Do You Need Medicare at 65 If You're Still Working in Missouri?

One of the most common questions I get from working Missourians approaching 65 is simple: do I actually have to sign up for Medicare if I already have insurance through my job? The answer depends on one critical factor — and getting it wrong can cost you thousands of dollars in permanent penalties.

Do You Have to Sign Up for Medicare at 65 If You’re Still Working?

Not necessarily — but it depends entirely on how many employees your employer has. If your employer has 20 or more employees, your employer plan is considered primary coverage and Medicare is secondary. You can delay Medicare Part B enrollment without penalty while you remain actively employed and covered by that plan.

If your employer has fewer than 20 employees, Medicare becomes primary at 65 regardless of whether you’re still working. In that situation you must enroll in Medicare to avoid both coverage gaps and the permanent late enrollment penalty.

This single rule — the 20-employee threshold — is the most misunderstood regulation in Medicare. I’ve worked with Missouri clients who delayed enrollment assuming their employer coverage protected them, only to discover they’d been accruing penalties for years.

What Is the 20-Employee Rule for Medicare?

The 20-employee rule determines whether your employer plan or Medicare pays first when you have both. Under the Medicare Secondary Payer rules, employers with 20 or more employees must offer active employees and their spouses the same health coverage at 65 that they offer younger employees. Your employer plan remains primary and Medicare is secondary — meaning Medicare only picks up costs after your employer plan has paid.

For employers with fewer than 20 employees, the rules flip. Medicare becomes primary at 65, and your employer plan becomes secondary. If you haven’t enrolled in Medicare, your employer plan may refuse to pay claims it would normally cover — leaving you with unexpected bills and no recourse.

The threshold is based on the number of employees during 20 or more calendar weeks in the current or preceding year. If your employer fluctuates near the 20-employee mark, this is worth verifying directly with your HR department — and confirming in writing.

What Happens If You Don’t Enroll in Medicare at 65 With a Small Employer?

If your employer has fewer than 20 employees and you don’t enroll in Medicare at 65, two things happen. First, your employer plan may pay as if Medicare is primary — meaning they only cover what Medicare would have left unpaid. Since Medicare hasn’t paid anything, your employer plan calculates your benefit as if it had, resulting in significantly reduced payments and large unexpected bills for you.

Second, when you eventually do enroll in Medicare, you’ll face the permanent Part B late enrollment penalty — 10% of the standard premium for every 12-month period you delayed without qualifying coverage. In 2026, the standard Part B premium is $202.90 per month. A three-year delay adds approximately $60 per month permanently — every month for the rest of your life.

I’ve sat across the table from Missouri clients who owed this penalty for 5, 8, even 12 years before anyone caught the mistake. The financial damage is real and irreversible.

Should You Enroll in Medicare Part A at 65 Even If You’re Still Working?

Most people should enroll in Medicare Part A at 65 even while still working, because Part A is premium-free for anyone who has worked at least 40 quarters and paid Medicare taxes. There’s typically no reason to delay free coverage.

The exception: if you’re contributing to a Health Savings Account (HSA). Enrolling in Medicare Part A — even premium-free Part A — makes you ineligible to contribute to an HSA going forward. If you have a high-deductible health plan paired with an HSA and want to keep contributing, you may want to delay both Part A and Part B until you stop working.

Additionally, be aware that Social Security automatically enrolls you in both Part A and Part B when you begin collecting Social Security benefits. If you’re still working and don’t want Part B yet, you must actively decline it — and understand the rules before doing so.

What About Medicare Part B If You’re Still Working?

Part B is where the decision gets more complex. Part B covers outpatient services — doctor visits, preventive care, lab work, outpatient procedures. The 2026 Part B premium is $202.90 per month, and it’s deducted from your Social Security check if you’re collecting, or billed quarterly if you’re not.

If your employer has 20 or more employees and you have solid employer coverage, delaying Part B enrollment is often the right financial decision. You’ll use your Special Enrollment Period — a protected 8-month window after your employer coverage ends — to sign up without penalty when you retire.

If your employer has fewer than 20 employees, enroll in Part B at 65. No exceptions.

How Does Medicare Work With Missouri Employer Coverage After Retirement?

When you retire, your employer coverage typically ends — either immediately or after a COBRA continuation period. This triggers your Special Enrollment Period for Medicare, giving you 8 months to enroll in Part B without penalty.

One critical mistake I see repeatedly: Missouri retirees who elect COBRA after leaving their job assume COBRA counts as creditable coverage that extends their Special Enrollment Period. It does not. COBRA is not creditable coverage for Medicare purposes. Your 8-month Special Enrollment Period clock starts when your active employer coverage ends — not when your COBRA coverage ends.

This is one of the most expensive Medicare mistakes I see in my Kansas City metro practice. A client leaves their job, elects COBRA for 18 months, then tries to enroll in Medicare — only to discover their Special Enrollment Period ended 10 months ago. The result is a permanent penalty and a gap in coverage waiting for the General Enrollment Period.

What Should Missouri Workers Do 6 Months Before Turning 65?

Six months before your 65th birthday is the right time to start the Medicare planning process — regardless of whether you plan to enroll immediately. Here’s what I recommend for working Missourians in the Kansas City area:

First, verify your employer’s size. Ask HR directly: does the company have 20 or more employees? Get confirmation in writing if possible. This single data point determines your entire Medicare strategy.

Second, understand your current coverage costs. Many working Missourians are surprised to discover that Medicare plus a Medigap Plan G costs less per month than their employer’s premium contribution. Even if you’re not required to enroll at 65, you may want to — especially if your employer coverage is expensive or your employer has announced plan changes.

Third, identify your HSA situation. If you’re contributing to an HSA, understand the enrollment rules before your birthday. Stopping HSA contributions 6 months before Part A enrollment begins is required to avoid tax penalties due to Medicare’s retroactive coverage rules.

Fourth, schedule a consultation with an independent Medicare advisor. I work with working Missourians in Blue Springs, Lee’s Summit, Independence, and throughout the KC metro to review exactly these questions — at no cost.

Does Employer Coverage Count as Creditable Coverage for Medicare?

Active employer coverage from a current employer with 20 or more employees counts as creditable coverage for Medicare Part B, allowing you to delay enrollment without penalty. It also counts as creditable coverage for Part D drug coverage, meaning you can delay a drug plan without the Part D late enrollment penalty while covered.

Retiree coverage — insurance provided by a former employer after you stop working — does not typically protect you from the Part B late enrollment penalty. Retiree coverage is secondary to Medicare, and delaying Medicare enrollment while on retiree coverage can still trigger penalties. This is another area where the rules are routinely misunderstood.

What Are the Medicare Rules for Missouri State and Federal Employees?

Missouri state employees and federal employees turning 65 face the same 20-employee threshold rules as private sector employees — the employer plan is primary as long as you’re actively employed. Federal employees covered by the Federal Employees Health Benefits Program can generally delay Medicare Part B while working, as FEHB plans are large-employer plans by definition.

Missouri teachers and school district employees should verify their district’s size and plan structure. Many Missouri school districts have 20 or more employees and offer coverage that qualifies for delayed Medicare enrollment, but confirmation from your benefits administrator is essential before making any decision.

Can Your Employer Require You to Enroll in Medicare at 65?

No. Employers with 20 or more employees cannot require employees to enroll in Medicare at 65, cannot offer financial incentives to encourage Medicare enrollment, and cannot cancel or reduce your employer coverage simply because you’ve reached Medicare eligibility age. These protections are part of the Medicare Secondary Payer rules enforced by the Centers for Medicare & Medicaid Services.

If your employer pressures you to drop employer coverage and switch to Medicare at 65, this may be a violation of federal law. Contact your State Health Insurance Assistance Program — in Missouri, that’s the SHIP program (formerly CLAIM) at 1-800-390-3330 — or consult with an independent Medicare advisor before making any changes.

Frequently Asked Questions

Do I have to sign up for Medicare at 65 if I have insurance through my spouse’s employer?

It depends on your spouse’s employer size. If your spouse’s employer has 20 or more employees and you’re covered as a dependent on that plan, you can delay Medicare enrollment without penalty. If the employer has fewer than 20 employees, Medicare becomes primary for you at 65 regardless of whose employer provides the coverage.

What is the Special Enrollment Period for Medicare after leaving a job?

The Special Enrollment Period is an 8-month window that begins the month after your active employer coverage ends — or the month after you stop working, whichever comes first. During this period you can enroll in Medicare Part B without the late enrollment penalty. Note that the SEP begins when active coverage ends, not when COBRA ends.

Can I keep my HSA if I enroll in Medicare?

Once you enroll in any part of Medicare — including premium-free Part A — you can no longer contribute to a Health Savings Account. You can still use existing HSA funds to pay Medicare premiums and out-of-pocket costs. If you want to continue HSA contributions, you must delay all Medicare enrollment, including Part A.

What if my employer has exactly 20 employees?

The 20-employee threshold applies to employers with 20 or more employees during 20 or more calendar weeks in the current or preceding calendar year. An employer with exactly 20 employees meets the threshold. If your employer’s headcount fluctuates, ask HR to confirm the company’s status in writing before making Medicare decisions.

How do I verify my employer’s size for Medicare purposes?

Ask your HR department directly. The question is: does the company have 20 or more employees for Medicare Secondary Payer purposes? Request written confirmation. Your Medicare decisions carry permanent financial consequences, so verbal assurances are not sufficient.