Transitioning off employer or retiree group coverage and onto Medicare is one of the more confusing moves in the entire process — mostly because the timing rules depend on details specific to your situation. Here’s how to think through it.
First: Are You Retiring, or Just Turning 65 While Still Working?
These are two different situations with different timing considerations.
If You’re Turning 65 and Still Working
The key question is: how many employees does your employer have?
- 20 or more employees: Your group health plan is generally considered “primary,” meaning it pays first. Many people in this situation choose to delay Part B (and sometimes Part A, depending on whether they have an HSA) without penalty until the employer coverage ends. When it does end, you get an 8-month Special Enrollment Period to sign up for Medicare without a late penalty.
- Fewer than 20 employees: Medicare generally becomes primary at 65, which usually means you need to enroll in Parts A and B on time — delaying can create coverage gaps, since your employer plan may pay only after Medicare would have, whether or not you’re enrolled.
A note on Health Savings Accounts (HSAs): if you or your employer are contributing to an HSA, enrolling in any part of Medicare — even just premium-free Part A — makes you ineligible to contribute further. This trips people up because Part A enrollment can sometimes happen automatically if you’re collecting Social Security. Worth checking on before you assume you can keep contributing.
If You’re Retiring
Retiree coverage — whether from a former employer or COBRA — is generally not considered active employer coverage for Medicare purposes, even if it looks similar to what you had while working. That means:
- Retiree coverage and COBRA typically do not give you a Special Enrollment Period the way active employer coverage does
- You generally need to enroll in Medicare during your Initial Enrollment Period, or you could face penalties and coverage gaps
- Many retiree and COBRA plans are designed to work alongside Medicare, not instead of it, once you’re eligible
If your retirement coverage stops before you’re 65, you’ll likely need Marketplace coverage to bridge the gap until Medicare eligibility.
Making the Actual Switch: A General Sequence
- Confirm your enrollment window and whether you qualify for a Special Enrollment Period based on your specific coverage type.
- Enroll in Medicare Parts A and B through Social Security, timed so there’s no gap in coverage.
- Decide your path — Original Medicare plus Medigap and Part D, or a Medicare Advantage plan — ideally researched before your employer coverage ends, not after.
- Time the end of your employer coverage carefully. Coordinate the exact end date with your new Medicare coverage’s start date to avoid any gap.
- Notify your employer’s benefits department of your Medicare enrollment, since some coordination of benefits paperwork may be needed on their end too.
Common Pitfalls in This Transition
- Assuming COBRA counts as “active” coverage for Medicare timing purposes — it generally doesn’t, and this is one of the most common costly mistakes in this transition.
- Waiting until coverage has already ended to start researching Medicare options, leaving no time to compare plans thoughtfully.
- Missing the Medigap Open Enrollment window, which starts the month you’re 65+ and enrolled in Part B — not whenever your employer coverage happens to end.
- Not checking whether your current doctors and medications will be covered under whatever Medicare path you choose, since your employer plan’s network doesn’t carry over.
The Bottom Line
There’s no single “right” timeline here — it depends on your employer’s size, whether you’re retiring or continuing to work, whether an HSA is involved, and what your spouse’s situation looks like too. The rules genuinely change based on these specifics, which is exactly why this transition is worth mapping out with someone before you give notice on your current coverage.
This article is educational and general in nature and is not a substitute for personalized guidance from Medicare, Social Security, or your employer’s benefits administrator. We do not offer every plan available in your area; please contact Medicare.gov or 1-800-MEDICARE for information on all of your options.
Navigating a transition off employer coverage? Schedule a free, no-pressure consultation and we’ll help you map the timeline so nothing falls through the cracks.
