Turning 65 doesn’t mean Medicare automatically starts. Nobody shows up at your door. No coverage kicks in without you doing something. If you’re still working, you may have more flexibility in timing than you think — but the rules for that flexibility are specific, and the mistakes people make when they get them wrong can follow them for life.
Here’s what actually determines whether you need to enroll in Medicare at 65, what you can delay, what you can’t, and which decisions you’ll want to think through carefully before you get there.
The Rule That Changes Everything: How Many People Work at Your Company?
The single most important factor in whether you can delay Medicare is your employer’s size — specifically, whether the company employs 20 or more people.
If your employer has 20 or more employees, your employer’s group health plan is considered “primary” — meaning it pays first, and Medicare would pay second. In this situation, you’re allowed to delay enrolling in Medicare Part B (and Part D) without triggering a late enrollment penalty, as long as you stay on employer coverage. When you eventually retire or lose that coverage, you’ll have a Special Enrollment Period to sign up.
If your employer has fewer than 20 employees, the rules flip. Medicare becomes the primary payer at 65, and your employer plan pays second. If you delay enrolling in Part B in this situation, your employer plan may pay significantly less — because it’s calculating its share assuming Medicare is already covering its portion. You could end up with much higher out-of-pocket costs, and eventually a penalty too. For people at small employers, enrolling in Medicare at 65 is almost always the right move.
This is the rule that catches the most people off guard. Employer size isn’t something most people think to check when they’re planning their Medicare enrollment, but it changes everything.
Part A vs. Part B: These Are Not the Same Decision
Most people in this situation enroll in Part A and delay Part B. Here’s why that makes sense.
Part A — which covers inpatient hospital care, skilled nursing, hospice, and some home health services — is free for most people who’ve paid Medicare taxes long enough. There’s almost no financial reason not to take Part A when you’re first eligible, even if you’re still working. For most people, it doesn’t conflict with employer coverage.
Part B is the piece you can usually delay if you have qualifying employer coverage at a large employer. Part B covers outpatient care, doctor visits, and medical services — and it comes with a monthly premium ($202.90 in 2026). When you have solid employer coverage that pays primary, paying that premium on top doesn’t usually make sense.
Enrolling in Part A when eligible while delaying Part B is a standard and appropriate approach for most people still working at a large employer. But there’s one situation where even Part A becomes a problem — and it involves an HSA.
The HSA Conflict Nobody Warns You About
If you’re contributing to a Health Savings Account (HSA) through a high-deductible health plan, enrolling in any part of Medicare — including premium-free Part A — disqualifies you from making further HSA contributions. Medicare and HSA contributions don’t coexist.
This matters because Part A often auto-enrolls you when you sign up for Social Security benefits. If you claim Social Security before age 65 (or at 65 while still working), Medicare Part A enrollment may be triggered without you realizing it — and your HSA contributions become a problem.
If you’re still contributing to an HSA and plan to continue working past 65, you’ll want to hold off on both Social Security and Medicare enrollment until you’re ready to stop HSA contributions. Many advisors recommend stopping contributions at least six months before your intended Medicare start date, since Part A can be backdated up to six months.
If HSAs are part of your financial strategy, this is worth a specific conversation before you make any enrollment decisions. The rules here are technical enough that getting them wrong can create tax issues — not just Medicare issues.
COBRA Is Not a Qualifying Reason to Delay
This is one of the most expensive mistakes people make in Medicare.
If you leave a job and go onto COBRA — the continuation coverage that lets you stay on your former employer’s plan for up to 18 months — COBRA does NOT count as employer group health coverage for Medicare purposes. It is not considered a valid reason to delay Part B enrollment.
That means if you turn 65 while on COBRA and don’t enroll in Medicare, you’ll be racking up months that count toward a late enrollment penalty — and you won’t have a qualifying Special Enrollment Period when COBRA ends. You’ll be subject to the standard rules, and the penalty will be permanent.
The same applies to retiree health coverage. Coverage through a former employer’s retiree plan is not the same as active employer coverage and generally doesn’t allow you to delay Medicare without penalty. Medicare late enrollment penalties are calculated at 10% of the Part B premium for every 12 months you delayed without valid coverage — and they last for life.
If you’re leaving your job and considering COBRA, the clock for Medicare enrollment is already running.
The 8-Month Window After You Stop Working
When you retire or lose qualifying employer coverage — whichever comes first — you have an 8-month Special Enrollment Period to sign up for Medicare Parts A and B without penalty. This window opens the month after employment ends (or coverage ends, if that happens sooner).
Eight months sounds comfortable. In practice, most advisors recommend not waiting. Medicare Advantage and Medigap plans have their own enrollment timelines and rules that can make late-in-window enrollment messy. Acting within the first month or two after you stop working gives you the most flexibility.
To understand more about when you should sign up for Medicare based on your situation, the enrollment timing rules are worth reviewing before your last day of work — not after.
Why the Medigap Window Matters When You Eventually Retire
Here’s a planning consideration most people don’t think about until it’s relevant: when you enroll in Medicare Part B for the first time, you have a 6-month Medigap open enrollment window. During that window, Medigap insurers cannot deny you coverage or charge you more based on your health history. That guaranteed-issue protection is automatic and time-limited — it doesn’t come back.
For people still working past 65, this window opens the day your Part B starts — which might be when you retire at 68 or 70, not at 65. The good news is that the window is tied to when you first enroll in Part B, not when you turn 65.
But if you’re thinking about eventually having a Medigap plan, it’s worth knowing what your options will look like when that window opens. The comparison between Medicare Advantage vs. Medigap becomes a real decision the moment you retire, and understanding it in advance means you’re not making it under pressure. If you think Medicare Advantage might be the right path, how to compare Medicare Advantage plans gives you the framework for evaluating what’s available in your area.
What About Part D?
If your employer’s prescription drug coverage is considered “creditable” — meaning it’s at least as good as the standard Medicare drug benefit — you can delay Part D enrollment without penalty as well. Your employer is required to notify you each year about whether their coverage meets this standard.
If you delay Part D and your employer coverage is not creditable, or if you have a gap in coverage, you may face a Part D late enrollment penalty when you eventually do sign up. That penalty is also permanent.
For a full breakdown of what Medicare actually covers — including where employer coverage typically overlaps and where gaps appear — that’s worth reviewing as you plan your transition.
For a comprehensive look at all the rules around Medicare while you’re still employed, the full guide to Medicare while working past 65 is a thorough resource for the technical details.
The Bottom Line
Whether you need Medicare at 65 depends on your employer size, your plan type, your HSA situation, and your retirement timeline. For most people at large employers with good coverage, delaying Part B makes sense and is entirely safe — as long as you don’t confuse your situation with COBRA, retiree coverage, or a small employer plan.
The transition from employer coverage to Medicare is one of the most consequential enrollment decisions you’ll make. Getting it right protects your budget and your future coverage options. Getting it wrong can mean lifetime penalties and coverage gaps that are hard to undo.
Brickhouse Can Help You Plan This Transition
If you’re turning 65 soon and still working — or if you’re planning ahead for a retirement date in the next year or two — this is exactly the kind of transition we help people navigate at Brickhouse. We look at your specific situation: your employer size, your current coverage, your HSA, your intended retirement date, and what your Medicare options will look like when you’re ready.
No scripts. No pressure. Just a clear plan for your specific timeline.
Schedule a free consultation with the Brickhouse team and get a straightforward answer for your situation.
FAQs
Q: Do I have to enroll in Medicare when I turn 65 if I’m still working? Not necessarily. If you have employer group health coverage through a company with 20 or more employees, you can delay Medicare Part B enrollment without a penalty. You’ll have an 8-month Special Enrollment Period after you stop working to sign up. However, if your employer has fewer than 20 employees, Medicare becomes the primary payer at 65 and you should enroll to avoid coverage gaps and future penalties.
Q: Can I stay on my employer’s health plan instead of taking Medicare at 65? Yes, if your employer has 20 or more employees. Your employer plan remains primary, and you can delay Medicare Part B without penalty. Most people in this situation still enroll in premium-free Part A since there’s usually no downside — unless you’re contributing to an HSA.
Q: What happens if I’m on COBRA at 65? COBRA is not considered qualifying employer group health coverage for Medicare purposes. If you’re on COBRA when you turn 65 and don’t enroll in Medicare, the months you delay will count toward a late enrollment penalty. COBRA does not give you the right to delay Medicare without penalty.
Q: Can I keep contributing to my HSA if I enroll in Medicare? No. Enrolling in any part of Medicare — including premium-free Part A — disqualifies you from making further contributions to a Health Savings Account. If you want to keep contributing to your HSA, you need to delay Medicare enrollment entirely (both Part A and Part B). This also means delaying Social Security, since Social Security enrollment typically triggers Part A.
Q: How long do I have to sign up for Medicare after I stop working? You have an 8-month Special Enrollment Period starting the month after your employment ends or your employer coverage ends, whichever comes first. Most advisors recommend enrolling in the first month or two of that window to give yourself the most flexibility with Medicare Advantage and Medigap plan options.
Q: Will I face a penalty if I delay Medicare while working? If you have qualifying employer coverage from a large employer (20+ employees) and delay Part B, no penalty applies — as long as you enroll during your Special Enrollment Period when you stop working. If you delay without qualifying coverage, the Part B late enrollment penalty is 10% of the monthly premium for every 12 months you were without coverage, and it’s permanent.
Q: When does my Medigap open enrollment window open if I delayed Medicare? Your 6-month Medigap guaranteed-issue open enrollment window opens when you first enroll in Medicare Part B — not when you turn 65. So if you retire at 68 and enroll in Part B then, your Medigap window opens at 68. The timing is tied to your Part B start date, not your birthday.
