Medicare and Employer Coverage: What Happens When Your Parent Works Past 65

Your parent turned 65 last month but they're still working. They have health insurance through their employer. Do they need to sign up for Medicare? Do they keep their employer plan? Do they need both? What happens to their HSA?

These questions come up constantly, and the answers depend on details that most people don't think to ask about -- particularly the size of the employer. Getting this wrong can cost your parent thousands of dollars in lifetime penalties or leave them with surprise coverage gaps.

The 20-employee rule: the most important fact

The entire framework depends on one number: how many employees work for the company providing health coverage.

Employer with 20 or more employees

• Employer coverage is primary. The employer plan pays first for medical bills.
• Medicare is secondary. If your parent enrolls in Medicare, it picks up costs that the employer plan doesn't cover.
• Your parent can delay Part B without penalty. As long as they (or their spouse) have active employer group health coverage through a company with 20+ employees, the clock on Part B enrollment does not start. No penalty accumulates.
• Enroll in Part A. It's free and does not conflict with employer coverage. Part A will serve as secondary coverage for hospital stays.

The exception -- HSA accounts. If your parent has a Health Savings Account (HSA), enrolling in Part A creates a problem. Once enrolled in any part of Medicare, your parent can no longer contribute to an HSA. If they want to continue contributing to their HSA, they should delay both Part A and Part B.

Here's the complication: if your parent is receiving Social Security benefits, they are automatically enrolled in Part A. To keep HSA eligibility, they would need to delay Social Security benefits until they're ready for Medicare. If they're already receiving Social Security, they can stop Part A by withdrawing their Social Security application, but this requires repaying all benefits received. This is complex enough that it warrants a conversation with a financial advisor.

Employer with fewer than 20 employees

• Medicare is primary. Medicare pays first.
• Employer coverage is secondary. The employer plan fills in gaps after Medicare pays.
• Your parent should enroll in Part B at 65. Because Medicare is primary, delaying Part B means the employer plan may not cover the full cost of care. Some small-employer plans explicitly require Medicare enrollment at 65 and will reduce benefits if the employee does not comply.
• The penalty clock starts at 65. If your parent does not enroll in Part B and the employer has fewer than 20 employees, the late enrollment penalty begins accumulating immediately.

How to find out the employer size

Ask the employer's HR department or benefits administrator: "Is our group health plan subject to the Medicare Secondary Payer rules for employers with 20 or more employees?"

If the HR person is unsure, that's a red flag. Get it in writing. Some companies hover near the 20-employee threshold, and the count can include part-time and seasonal workers depending on specific rules. When in doubt, confirm with the plan administrator and keep documentation.

The coordination of benefits: who pays what

When your parent has both Medicare and employer coverage, the two plans coordinate benefits. One pays first (the "primary" payer), and the other pays second (the "secondary" payer). Understanding the order prevents surprise bills.

Large employer (20+): employer pays first

1. Your parent goes to the doctor
2. The employer plan processes the claim and pays its share
3. Any remaining balance goes to Medicare (if enrolled) as secondary
4. Your parent pays whatever's left

Small employer (under 20): Medicare pays first

1. Your parent goes to the doctor
2. Medicare processes the claim and pays its share
3. The remaining balance goes to the employer plan as secondary
4. Your parent pays whatever's left

Why this matters

If Medicare is supposed to be primary but your parent has not enrolled in Part B, there may be a gap where neither plan is covering the Part B portion of care. The employer plan expects Medicare to pay first and will only cover what's left. But Medicare isn't paying because your parent isn't enrolled. The result: your parent gets stuck with large bills that neither insurance covers.

This is most common with small employers where the parent didn't realize they needed to enroll in Part B at 65.

When your parent retires: the transition checklist

The day your parent stops working is when the rules change and the clock starts ticking. Here's the sequence:

Before the last day of work

• [ ] Get Form CMS-L564 from the employer's HR department. This form proves your parent had continuous employer coverage and is required to use the Special Enrollment Period for Part B without penalty
• [ ] Get the exact date employer coverage ends. It might be the last day of employment, the end of the month, or some other date depending on the employer's policy
• [ ] If your parent has an HSA, plan to stop contributions before Medicare enrollment begins

Within the first month after coverage ends

• [ ] Enroll in Part B using the 8-month Special Enrollment Period. Submit Form CMS-40B (Application for Enrollment in Medicare Part B) along with Form CMS-L564
• [ ] Choose supplemental coverage: Medigap or Medicare Advantage
• [ ] If choosing Medigap: Your parent enters their 6-month Medigap Open Enrollment Period when Part B starts. This is the guaranteed-issue window where no insurer can deny them or charge more due to health conditions. Do not miss this window
• [ ] Enroll in Part D (standalone drug plan) if going the Original Medicare + Medigap route. The Special Enrollment Period for Part D runs concurrently
• [ ] Decline COBRA for primary coverage (see below)

The COBRA decision

Your parent will likely be offered COBRA continuation coverage when employer coverage ends. Here is what you need to know:

COBRA does not count as employer group coverage for Medicare enrollment purposes. The 8-month Special Enrollment Period for Part B starts when employer coverage or employment ends -- not when COBRA ends. If your parent rides COBRA for 18 months thinking they can enroll in Part B afterward, the SEP will have expired. They'll face the General Enrollment Period (January-March), a coverage gap until July, and the permanent late enrollment penalty.

The safe approach: Enroll in Part B immediately when employer coverage ends. If there's a transition gap of a few weeks before Part B starts, COBRA can serve as bridge coverage. But Part B enrollment is the priority.

Can COBRA work alongside Medicare? Technically, yes. Your parent can have COBRA as secondary coverage while Medicare is primary. But COBRA premiums are expensive (100% of the plan cost plus a 2% administrative fee), so this rarely makes financial sense once Medicare and Medigap are in place.

Spouse coverage scenarios

The employer coverage rules apply whether the coverage is through your parent's own employment or through their spouse's employment. Some common scenarios:

Your parent is 65, retired, but covered under their younger spouse's employer plan (20+ employees): Your parent can delay Part B without penalty. The employer plan is primary. When the spouse retires or the coverage ends, the 8-month SEP applies.

Your parent is 65 and their spouse is also 65, both on the same employer plan: Both can delay Part B. When the employer coverage ends, both get their own 8-month SEPs.

Your parent is 65 and covered under a spouse's employer with fewer than 20 employees: Medicare should be primary. Your parent should enroll in Part B at 65.

The self-employment exception (there isn't one)

Self-employed individuals do not get the employer coverage delay benefit. If your parent is self-employed -- even if they have individual health insurance purchased through the marketplace or directly from an insurer -- that is not "employer group health coverage" for Medicare purposes.

Self-employed parents must enroll in Part B during their Initial Enrollment Period at 65, or face the penalty. Individual market plans, ACA marketplace plans, and short-term health insurance do not qualify for the SEP delay.

Questions families ask

"My parent's employer says they don't need Medicare because they have the company plan." The employer might be wrong, especially if they have fewer than 20 employees. Get clarification in writing. If the employer has fewer than 20 employees, your parent likely needs Part B at 65 regardless of the employer plan.

"Can my parent keep their employer plan AND have Medicare?" Yes. Having both is common. The question is which one is primary (pays first), which depends on employer size. There's no penalty for having both.

"My parent has retiree health benefits. Does that delay Part B?" No. Retiree health benefits are not the same as active employer group coverage. If your parent has retired and is receiving retiree health benefits, they should enroll in Part B. Retiree plans often require Medicare enrollment and may reduce or eliminate benefits if the retiree doesn't have Medicare.

"What if the employer changes from 20+ to under 20 employees?" The rules follow the current status. If the employer drops below 20 employees, Medicare becomes primary. Your parent should enroll in Part B to avoid a coverage gap. Monitor employer size if the company is near the threshold.

The intersection of Medicare and employer coverage is where most enrollment mistakes happen -- and where the financial consequences are steepest. If you want a structured guide that walks through every scenario, with a timeline tracker, documentation checklist, and the exact forms your parent needs, the Medicare Enrollment Guide covers it all for $14.