If you're still working at 65, your employer's size determines everything about how Medicare interacts with your job-based coverage. For employers with 20+ employees, your employer plan is primary and you can safely delay Medicare Part B. For employers with fewer than 20 employees, Medicare is primary, and failing to enroll at 65 triggers a 10% Part B penalty per year of delay that lasts for life. According to the Bureau of Labor Statistics, about 20% of Americans 65 and older are still in the workforce.
This guide covers the exact rules for every scenario, large employers, small employers, self-employed, spouses on employer plans, HSAs, COBRA, and the critical deadlines you cannot miss.
How Does Employer Size Affect Your Medicare Decision?
This is the single most important factor. Get it wrong and the penalty is permanent.
| Employer Size | Which Insurance Is Primary | What to Do at 65 | Part B Penalty Risk |
|---|---|---|---|
| 20+ employees | Employer plan is primary | Enroll in Part A (free). You can delay Part B without penalty. | No penalty, employer coverage counts as creditable |
| Fewer than 20 | Medicare is primary | Enroll in Parts A AND B at 65. Medicare pays first; employer plan is secondary. | 10% penalty per year of delay, permanent |
| Self-employed | Medicare is primary | Enroll in Parts A and B at 65. Marketplace plan terminates. | 10% penalty per year of delay, permanent |
Important nuance: The 20-employee threshold counts all employees, full-time, part-time, and seasonal, across all locations. If you're unsure, ask your HR department for a written confirmation of employer size.
Should You Enroll in Part A if You're Still Working?
For most people, yes, Part A is premium-free if you or your spouse have 40+ quarters of Medicare-taxed employment. There's generally no reason to skip it.
The HSA exception: If you contribute to a Health Savings Account (HSA) through your employer, enrolling in any part of Medicare, including Part A, makes you ineligible to contribute to your HSA. Additionally, Part A enrollment is retroactive 6 months, which means if you've been contributing to your HSA during those 6 months, you may owe penalties.
According to IRS guidance, the recommended approach is:
- Stop HSA contributions at least 6 months before enrolling in Part A
- You can still use existing HSA funds, you just can't contribute new money
- HSA funds can be used to pay Medicare premiums (Part B, Part D, and Medicare Advantage, but not Medigap premiums)
What Happens When You Retire, How Does the Special Enrollment Period Work?
When you lose your employer coverage (by retiring, being laid off, or the coverage ending), you get a Special Enrollment Period (SEP):
- Part B SEP: 8 months from the date your employer coverage ends (not 8 months from your retirement date, these can differ)
- Part D SEP: 63 days from the date your creditable drug coverage ends
- Medigap OEP: If you're enrolling in Part B for the first time at age 65+, your 6-month Medigap guaranteed-issue window starts when Part B begins
Critical documents to collect from your employer:
- Letter confirming your coverage end date
- Certificate of Creditable Coverage (proves your employer plan was equivalent to Medicare)
- Employer size verification (confirms 20+ employees if applicable)
These documents are your protection against late-enrollment penalties. Keep them permanently.
Can You Have Medicare AND Employer Coverage at the Same Time?
Yes, this is called "coordination of benefits." Which plan pays first depends on employer size:
- Large employer (20+): Employer plan pays first (primary), Medicare pays second (secondary). Many people in this situation enroll in Part A only (free) and delay Part B.
- Small employer (under 20): Medicare pays first, employer plan pays second. You must have both Part A and Part B for proper coordination.
Having both can actually provide excellent coverage, the secondary plan picks up most of what the primary doesn't cover. However, be aware that if Medicare is primary and you don't have Part B, your employer plan may not cover the Part B portion of your bills.
What About COBRA, Does COBRA Count as Creditable Coverage?
No. This is one of the most dangerous misconceptions. COBRA is not considered creditable coverage for Medicare purposes. If you're 65+ and choose COBRA instead of enrolling in Medicare:
- You'll pay full COBRA premiums (often $600 to $2,000/month with no employer subsidy)
- COBRA does NOT protect you from Part B late-enrollment penalties
- You'll face penalties when COBRA ends and you finally enroll in Part B
According to CMS, COBRA continuation coverage does not count as "current employer coverage" for SEP purposes. Always enroll in Medicare before or instead of taking COBRA if you're 65+.
What If Your Spouse Works and You're on Their Employer Plan?
The same rules apply based on the spouse's employer size:
- Spouse's employer has 20+: You can delay Part B while covered under the spouse's plan without penalty
- Spouse's employer has under 20: Medicare is primary. You should enroll at 65.
When your spouse retires or you lose coverage, you get the same SEP, 8 months for Part B, 63 days for Part D.
Frequently Asked Questions About Working Past 65 with Medicare
What is the most common mistake people make when working past 65?
Working for a small employer (under 20 employees), not enrolling in Part B at 65, and then discovering the 10% penalty per year. This penalty is permanent and can add up to thousands over a lifetime. For example, delaying 3 years means a 30% surcharge on your Part B premium, an extra $60+/month, forever.
Can I delay Medicare if I'm self-employed?
No. Self-employed individuals don't have "employer coverage" in the Medicare sense. You should enroll in Parts A and B at 65. If you have a Marketplace plan, it will terminate when Medicare begins. If you have an HSA, stop contributions 6 months before enrolling.
My employer says I have to take Medicare at 65. Is that true?
Small employers (under 20) may require it because Medicare becomes your primary insurance. Large employers (20+) cannot force you to enroll in Medicare at 65, it's your choice. However, if you do enroll, the coordination rules apply.
Should I sign up for a Medicare Supplement while still working?
If you're delaying Part B, you can't enroll in a Supplement yet (Supplements require Part B). When you do enroll in Part B, whether at 65 or upon retirement, your Medigap Open Enrollment Period begins, giving you 6 months of guaranteed-issue rights. Don't miss this window. See our guide to popular Supplement plans.