Working Past 65: When to Enroll in Medicare (and When to Delay)

If you are still working at 65 and covered by a group health plan through a large employer, you can usually delay Medicare Part B and Part D without a penalty and enroll later during a Special Enrollment Period. That is the short answer. The longer answer depends on the size of your employer, whether you contribute to a Health Savings Account, whether your spouse is on your plan, and whether you are drawing Social Security. Get any one of those details wrong and you can end up with a lifetime penalty, a coverage gap, or a big HSA tax surprise.

This is one of the most common calls I get. Someone is 64, still working, planning to work until 68 or 70, and their HR team gave them a one-liner that did not actually answer the question. Here is the honest, plain-English breakdown of what to do at 65 if you are still working, what to do when you actually retire, and the specific mistakes that quietly cost people money for the rest of their lives.

Do You Have to Enroll in Medicare at 65?

No. Medicare enrollment is voluntary. Nothing forces you to sign up at 65. But the rules around what happens when you delay are strict, and skipping the wrong part at the wrong time creates penalties that follow you for the rest of your life.

The rule that matters most is this: if you or your spouse are actively working and covered by a group health plan through an employer with 20 or more employees, you can delay Part B (medical) and Part D (drugs) without penalty. When you eventually leave that coverage, you get a Special Enrollment Period to sign up.

If any part of that sentence is not true for you, the answer changes. Smaller employer, retiree coverage, COBRA, marketplace plan, VA, TRICARE. Each one has its own rules and its own trapdoors. We will walk through the common ones below.

When You Should Delay Medicare

Delaying Part B and Part D usually makes sense in these situations:

1. You work for a company with 20 or more employees and you are on the group health plan. Your group plan stays primary. You are not required to enroll in Part B, and you get a Special Enrollment Period whenever you eventually leave the plan.
2. Your spouse works for a large employer and you are on their plan as a dependent. Same rule. The active-employee coverage is primary and you can delay Part B without penalty.
3. You contribute to a Health Savings Account and want to keep contributing. Enrolling in ANY part of Medicare, including free Part A, ends new HSA contributions. If you want to keep funding the HSA, you have to delay all of Medicare, not just Part B.
4. Your employer plan is genuinely good. Some group plans have lower premiums and better networks than what Medicare + a Supplement would cost you. If the math on your specific plan says stay, stay.

When You Should NOT Delay Medicare

Delaying Part B is a mistake in these situations, and this is where I see people get burned:

1. Your employer has fewer than 20 employees. Medicare becomes PRIMARY at 65 for these small groups. If you skip Part B thinking your group plan will cover you, your group plan will pay as if Medicare paid first, and most of your medical bills will go unpaid. This is the single most expensive mistake I see. Verify your employer size with HR in writing.
2. You are on retiree coverage, not active-employee coverage. Retiree plans are considered secondary to Medicare. They do not qualify for the delay. You need Part B on the day you turn 65 or your retiree plan may not pay claims correctly.
3. You are on COBRA. COBRA does not qualify as active-employee coverage. If you turn 65 while on COBRA, you need to enroll in Medicare on time. COBRA does not give you a Special Enrollment Period when it ends.
4. You are on a marketplace (ACA) plan. Marketplace subsidies end when you become eligible for Medicare. Staying on a marketplace plan past 65 usually costs you more than Medicare would and does not give you an SEP later.
5. You are drawing Social Security. If you are already collecting Social Security when you turn 65, you are automatically enrolled in Part A and Part B. You can decline Part B, but that adds paperwork. Most people who are drawing Social Security should just accept the enrollment.

Should You Sign Up for Part A While Still Working?

Part A covers hospital stays and is premium free for anyone who worked at least 10 years (40 quarters) paying Medicare taxes. Since it does not cost you anything, most people should enroll in Part A at 65 even if they are still working. It becomes a secondary layer of hospital coverage behind your group plan and can pick up costs your employer plan does not cover.

There is one big exception: Health Savings Accounts. Enrolling in Part A, even by itself, disqualifies you from contributing new money to an HSA. Existing balance is fine and you can keep using it, but no new contributions.

If you are still funding an HSA and want to keep doing that, you need to actively delay Part A too. That means not filing for Social Security either, because Social Security enrollment automatically enrolls you in Part A. And Part A backdates up to 6 months when you sign up, which can turn HSA contributions from those 6 months into excess contributions you have to pull back out. The rules are strict, so if HSA is in play, plan the timing carefully.

The Special Enrollment Period When You Finally Retire

When you leave your job or your employer coverage ends, you get a Special Enrollment Period (SEP) to sign up for Medicare Part B without penalty. Here is exactly how it works:

• The window is 8 months starting the month after your employment ends OR the month after your group coverage ends, whichever happens first.
• You need forms CMS-40B and CMS-L564 to enroll during the SEP. CMS-L564 is completed by your employer and confirms you had continuous group coverage since 65. Get that form signed before you leave the job. Chasing down a former HR contact 6 months later is painful.
• Part D has its own separate window of 63 days from the date you lose creditable drug coverage. Miss it and you can owe a Part D late enrollment penalty even though you signed up for Part B on time.
• Medicare Supplement plans have their own separate 6-month guaranteed-issue window that starts when your Part B becomes effective. Miss that window and you can be denied a Medicare Supplement based on health, or charged more.

Practical tip: start the Medicare enrollment paperwork about 3 months before you actually retire. That gives you time to file everything and have coverage in place the day your group plan ends. There is no gap. Wait until the day after your last paycheck and you may go a month or two without full coverage.

The HSA Trap (Read This If You Have One)

Health Savings Accounts are one of the best tax vehicles in the tax code, and they are also the number one reason someone in their 60s should think carefully about Medicare timing. Here are the two traps:

1. Filing for Social Security auto-enrolls you in Part A. If you sign up for Social Security at 66, you are automatically enrolled in Part A whether you asked for it or not. That immediately ends new HSA contributions.
2. Part A backdates up to 6 months. When you eventually enroll in Part A, the effective date can be up to 6 months before you signed up (but not earlier than your 65th birthday). Any HSA contributions you made during those 6 backdated months become excess contributions, which are taxable and can carry a 6 percent excise tax if you do not withdraw them by the tax deadline.

If you want to keep contributing to your HSA past 65, the safest move is to stop HSA contributions 6 months before you file for Social Security or Medicare. That is the rule most CPAs and HSA custodians will walk you through, and it protects you from the backdating problem.

A Real-Life Example

Meet John. He turns 65 in October. He works for a company with 400 employees, is on the company health plan, contributes to an HSA, and plans to work until 68. His wife Debbie is 62 and on his health plan.

Here is what John should do:

• Delay Part B. His group plan is primary and he has an SEP when he eventually retires.
• Delay Part A too, because he wants to keep contributing to his HSA. That means not filing for Social Security yet either.
• Delay Part D. His employer drug plan is creditable coverage. Confirm it in writing every year (his plan sends a Notice of Creditable Coverage).
• About 3 months before retirement at 68, start the Medicare enrollment paperwork. Get CMS-L564 signed by HR while he is still on the payroll.
• Stop HSA contributions 6 months before he plans to file for Medicare or Social Security to avoid the Part A backdating problem.
• Debbie stays on his group plan until he retires, then goes on the marketplace until she turns 65 (or COBRA, whichever costs less).

That plan protects the HSA, avoids the Part B penalty, keeps Debbie insured, and lands John on Medicare cleanly the month after he retires. Total penalty exposure: zero.

Common Mistakes That Cost People Money

I see the same five mistakes on almost every call from someone working past 65:

• Assuming a small employer plan is enough. Under 20 employees, Medicare is primary. Skipping Part B leaves most claims unpaid.
• Contributing to an HSA after filing for Social Security. Filing for Social Security auto-enrolls you in Part A, which ends HSA contributions and can backdate up to 6 months.
• Missing the Special Enrollment Period after retirement. The 8-month window sounds long, but a month or two passes fast when you are moving houses, dealing with a spouse's plan, or traveling.
• Not getting CMS-L564 signed before leaving the employer. That form has to come from HR. Chasing it down after you are no longer an employee is painful and slow.
• Missing the 6-month Medicare Supplement window. Medicare Supplement guaranteed issue only lasts 6 months from Part B effective date. Miss it and you can be denied coverage or charged more based on your health.

How to Enroll When the Time Comes

1. Confirm your employer size and coverage type in writing. Get HR to tell you (a) how many employees the company has, (b) whether your plan is creditable coverage for drug purposes, and (c) exactly when your coverage ends after you retire.
2. Fill out CMS-40B (Part B application) and CMS-L564 (employer certification). Both are available on Medicare.gov. HR fills out CMS-L564. You submit both to Social Security.
3. Submit paperwork 2 to 3 months before your target Part B start date. This gives Social Security time to process and put coverage in place without a gap.
4. Pick a Part D plan or Medicare Advantage or Medicare Supplement. Do this in parallel. Do not wait until Part B is effective, because the plans have their own 63-day windows.
5. Check for a Medicare Supplement guaranteed-issue window. A good agent runs pricing on every Supplement plan in your area and picks the plan that fits your budget and health situation, then locks it in during your guaranteed-issue window.

Frequently Asked Questions