Employer Size Misclassification: How a Headcount Error Creates Medicare MSP Liability Here's the situation. You've got 18 full-time employees. You're confident your employer group health plan is secondary for Medicare-eligible employees —because with fewer than 20 employees, Medicare is primary under the Medicare Secondary Payer rules. So you've structured your claims processing accordingly.
But six months ago, you hired four new people. You didn't update your MSP classification. And now a claim comes through from a Medicare-eligible employee, and your plan pays as secondary when it should have paid as primary.
You've just created a coordination error that could expose your plan to liability and cost recovery demands from CMS.
Employer size misclassification is one of the most overlooked Medicare compliance failures—and one of the most expensive when it goes uncaught. Because the MSP rules hinge on headcount, and headcount changes constantly. Here's what every employer needs to understand about why size matters, how to verify your classification, and what happens when you get it wrong.
Why the 20-Employee Threshold Changes Everything The Medicare Secondary Payer statute draws a hard line at 20 employees. If your organization employs 20 or more workers, your employer group health plan is primary for active employees aged 65 and older . Medicare is secondary—it pays after your plan does. Drop below that number, and the order reverses: Medicare pays first, and your plan picks up whatever remains.
This isn't a soft guideline. It's a hard break that determines which payer bears the cost of claims, how your plan's claims system must be configured, and how your employees should be counseled about their coverage options .
Nineteen employees: Medicare is primary . Twenty employees: your plan is primary. The difference isn't small.
There's also a second threshold worth knowing. For disabled employees under 65, the relevant number is 100 employees . If you employ 100 or more workers and have a disabled employee on Medicare who is still actively employed, your group plan is primary. Below 100, Medicare leads. Again, the threshold creates a firm break in the coordination order.
The point: your headcount isn't just a demographic—it's a compliance trigger. If you don't know your exact size, you don't know your coordination rules.
How Employers Miscount (and Stay Miscounted) The counting rule sounds deceptively simple: count all employees on the payroll. But small employers—especially those hovering near the 20-employee line —often get this wrong in ways that persist for years.
Common miscounting mistakes include:
Counting only full-time employees. Part-time workers on payroll count for MSP purposes, even if they're not benefits-eligible.Excluding seasonal workers. If they're on the payroll, they count.Operating from a general impression. "We're around 18 people" is not a compliance position.Measuring at a single point in time. The IRS has specific rules for how to count across the year—and a one-time snapshot doesn't satisfy them.Most employers who misclassify didn't do it intentionally. They hired someone new, or brought on a contractor who transitioned to W-2, and simply never revisited their MSP classification. Time passes. Claims keep processing under the old rules. And eventually—either through a CMS audit or an unexplained claims discrepancy—the gap surfaces.
By that point, the question isn't just how to fix it. It's how far back the error goes.
What Happens When Your Classification Is Wrong When CMS determines that an employer has been incorrectly classified, the financial liability falls on the plan. The scope of that liability depends on how long the error persisted and how many Medicare-eligible employees were affected.
In practical terms:
If your plan paid as secondary when it should have been primary , CMS may demand recovery for the difference between what Medicare paid (as the "wrong" primary) and what it should have paid as the secondary payer.If your plan paid as primary when Medicare should have led , you may owe recovery for claims your plan processed that Medicare should have handled .If the error is caught within a year or two, recovery is usually limited to that window. If it's been ongoing for five or more years, the exposure can be substantial. CMS will review claims for all Medicare-eligible employees during the period of misclassification and calculate the gap between what was actually paid and what should have been.
There's also a compliance dimension beyond the dollar amount. If CMS determines the employer was negligently misclassified over an extended period, it can impose additional penalties or audit other aspects of your claims-processing procedures. Recovering overpayments from employees or providers adds another layer of administrative cost and complexity.
Employer size misclassification is correctable—but it's far less painful to correct it yourself than to have CMS discover it first.
How to Verify and Document Your Classification The safest approach is to count your employees formally, at least once a year, and document the count. Here's how to do it right:
Run a complete payroll list. Include full-time, part-time, and seasonal employees. Don't rely on HR headcount estimates or benefits-enrollment numbers—those reflect a subset of your actual workforce. Apply the correct counting method. Consult IRS guidance on what constitutes employment for MSP purposes. The standard is more inclusive than many employers assume. Determine your MSP classification. Based on your count: Are you a small employer (fewer than 20)? A large employer (20 or more)? Does the 100-employee disabled-worker threshold apply to your situation? Document everything. Write down the count, the date, and the resulting classification. Save it. This documentation is your evidence if CMS ever questions how you've been processing claims. Communicate the classification to your TPA or plan administrator. They need to know your size to configure claims processing correctly. If you've crossed a threshold since your last update, the transition may require changes to your claims system—plan ahead. Revisit when headcount changes materially. You don't need to recount after every hire or termination, but if you're near a threshold—say, 18 or 22 employees—each staffing change carries compliance weight. Stay close to the number.Employers who can demonstrate a documented, consistent approach to MSP classification are far better positioned if CMS ever comes asking. You're not claiming perfection—you're demonstrating diligence.
The Bottom Line for Ohio Employers Medicare Secondary Payer rules don't come with a grace period for misclassification. If your headcount has changed, your compliance status may have changed too—whether you know it or not.
The fix isn't complicated. Count your employees. Document the count. Update your plan administrator. Repeat annually, or whenever headcount shifts significantly. If you're unsure whether your current classification is correct, or if you've recently hired across a threshold, that's exactly the kind of question a Medicare compliance review can answer before it becomes a recovery demand.
At Exact Benefits , we help Ohio employers stay on the right side of MSP rules—so a headcount change doesn't become a liability.
Next in the Exact Benefits newsletter: COBRA vs. Medicare: Which Pays First? — one of the most misunderstood coordination questions in employer benefits.
Frequently Asked Questions How do I know if my company is considered a small or large employer under Medicare Secondary Payer (MSP) rules? The Medicare Secondary Payer rules generally use the number of employees to determine whether your employer-sponsored health plan or Medicare pays first. If you're unsure how your workforce should be counted or whether you've crossed an important threshold, Exact Benefits can help you review your employee count and determine the correct MSP classification based on current Medicare guidelines .
What happens if my business has been using the wrong MSP classification? Using the wrong MSP classification can lead to claims being paid incorrectly, which may result in recovery requests from the Centers for Medicare & Medicaid Services (CMS), administrative challenges, and potential compliance issues. Exact Benefits works with employers to identify possible classification errors, review their Medicare coordination process, and help reduce the risk of future liabilities.
Should I update my Medicare coordination rules every time my employee count changes? You don't necessarily need to update your classification after every hire or termination, but you should regularly monitor your workforce, especially if your business is close to the 20-employee or 100-employee thresholds. Exact Benefits can help you determine when a staffing change may affect your Medicare Secondary Payer responsibilities and whether updates are needed.
Can Exact Benefits help our HR team understand Medicare Secondary Payer compliance? Yes. Exact Benefits partners with HR teams, benefits administrators, and employers to simplify Medicare compliance. We provide guidance on Medicare Secondary Payer rules, employee eligibility , employer size classifications, and coordination of benefits so your organization can make informed decisions and reduce compliance risks.
How can Exact Benefits help prevent Medicare MSP compliance mistakes? Exact Benefits provides personalized Medicare consulting , employer education, and ongoing support to help organizations stay compliant with Medicare rules . Our team can review your Medicare processes, assist with employee education, and help ensure your health plan coordination aligns with current Medicare Secondary Payer requirements, giving both employers and employees greater confidence in their coverage decisions.
