Medicare While Still Working: When to Enroll and When to Wait

One of the most common — and most consequential — questions I get from people approaching 65 is some version of this: "I'm still working and I have good coverage through my employer. Do I have to sign up for Medicare?"

The answer is: it depends. And the stakes are high enough that getting it wrong can result in a lifelong penalty on your Medicare premiums or a coverage gap you did not see coming.

Here is what you actually need to know.

The 20-Employee Rule: The Key Variable

Whether you can safely delay Medicare enrollment depends almost entirely on how many people your employer has on payroll.

If your employer has 20 or more employees: Your employer plan is the primary payer, and Medicare is secondary. You can delay enrolling in Medicare Part B (and Part D) without penalty, as long as you have continuous coverage under your employer's group plan. When you eventually leave that coverage — whether because you retire or your employer coverage ends — you get a Special Enrollment Period (SEP) to sign up for Medicare without penalty.

If your employer has fewer than 20 employees: Medicare becomes the primary payer, even if you are still actively employed. In this case, delaying Medicare Part B is risky, because your employer plan may pay little or nothing for services that Medicare would have covered. You should generally enroll in Part B during your Initial Enrollment Period (IEP) regardless of your employer coverage.

Do Not Skip Part A (Usually)

Most people who are eligible for premium-free Medicare Part A (based on their own or a spouse's work history) should enroll in Part A at 65, even if they are keeping employer coverage.

Part A is free for most people, and it can act as a secondary payer for hospital costs. The main exception: if you are contributing to a Health Savings Account (HSA), enrolling in any part of Medicare makes you ineligible to continue contributing to your HSA. In that case, you may choose to delay Part A as well — but stop HSA contributions at least six months before you plan to enroll, because Medicare enrollment is sometimes backdated up to six months.

The Part B Decision: Primary vs. Secondary

Part B has a standard premium of $185.00 per month in 2026 (more if your income is above certain thresholds). Many people want to delay paying that premium if their employer plan already covers doctor visits and outpatient care.

This is fine — as long as you qualify under the 20-employee rule and you sign up when your employer coverage ends. The trap that catches people is not enrolling on time when that employer coverage ends.

You have 8 months from the date your employer coverage ends to enroll in Part B without a late enrollment penalty. This SEP is not triggered by your last day of work — it is triggered by the last day your group health coverage is active. Those are often different dates (COBRA, for instance, does not count as employer-sponsored coverage for this purpose).

Miss that 8-month window, and you face a 10% permanent premium surcharge for every 12-month period you were without Part B coverage when you were supposed to have it.

What About Part D (Prescription Drug Coverage)?

Similar rules apply. If your employer plan includes creditable drug coverage — meaning it is at least as comprehensive as Medicare's standard benefit — you can delay Part D enrollment without penalty.

Your HR department or plan administrator should provide a "creditable coverage" notice each year. If your coverage is creditable, keep it. If it is not, you should enroll in Part D to avoid the late enrollment penalty, which is 1% of the national base premium per month of uncovered gap — permanently.

COBRA: A Common Trap

Many people leave their job and choose COBRA to maintain their employer plan for 18–36 months. COBRA is not considered active employer-sponsored coverage for Medicare purposes. It does not protect you from the late enrollment penalty.

The moment your active employer coverage ends and you switch to COBRA, your Medicare Special Enrollment Period clock starts. You have 8 months to enroll in Part B. If you spend your entire COBRA period assuming you are protected, you may find you missed the window entirely.

If You Are on a Spouse's Employer Plan

The 20-employee rule applies to your spouse's employer if that is the source of your health coverage. As long as your spouse is still actively employed and their employer has 20 or more workers, your coverage is considered active employer-sponsored coverage — and you can delay Medicare enrollment without penalty.

What to Do When You Are Approaching 65 and Still Working

1. Check your employer's size — confirm whether the 20-employee threshold applies.
2. Enroll in Part A unless you are contributing to an HSA and choose to delay.
3. Get written confirmation that your employer plan's drug coverage is creditable — keep this letter for your records.
4. Set a reminder for your last day of employer coverage, not your last day of work. The SEP clock starts then.
5. Do not rely on COBRA as a substitute for enrolling in Medicare on time.
6. Talk to a licensed advisor before making any decision if you are unsure — especially if you are within a few months of your IEP or a coverage change.

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If you are approaching 65 with employer coverage or planning to retire soon, let's make sure your timing is right. Schedule a consultation — I help beneficiaries across Florida, Alabama, Georgia, and North Carolina navigate these decisions every day.

This article provides general educational information. Individual Medicare rules and timelines depend on your specific situation. Always verify current rules with a licensed Medicare advisor or Medicare.gov.

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Frequently Asked Questions#

Can I keep my employer insurance and Medicare at the same time? Yes. Many people have both. How they coordinate depends on which is the primary payer, which is determined by the size of your employer. Medicare and employer coverage can work together to reduce your out-of-pocket costs.

What happens if I miss my Medicare Special Enrollment Period? If you miss your 8-month SEP after employer coverage ends, you must wait for the General Enrollment Period (January 1 – March 31 each year), and your coverage will not start until July 1. You will also face a late enrollment penalty on your Part B premium — permanently.

Does Medicare coordinate with my employer's HSA? Enrolling in any part of Medicare makes you ineligible to make new contributions to an HSA. If you plan to keep contributing to your HSA past age 65, you need to delay all Medicare enrollment. Plan the timing carefully.

How do I prove I had creditable coverage when I enroll in Part D late? Keep the annual creditable coverage notice from your employer or insurer. When you enroll in Part D, you may need to submit proof of creditable coverage to avoid the penalty. Without documentation, the penalty can be applied.