Medicare and Employer Health Plans: The 20-Employee Rule in Ohio (2026)

The 20-employee rule

The Medicare Secondary Payer rules — codified in federal law and CMS regulation — set up a binary based on employer size:

• 20 or more employees at the employer: the employer's group health plan (GHP) is primary. Medicare is secondary. The GHP must offer you the same coverage as younger employees and cannot push you off the plan because of Medicare eligibility.
• Fewer than 20 employees: Medicare is primary. The employer's plan is secondary (or may not cover you at all once you're Medicare-eligible).

The 20-employee count is calculated under specific federal rules — generally, employees on each working day in each of 20 or more calendar weeks in the current or preceding year. Sole proprietorships, partnerships, and certain other small employers may not meet the 20-employee threshold even if they have multiple workers. If you're unsure, ask your HR department or benefits administrator for the formal Medicare Secondary Payer determination.

Primary vs. secondary payer

Primary means: when you have a medical bill, this is the insurance that pays first. The primary payer reduces the bill to its allowed amount, applies its deductible and cost-sharing, and pays its share.

Secondary means: this insurance pays second. After the primary has paid, the secondary may pay some or all of the remaining amount, depending on its rules and what's already been paid.

The practical implications for working Ohioans past 65:

• If you work for a 20+ employer and have GHP coverage, you can delay Part B without enrollment penalties. The GHP pays first; you're protected from Medicare's late-enrollment penalty for as long as you have active employer coverage.
• If you work for a small employer (fewer than 20), Medicare is primary even though you have employer coverage. Skipping Part B means the bulk of your medical bills go unpaid until you enroll in Medicare. Many small-employer plans also have provisions that require you to enroll in Medicare at 65 — read the plan document carefully.

Why COBRA is not creditable for Part B

This is the single most expensive misconception in Medicare. COBRA continuation coverage does NOT count as creditable coverage for delaying Medicare Part B enrollment without penalty.

Here's what people commonly get wrong: COBRA gives you the legal right to continue your former employer's health insurance for up to 18 months (sometimes 36 months in specific situations) after you stop working. Many retiring Ohioans assume "I have insurance through COBRA, so I'm fine delaying Medicare." That's wrong.

The federal rule is: your Medicare Part B Special Enrollment Period starts the day your active employer coverage ends, not when COBRA ends. You have 8 months from that date to enroll in Part B without a late-enrollment penalty. If you spend 18 months on COBRA and then enroll in Part B, you've missed your SEP by 10 months — and the late-enrollment penalty applies for life.

The Medicare Secondary Payer notice

If your employer has 20+ employees and you're enrolled in their plan past 65, the employer is required to send you a Medicare Secondary Payer notice each year confirming that the employer plan is primary. Save these notices — they're proof of creditable coverage if you ever need to demonstrate to Medicare that you delayed Part B legitimately and shouldn't face a late-enrollment penalty.

If your employer hasn't sent you an MSP notice, ask. Without documentation, proving creditable employer coverage to Medicare can require additional paperwork through your former employer's HR or benefits administrator using Form CMS-L564 (Request for Employment Information).

Small-business employees: enroll at 65

If you work for an Ohio small business — fewer than 20 employees — the rules essentially require you to enroll in Medicare at 65, both Part A and Part B. Common Ohio scenarios:

• Family-owned restaurants, retail shops, and service businesses.
• Independent professional practices (law, accounting, healthcare provided in a small clinic).
• Small contractors and trades.
• Some farm operations and agricultural employers.

If you're in this situation:

1. Enroll in Medicare Part A and Part B during your 7-month Initial Enrollment Period around your 65th birthday.
2. Check your employer plan document for Medicare coordination — many small-employer plans become secondary or have reduced benefits once Medicare is primary.
3. Consider whether your employer plan is even worth keeping. Many Ohio retirees in small-employer plans find that Medicare + Medigap or Medicare Advantage costs less than the employer plan share for an active employee over 65.

Large-employer Ohioans: you can delay

If you work for an Ohio employer with 20+ employees and you have GHP coverage, you can safely delay Medicare Part B (and often Part A, though Part A is generally worth taking because it's free). Common Ohio examples:

• Cleveland Clinic, OSU Wexner Medical Center, University Hospitals, Mercy Health, TriHealth, Premier Health — the major hospital systems are all large employers.
• Procter & Gamble, Kroger, JPMorgan Chase, Nationwide, AEP, FirstEnergy, Marathon Petroleum, Sherwin-Williams — Ohio's large private employers.
• Federal civilian employees at Wright-Patterson AFB, NASA Glenn, DSCC, and other federal installations — FEHB is treated similarly to large-employer GHPs.
• State of Ohio employees — through OPERS-covered positions, with state employee health plans.
• Major Ohio universities — Ohio State, Case Western Reserve, University of Cincinnati, Bowling Green, Ohio University, Kent State.

For these Ohioans, the typical pattern is to delay Part B until retirement, then enroll during the 8-month SEP that begins when active employer coverage ends. The HSA conflict (see HSAs and Medicare) is a separate consideration if your employer plan is an HDHP.

Ohio employer landscape

Ohio's employer landscape is unusual in that it has both an exceptionally strong large-employer base (hospitals, manufacturing, financial services) and a large number of small businesses, family farms, and rural employers. The 20-employee rule can produce strikingly different Medicare outcomes for neighbors:

• A 67-year-old nurse at Cleveland Clinic (over 70,000 employees) is on the hospital's GHP, delaying Part B, with no penalty risk.
• A 67-year-old hairstylist at a 4-chair salon is on a small-group plan or individual market plan — Medicare is primary, and not enrolling in Part B at 65 created an enrollment problem.

If you're uncertain about your employer's Medicare classification, ask HR for the formal Medicare Secondary Payer determination in writing.