The employer question
Working past 65: the answer hinges on one number
Short answer: if your health coverage comes from your own or your spouse’s current employment at an employer with 20 or more employees, you can delay Medicare Part B penalty-free and enroll within 8 months of that coverage ending. Under 20 employees, Medicare becomes primary at 65 and you must enroll on time. Everything else on this page is the fine print around that one number.
Key takeaways
- At 20+ employees, employer coverage stays primary: you may delay Part B penalty-free and get an 8-month Special Enrollment Period when work ends.
- Under 20 employees, Medicare is primary at 65 whether you enrolled or not; enroll on time or claims can go unpaid.
- COBRA and retiree coverage don’t count as current employment and don’t protect you from penalties.
- HSA contributors: enrolling in any part of Medicare, even free Part A, ends contribution eligibility, and Part A can backdate 6 months.
- When you eventually retire, your 6-month Medigap window starts fresh with your delayed Part B.
The rule that decides everything
Medicare’s coordination rules turn on employer size. At 20 or more employees, the group health plan pays first and Medicare (if you have it) pays second, so skipping Part B costs you nothing in coverage. Under 20, the order flips: Medicare pays first at 65, and the employer plan is only responsible for what’s left, whether or not you actually enrolled. That flip is why the same decision ("I’ll just keep my work insurance") is perfectly safe at a 500-person company and quietly dangerous at a 15-person one.
If your employer has 20+ employees
- You may delay Part B with no late penalty for as long as the employment and coverage continue.
- Most people still take Part A at 65, since it’s premium-free and sits quietly behind the employer plan, with one big exception below.
- Compare anyway. Some employer plans have premiums and deductibles that make full Medicare (Part B plus Medigap plus Part D) competitive. Delaying is a right, not an obligation.
- Confirm creditable drug coverage. Your benefits office must tell you annually whether the plan’s drug coverage is "creditable" for Part D; keep those notices, they’re your penalty shield later.
If your employer has fewer than 20
Enroll in A and B during your normal 7-month window, full stop. The employer plan becomes secondary at 65, and small-group insurers can and do deny the share Medicare "should" have paid when someone skips enrollment. People discover this at claim time, which is the most expensive possible classroom. Your employer plan may still be worth keeping as secondary coverage; that’s a benefits-office conversation, but it happens alongside Medicare, not instead of it.
The three traps that fill the forums
| Trap | The wrong assumption | The rule |
|---|---|---|
| The COBRA myth | "I have 18 months of COBRA, so I can wait" | COBRA isn’t current employment; the Part B penalty clock (10% per 12 months, permanent) runs anyway |
| The HSA collision | "Part A is free, might as well take it" | Any Medicare enrollment ends HSA eligibility, and Part A can backdate up to 6 months into past contributions |
| The HR guess | "HR thinks we’re big enough" | The 20-employee count follows Medicare’s definition; get it, and the active-employment confirmation, in writing |
Coordination and penalty rules per Medicare.gov and SSA; the employee count uses Medicare’s counting rules, not headcount folklore.
The HSA case deserves one more sentence: if you’re contributing and want to keep contributing, delay all of Medicare, including Part A, and stop contributions roughly six months before you eventually enroll, because of the backdating. Also know that claiming Social Security triggers automatic Part A, which forces the issue.
The exit sequence, when retirement finally comes
- Your 8-month Special Enrollment Period opens when the employment or the coverage ends, whichever comes first. Enroll in Part B early in it; don’t ride the deadline.
- Your 6-month Medigap window starts fresh with the new Part B effective date, guaranteed-issue pricing included. Delayers don’t lose this; it just waits.
- Line up drug coverage within 63 days of losing creditable employer drug coverage to keep the Part D penalty at zero.
- Sequence it gap-free: Part B effective date, Medigap effective date, and Part D effective date on the same day the employer coverage ends is the clean version.
And the standing warning: retiree health benefits offered as a bridge are welcome money, but they follow the COBRA logic, not the current-employment logic. The 8-month clock runs from when work ends.
Working spouse, covered spouse
The rule extends to spousal coverage: if you’re 65 and covered under your spouse’s current employment at a 20+ employer, you can delay Part B on the same terms. The moment that employment ends (or the spouse retires), your own 8-month clock starts. The reverse situation, where the younger spouse depends on your coverage when you move to Medicare, is its own planning problem, covered in the younger-spouse article.
Questions people also ask
Do I have to sign up for Medicare at 65 if I’m still working?
Does COBRA let me delay Medicare?
Can I keep contributing to my HSA after 65?
What happens when I retire after delaying Medicare?
Should I take Part A while working even if I delay Part B?
Sources for this article
- SSA.govSign up for Medicare: enrollment mechanics, Special Enrollment Periods, and automatic-enrollment triggers.
- Medicare.govMedicare.gov: coordination-of-benefits rules for employer coverage.
- Medicare.govBuying a Medigap policy: how the 6-month window resets with delayed Part B.
Figures checked against these sources in July 2026. We update within weeks when CMS publishes new amounts.