—is essential for your healthcare and finances. Whether you’re still working or planning to retire soon, make sure your coverage decisions are intentional and timely. If you’re unsure how your current coverage impacts Medicare enrollment, it’s time to talk with a licensed insurance agent listed on this website who can walk you through your options.