Medicare Conversion: How to Switch Your Parent from Employer Coverage to Medicare

Your parent has been on employer health insurance for decades. Now they're approaching 65, or retiring, or their company is downsizing — and suddenly you're both staring at a deadline to "convert" to Medicare. Getting this transition wrong can mean permanent lifetime penalties, unexpected coverage gaps, or losing access to the Medigap plan that would protect them best. Getting it right requires understanding exactly when Medicare kicks in, when it's safe to delay, and how to sequence the enrollment steps.

This guide walks through the complete employer-to-Medicare conversion process for adult children navigating it on a parent's behalf.

What "Medicare Conversion" Actually Means

"Medicare conversion" is an informal term for the process of transitioning a parent off employer-sponsored or retiree group health insurance and onto Medicare as their primary coverage. This isn't a single form — it's a coordinated sequence of decisions involving:

• When to enroll in Medicare Part A and Part B
• Whether existing employer coverage qualifies as "creditable" (which determines whether penalties apply)
• How to fill the gap that Original Medicare leaves (Medigap or Medicare Advantage)
• How to coordinate benefit-period timing so there's no coverage lapse

The stakes are high because some of these decisions are effectively permanent. A late Part B enrollment means a lifetime penalty added to premiums. Delaying Medigap enrollment past the guaranteed-issue window means medical underwriting — and potentially being denied coverage based on pre-existing conditions.

The Rule That Determines Everything: Employer Size

The single most important factor in any Medicare conversion is the size of your parent's employer. Federal law (the Medicare Secondary Payer rules) divides this cleanly:

Employer with 20 or more employees: The group health plan is the primary payer. Medicare is secondary. Your parent can delay Medicare Part B enrollment without penalty for as long as they remain actively employed and covered by the employer plan.

Employer with fewer than 20 employees: Medicare becomes the primary payer at age 65, even if your parent is still working and has employer coverage. The small-group plan becomes secondary — and may pay little or nothing unless Medicare pays first. If your parent hasn't enrolled in Medicare Part B, the insurer can legally deny claims that Medicare "would have" covered, leaving your parent personally responsible for those costs.

This is one of the most dangerous traps in all of Medicare. A parent working at a small business who skips Part B at 65 can end up with catastrophic unpaid medical bills — not because they lacked insurance, but because they had the wrong type at the wrong time.

Action step: Before your parent turns 65, call their HR department and ask directly: "Does our group health plan remain primary payer over Medicare for employees at age 65?" Document the answer. If they're at a small employer, Medicare Part B enrollment at 65 is not optional.

When It's Safe to Delay Medicare Part B

If your parent works for a large employer (20+ employees) and has active employee coverage — not COBRA, not retiree coverage — they can legally delay Part B enrollment using what's called the Special Enrollment Period (SEP) for employer coverage.

Here's how the SEP works:

• Your parent can enroll in Part B at any time while still employed and covered under active employer insurance
• After employment ends or coverage terminates (whichever comes first), they have an 8-month window to enroll in Part B without penalty
• The 8-month clock starts the day after the employer coverage or employment ends — not the date the insurer sends a termination notice

Critical distinction: COBRA and retiree health coverage do not count as "active employer coverage" for SEP purposes. If your parent retires and switches to COBRA or a retiree health plan, the 8-month SEP clock starts immediately — even if they're still on those plans. Many families miss this and assume they have more time than they do.

What About Retiree Health Coverage?

Many parents retire from government jobs, unions, or large corporations with retiree health benefits. These plans are common among teachers, firefighters, and long-tenure corporate employees.

Retiree coverage does not allow you to delay Medicare Part B. Once your parent retires, their SEP window opens. They need to enroll in Part B within 8 months of retirement, or they face the late enrollment penalty.

However, retiree health plans often work well alongside Medicare. Many are designed to "wrap around" Medicare — Medicare pays first, the retiree plan pays the remainder. In these arrangements, the retiree plan often becomes the equivalent of a Medigap supplement. Before assuming your parent needs to buy a separate Medigap policy, check what their retiree plan actually covers when Medicare is primary.

Questions to ask the retiree plan administrator:

• Does the plan become secondary to Medicare automatically when my parent enrolls in Part B?
• What does it cover after Medicare pays (deductibles, coinsurance, excess charges)?
• Does the plan have an annual premium once it's secondary to Medicare?
• Are there any benefits (dental, vision, prescription drugs) the plan continues to cover that Medicare doesn't?

The Part B Late Enrollment Penalty — and Why It's Permanent

If your parent misses their enrollment window — whether the Initial Enrollment Period (IEP) or the 8-month SEP after coverage ends — and goes without Part B for any period without a qualifying exception, they face a permanent penalty.

The penalty is 10% of the standard Part B premium for every 12-month period they went without creditable coverage. In 2026, the standard Part B premium is approximately $202.90 per month.

Example: Your parent retired at 65, switched to COBRA for 18 months thinking they were still covered, and enrolled in Part B at age 67. The 18 months on COBRA don't count as employer coverage for SEP purposes, so they have a 12-month late-enrollment period.

Penalty: 10% of $202.90 = $20.29 added to their monthly premium — forever. Over 20 years, that's nearly $4,900 in unnecessary extra costs.

The math gets much worse with longer delays. A parent who delays 3 years faces a 30% permanent surcharge.

The Medigap Window: The Most Time-Sensitive Decision in the Conversion

When your parent enrolls in Medicare Part B — whether at 65 during their IEP or later via the SEP — a critical 6-month clock starts. This is the Medigap Open Enrollment Period, and it is the most financially consequential window in the entire Medicare conversion process.

During these 6 months, your parent has guaranteed-issue rights to any Medigap policy available in their state. Insurers cannot:

• Ask about pre-existing conditions
• Charge higher premiums based on health status
• Deny coverage for any reason

Once those 6 months pass, guaranteed issue ends in most states. If your parent wants to add a Medigap policy later — say, at age 72 when a health problem emerges — insurers can deny them coverage or charge prohibitively high premiums based on medical underwriting.

This window does not reset every year. It is a one-time opportunity tied to the initial Part B enrollment date.

Practical consequence: If your parent is converting from employer coverage to Medicare, their Medigap enrollment window opens the day their Part B becomes effective. The conversion plan must include a Medigap policy decision made before or immediately upon Part B taking effect — not months later after they've "settled in."

Step-by-Step: The Medicare Conversion Sequence

Step 1: Determine employer size and confirm primary payer status (3-6 months before transition)

Call HR. Get written confirmation of whether the employer plan remains primary after age 65. If the employer is small (under 20 employees), your parent needs Part B immediately at 65 regardless of employment status.

Step 2: Establish Part A enrollment (typically at or near 65)

Most people are auto-enrolled in Part A when they start receiving Social Security. If your parent isn't receiving Social Security, they need to apply for Part A at SSA.gov. Part A has no monthly premium for those with 40+ work quarters and carries minimal risk — enroll in Part A without delay even if delaying Part B.

Step 3: Time the Part B enrollment precisely

For large-employer situations: enroll in Part B during the 8-month SEP window after employer coverage or employment ends, whichever comes first. Don't wait until month 7 or 8. Aim for month 1-2 to give yourself time to also select Medigap or Medicare Advantage.

For small-employer or retirement situations: enroll during the IEP (the 7-month window surrounding the 65th birthday, starting 3 months before).

Step 4: Select Medigap or Medicare Advantage during the guaranteed-issue window

This is the fork in the road for the rest of your parent's healthcare life. The research shows that Original Medicare plus a Medigap Plan G provides the most comprehensive, predictable coverage — especially for parents with existing or developing health conditions. Medicare Advantage often appears cheaper upfront but can cost far more in a serious illness year and may restrict access to specialists.

For most adult children navigating a parent's conversion, Plan G is the safest default unless:

• Their retiree plan already provides equivalent Medigap-level supplemental coverage
• The parent is in excellent health, has very low utilization, and fully understands the locked-in nature of the MA-to-Medigap switch

Step 5: Select a Part D drug plan (or confirm the retiree plan covers drugs)

If your parent's retiree plan includes prescription drug coverage, check whether it qualifies as "creditable coverage" — meaning it's at least as good as standard Part D coverage. If it is, they can delay enrolling in a stand-alone Part D plan without penalty. If it's not creditable, they need to enroll in Part D during their IEP or within 63 days of losing that coverage.

Step 6: File CMS-1696 if you're managing this on their behalf

To legally speak to Medicare representatives, view claims, or manage appeals on a parent's behalf, you need Form CMS-1696 (Appointment of Representative) on file with CMS. A general Power of Attorney does not grant this authority — Medicare requires its own authorization form.

Common Mistakes in the Medicare Conversion

Assuming COBRA extends the SEP clock. It doesn't. COBRA is not employer-sponsored active coverage. The 8-month Part B window starts the moment the active employer coverage ends, even if COBRA continues.

Waiting to compare Medigap plans. Every day you delay after Part B becomes effective is a day spent inside the guaranteed-issue window. Use those 6 months — don't assume you can shop for Medigap later.

Choosing Medicare Advantage during the conversion because it's free. The $0 premium is real. The locked-in nature of the conversion is also real. Once your parent develops health conditions and wants to switch back to Original Medicare plus Medigap, they may be medically denied. The conversion decision is not easily reversible.

Forgetting IRMAA. If your parent's income was high in the 2 years before Medicare enrollment — the year used to calculate IRMAA surcharges — they will pay above the standard Part B and Part D premiums. File Form SSA-44 with the Social Security Administration if income has recently dropped (due to retirement) to request a reassessment based on current income.

Making the Conversion Without Stress

The Medicare conversion from employer coverage is one of the most logistically complex things adult children help their parents navigate. The research, timing, and coordination required is exactly what the Medicare Enrollment Guide covers in full detail — including enrollment period charts, Medigap plan comparisons, a Part D selection walkthrough, and conversation scripts for discussing these decisions with a parent who may be resistant or confused.

A well-managed conversion protects your parent from lifetime penalties and guarantees them access to the broadest possible network of doctors and specialists, just when their health needs are likely to increase.