I wrote a while back about Medicare's enrollment periods — AEP, the Advantage OEP, Medigap open enrollment. Those all assume one thing: that you're already on Medicare. This article is for the Nevadans I talk to every month who aren't there yet, because they're still working at 65, still covered by a job-based health plan, and quietly unsure whether Medicare is even something they need to think about right now.
The honest answer is: it depends on a number most people never ask about — how many employees your company has. Get that number wrong, or ignore it, and you can end up with a permanent premium penalty or a real gap in coverage. Get it right, and turning 65 while still working can be completely uneventful.
1. The rule that actually decides it: employer size
Medicare's rules treat a large employer differently than a small one. If your employer — or your spouse's — has 20 or more employees, its group health plan is generally considered primary once you turn 65, and Medicare would pay second if you had both. That means you're allowed to delay Part B with no late penalty for as long as that coverage continues, and simply enroll later when the job or the coverage ends.
If your employer has fewer than 20 employees, the roles usually flip: Medicare becomes primary at 65, and the small employer plan pays second — often paying very little on a claim until Medicare is actually in place. In that situation, most people need to enroll in Medicare on time, the same as if they weren't working at all, or risk a real gap in what actually gets paid.
This single number is why two coworkers who both turn 65 this year, at two different companies, can need two completely different answers. It's worth confirming directly with your employer's HR or benefits department — not assuming based on how the company feels.
2. Why Part A alone is usually still worth taking
Even when Part B can wait, Part A — hospital coverage — is premium-free for most people who've worked and paid Medicare taxes long enough, and it can pay secondary to an employer plan for inpatient stays at no added cost. For that reason, most people at a large employer still enroll in Part A at 65 and simply postpone Part B.
There's one significant exception, and it trips up more Nevadans than any other piece of this: if you or your spouse has a health savings account (HSA) tied to a high-deductible health plan, taking Part A — even alone, even for free — makes you ineligible to keep contributing to that HSA. If you or your employer are still funding it, this is the detail that changes the whole decision.
3. The HSA trap: Part A reaches back six months
Here's the part that catches people who did everything else right. When you eventually enroll in Medicare Part A after 65, your entitlement isn't just effective the month you apply — it can be made retroactive up to six months (never earlier than the month you turned 65). If you were still contributing to an HSA during that retroactive window, the IRS considers those contributions excess, and they need to be corrected.
The practical fix is simple once you know to plan for it: if you intend to keep contributing to an HSA, stop those contributions at least six months before you plan to enroll in Medicare — not six months before you turn 65, but six months before the actual enrollment date, if that's later. This is exactly the kind of detail worth confirming with your benefits administrator and a tax advisor before you sign anything.
4. When you finally stop working: the 8-month window
Whenever active employment or the employer coverage tied to it ends — you retire, you're laid off, the company changes plans — you get an 8-month Special Enrollment Period to sign up for Part B with no late penalty. It starts the month after employment ends or the coverage ends, whichever comes first, and it runs whether you decide to enroll in month one or month eight.
The mistake I see most often here involves COBRA and retiree coverage. Neither one counts as coverage based on current employment, so neither one extends this 8-month clock — it starts the day active employment stops, even if you elect COBRA the very next day and fully intend to use all 18 months of it. Plenty of people discover this only after their COBRA runs out, find themselves well past the 8-month window, and are staring down a late-enrollment penalty and a wait for the next general enrollment period. The fix is planning: know your last active-employment date before it arrives, and start the Medicare paperwork around it, not around when COBRA happens to end.
Getting Part B enrolled during this window also requires proof the prior coverage was creditable — typically a form your employer completes (CMS-L564) submitted alongside your Part B application (CMS-40B) to Social Security. Requesting that form from HR before your last day, rather than after, avoids a scramble later.
5. Where Nevadans get this wrong
Assuming a small employer works like a large one. Carson City, Reno and the Carson Valley have a lot of small businesses and self-employed professionals. If yours has under 20 employees, the "just wait until I retire" instinct is often the exact mistake that creates a claims gap.
Not checking the HSA rule before it's already a problem. This is the one I flag first with almost every client still working past 65 with a high-deductible plan.
Trusting COBRA to buy more time. It buys time to keep seeing your doctors. It does not buy time on the Medicare enrollment clock.
Treating this as separate from the rest of retirement timing. When you stop working touches your Medicare enrollment, your retirement income plan, and eventually the choice I cover in the Medicare Advantage vs. Supplement guide. They're worth planning together, not as four separate fire drills in the same year.
How I'd walk you through it
Three conversations, not a sales pitch.
Conversation one: your employer's size and your HSA status. These two facts alone answer most of "do I need to do anything right now."
Conversation two: your realistic retirement timeline. Even a rough date lets us map the 8-month window and the paperwork before it's urgent.
Conversation three: what comes next. Once Medicare is active, we compare Medicare Advantage and Medicare Supplement against your actual doctors and travel habits — not in the abstract.
Start with my Medicare services page, read more about how I work, or browse the rest of the blog for more plain-English breakdowns.