Updated July 2026 · Reviewed by the CoverageCo team
If you have creditable coverage through active employment — yours or a spouse's — you can often delay Part B penalty-free and enroll later through a Special Enrollment Period. If you don't, delaying can mean a permanent premium penalty and a coverage gap. Employer size changes the answer.
Key takeaways
- Coverage from active employment can let you delay Part B. COBRA, retiree, and Marketplace plans generally cannot.
- At smaller employers Medicare often pays first — skipping Part B there can leave claims unpaid.
- You cannot contribute to an HSA once enrolled in any part of Medicare, including premium-free Part A.
- Get written confirmation from your benefits administrator that your coverage is creditable, and keep it.
The short answer
If you have creditable coverage through active employment — yours or your spouse's — you may be able to delay Part B penalty-free and enroll later through a Special Enrollment Period.
If you don't, delaying can cost you a permanent premium penalty and leave you with a gap in coverage.
Everything depends on what kind of coverage you actually have, and that's more specific than most people expect.
Employer size changes the answer
This is the detail that decides most cases, and it's the one people miss.
At larger employers, the group plan generally pays first and Medicare pays second. In that arrangement, delaying Part B is often reasonable.
At smaller employers, Medicare generally pays first and the group plan pays second. If you skip Part B in that situation, you can end up with the primary payer missing entirely — meaning claims your group plan expected Medicare to cover may go unpaid. People have been left with very large bills this way.
The exact employee thresholds are set by federal rules and differ for disability-based eligibility. Confirm your specific situation rather than assuming.
Coverage that does NOT protect you
This trips up a lot of people, because these all feel like real insurance:
- COBRA. It's continuation coverage, not active employment coverage. It generally does not let you delay Part B penalty-free.
- Retiree coverage from a former employer. Same problem — the employment isn't active.
- Marketplace / ACA plans. Once you're Medicare-eligible, these generally don't protect you from the Part B penalty.
- Severance-based coverage. Usually treated like retiree coverage, not active coverage.
The HSA rule that catches people off guard
If you contribute to a Health Savings Account, this matters and the timing is unforgiving.
You cannot contribute to an HSA while enrolled in any part of Medicare, including premium-free Part A. You can still spend what's already in the account, but new contributions have to stop.
There's an additional wrinkle: when you enroll in Medicare after 65, Part A coverage can be made retroactive by several months. If you contributed to your HSA during those retroactive months, those contributions can become excess and taxable. Anyone planning to keep contributing to an HSA past 65 should stop contributions well before enrolling — and talk to a tax professional about the specific timing.
What to do before your 65th birthday
Give yourself a few months of runway and work through this in order:
- Ask your benefits administrator, in writing, whether your plan is creditable coverage for Medicare Part B and Part D.
- Confirm how your employer's plan coordinates with Medicare, and whether it pays primary or secondary.
- Compare what you pay now against what Medicare plus a supplement or Advantage plan would cost. Group coverage isn't automatically the better deal — for some people, especially those paying for family coverage, Medicare comes out ahead.
- If you're contributing to an HSA, decide when contributions stop.
- Whatever you conclude, keep the documentation. You may need it to prove creditable coverage later.
When you eventually retire
Leaving employer coverage opens a Special Enrollment Period for Part B, and it isn't open-ended. Missing it puts you back into general enrollment with delayed coverage and possible penalties.
Start the conversation before your last day, not after. Coordinating a retirement date with a Medicare start date is straightforward when planned and genuinely painful when rushed.
A licensed agent can map this out with you at no cost, including whether staying on your employer plan actually makes financial sense.
Common questions
Can I keep my employer insurance instead of Medicare at 65?
Often yes, if the coverage comes from active employment at a large enough employer. Many people enroll in premium-free Part A and delay Part B. Whether that's the best financial choice depends on what your employer plan costs you compared to Medicare options.
Does COBRA count as creditable coverage for Medicare?
Generally no. COBRA is continuation coverage rather than active employment coverage, so it typically does not let you delay Part B without a penalty. This is one of the most common and costly Medicare misunderstandings.
Can I contribute to my HSA after enrolling in Medicare?
No. Once you're enrolled in any part of Medicare, including premium-free Part A, you can no longer contribute to an HSA. You can still spend existing funds. Because Part A can be applied retroactively, stop contributions well before you enroll and consult a tax professional.
What happens to my Medicare options when I retire?
Losing coverage from active employment opens a Special Enrollment Period, letting you enroll in Part B without a late penalty. The window is limited, so it's best to plan your enrollment alongside your retirement date.