Medicare Secondary Billing Without Guesswork: A Therapist's Guide to Getting Paid Correctly
You submitted the Medicare claim. Medicare paid its portion. Now there's still a balance sitting on the account… and you're wondering:
Do I bill Medicaid?
Do I bill the secondary insurance?
Will this cross over automatically?
Am I supposed to adjust this off?
If you've ever stared at a Medicare Explanation of Benefits (EOB) trying to figure out what happens next, this is one of the most common sticking points for therapists billing Medicare.
Medicare secondary billing isn't difficult because it's complicated. It's difficult because most therapists were never taught how the process actually works.
Understanding how the process works can reduce claim delays, minimize unnecessary patient balances, and help you collect reimbursement with confidence.
The money is already there. You just have to claim it.
This guide breaks down what's actually happening on your Medicare EOB and where practices typically lose money in the handoff to a secondary payer. Want the exact field-by-field workflow instead of piecing it together yourself? The Secondary Billing for Medicare Course walks through this process step by step, claim by claim.
Learn how Medicare secondary billing works, why so many therapists get stuck on it, and where practices lose revenue in the handoff between payers.
What Medicare Secondary Billing Actually Is
Medicare secondary billing is the practice of submitting a claim to a second payer after Medicare (the primary payer) has already processed and paid its portion.
It sounds simple in theory. In practice, it's one of the most under-taught parts of behavioral health billing and costs real practices real revenue every month.
That secondary plan might be an employer-sponsored plan, a spouse's private insurance, Medicaid, or another policy supporting Medicare. For the federal-level rules on payer responsibility, see the CMS overview of Medicare’s coordination of benefits.
It’s important to note that secondary insurance is not the same as a Medigap or supplemental policy - those typically cross over automatically, with the system forwarding the data for you.
(For a quick rundown of the difference between supplemental and secondary insurance, see Medicare Supplements vs. Secondary Insurance Explained.)
Secondary billing does not have that automatic handoff. You build and submit that second claim yourself.
Are you brand new to Medicare billing? Start here with Mastering Medicare Billing: A Guide for Beginners and Experts .
How Medicare and the Secondary Plan Split the Bill
Medicare doesn't pay your full charge. It pays based on the Medicare-allowed amount, the program's approved value for that service.
Whatever's left over - usually a deductible, coinsurance, or both - is what the secondary payer reviews next. If your patient has secondary insurance, that plan exists to pick up what Medicare left behind. You're entitled to bill for it.
That leftover amount isn't arbitrary, either! It comes directly from the numbers on the Medicare EOB.
If you skip the second step, that balance sits in your accounts receivable, even though another plan may still owe money on it.
Why This Trips Up Therapists and Small Practices
Most therapists never receive formal training on secondary claims.
Often, billing training stops at the primary claim, and secondary claims work a little differently, with rules most providers were never actually taught.
A practice can do practically everything right with Medicare billing and still leave money on the table, simply because a secondary claim was never filed or was filed incorrectly.
A secondary claim uses the same basic claim form as everything else you submit, but it requires additional information explaining what Medicare has already paid.
When these claims get rejected, it's rarely about the service you provided. Instead, it’s almost always that the numbers didn't add up correctly.
If you’ve ever heard "secondary insurance never pays correctly," it's usually an issue with how the claim was filled out, not a payer issue.
Fortunately, that's a solvable problem!
The Three Medicare EOB Numbers to Pull Before You File Anything
Before opening a secondary claim, pull these three numbers from the Medicare EOB.
Get one wrong, and the claim can be rejected outright, pay too short, or leave a balance that makes no sense.
| EOB Number | What It Tells You | Why It Matters |
|---|---|---|
| Allowed Amount | What Medicare says the service is worth | Sets the payment ceiling |
| Provider Check Amount | What Medicare actually paid you | Shows how much is already satisfied |
| Deductible and/or Coinsurance Amount | What remains after Medicare pays | Tells the secondary plan what's still open |
Allowed Amount, Provider Payment, and Patient Responsibility
Think of these three figures as one equation:
The allowed amount sets the total value Medicare recognizes.
The provider payment fills in part of that total.
Whatever's left (the patient's responsibility) passes to the secondary payer.
Even just a wrong number in the wrong field can cause the payer to read the claim differently than the EOB intended.
Deductible and Coinsurance Are Not the Same Thing
A deductible is the amount a client must pay before their plan kicks in.
Coinsurance is the share remaining after the deductible has been met. In real-world billing, you'll typically run into one of three situations:
The deductible isn't met yet
It's already met
The claim is a split - part deductible, part coinsurance
This distinction matters because the secondary payer may apply different rules to each figure.
When a secondary claim doesn't pay correctly, it's often because the deductible and coinsurance got blended together.
Where Secondary Claims Actually Go Wrong
This is where most practices get stuck.
The goal is simple: every dollar on the EOB needs to land somewhere on the secondary claim before you hit submit. Getting there is where it gets technical.
Start With the Finalized Primary Claim, Not a Blank Form
Don't build these claims from scratch unless you truly have to.
Start with the finalized primary insurance claim - it already has the client info, dates of service, billing codes, and diagnosis info that Medicare has already processed. This saves time, reduces typos, and works with any EHR, since the basic claim form stays the same even if the screens look different.
Prioritize the Coordination of Benefits Fields
This is the part of the form most therapists find genuinely confusing, and it's also where a single mistake is most likely to cause the whole claim to be rejected.
You're not just reporting what Medicare paid; you're telling the secondary payer how to interpret every remaining dollar, using a set of adjustment codes that serve as a built-in explanation attached to the claim.
If you pick the wrong code, or split a balance incorrectly between deductible and coinsurance, the claim can reject even when every dollar amount on it is technically correct.
Run the Balance Check Before You Submit
Before submitting anything, compare the claim to the EOB line by line (allowed amount, Medicare payment, deductible, coinsurance, and write-off). Then check what's left for the secondary insurer, including anything counting toward the patient's out-of-pocket maximum.
Patients pay monthly premiums expecting full coverage, so getting this right directly affects what they owe.
If a small balance remains after both payers process the claim, a health savings account can often cover it.
A balanced claim accounts for every dollar on the EOB before you hit submit.
If the numbers don't reconcile, don't send it and hope the payer sorts it out - fix the math first. This final review catches most avoidable rejections and turns secondary billing from a recurring headache into a routine part of your week.
The Most Common Medicare Secondary Billing Mistakes
Most rejections trace back to a short, predictable list of errors - either the EOB numbers were misread, or the wrong plan got billed first (this is common with active employment coverage or a special enrollment period).
1. Mixing up deductible and coinsurance. Post one as the other, or combine them into a single figure, and the secondary payer can't read the claim. This is especially costly on high-deductible health plans, where the math has to be exact.
2. Using the wrong code to explain the balance. These codes indicate to the payer why a charge remains outstanding. One wrong code can stall a claim even when every dollar amount is correct.
3. Assuming the secondary payer will catch the error. They only process what's sent, and won't fix a missing detail or a mismatched balance. The most expensive mistake is often no secondary claim at all, leaving a collectible balance unclaimed.
When to Get Help (And How to Learn This Faster)
If secondary billing is a “to-do” that’s left to be resolved, that's not a sign you're bad at billing.
It's likely a training gap, and once the logic clicks, the process gets much easier.
Secondary billing for Medicare is one piece of the larger picture. See How to Learn Medicare Billing as a Therapist for the full roadmap.
So far, I’ve explained what's happening on the EOB and why claims stall.
What it doesn't give you is the actual walkthrough: which field each number goes in, how to select the right adjustment code for your specific scenario, and how to catch a mismatch before you submit rather than after it's rejected.
That's the part that turns understanding into a paycheck.
That's exactly why fast-tracking your understanding matters more than muscling through it on your own. The Secondary Billing for Medicare Course was built exactly for this reason.
This mini-course was co-created with Rachel Regina, my co-admin in our Medicare Facebook community, and one of the sharpest people around when it comes to Medicare billing. It's self-paced, built around real Medicare EOBs and actual claim scenarios, and walks you through the exact fields, codes, and checks, not just the concepts behind them.
It shows the workflow inside SimplePractice, though it applies regardless of the EHR platform you use.
You don't need a billing background, and you don't need to have filed a secondary claim before. It starts at the beginning.
Even better? One recovered secondary balance can cover the cost of the course!
Final Thoughts
Medicare secondary billing no longer feels like a mystery once you stop guessing and start following a repeatable process.
Understanding what the EOB is telling you is the first step - knowing exactly where each number goes and how to verify the claim before you submit is what actually stops the rejections.
Properly coordinating benefits, starting with the primary claim, ensures that secondary claims cover the remaining copays and keep patient costs low.
Fewer rejections. Less guesswork. More revenue landing in your practice.
Secondary claims don't have to be confusing. Fast-track your Medicare secondary billing skills with the on-demand course and start collecting the reimbursement your practice has already earned.
Gabrielle Juliano-Villani, LCSW, helps healthcare organizations, online platforms, and mental health providers navigate Medicare & Medicaid with confidence. With over a decade of experience supporting mental health providers in navigating billing, compliance, and documentation, she now offers consulting and training to help others grow sustainable, compliant practices.