The Medicare Explanation of Benefits document — the EOB that Medicare sends after a service is used — is one of the most misunderstood documents in the American healthcare system. Most Medicare beneficiaries receive their EOB, look at the column of numbers, and file it without understanding what it is telling them. The ones who call their agent confused about it are giving you something valuable: an opportunity to demonstrate expertise, identify real coverage gaps, and have a substantive conversation about their plan's performance.
What the EOB Is (and What It Is Not)
An EOB is not a bill. It is a summary of what Medicare paid, what the provider accepted, and what — if anything — you owe. Confusing an EOB for a bill is so common that most EOBs now include "This is not a bill" in large print at the top.
The Five Columns to Understand
| EOB Column | What It Means |
|---|---|
| Billed amount | What the provider charged (often much higher than what was paid) |
| Medicare approved amount | What Medicare considers the legitimate cost for this service |
| Medicare paid | What Medicare Part A or B actually paid (usually 80% of approved) |
| You may be billed | What the provider can legally charge you after Medicare's payment |
| Deductible / Coinsurance | Amounts applied to your annual deductible or your 20% coinsurance share |
The Coverage Gap Signals in an EOB
A Large "You May Be Billed" Amount
If this column shows $500, $1,000, or more for a single service, this is the most direct demonstration of why Medigap coverage matters. "This column is the amount you are responsible for out of pocket. If you had a Plan G, this would be zero."
Services Showing "Not Covered"
Services marked as "not covered" reveal either: the service is genuinely excluded from Medicare (routine dental, vision, hearing aids), the claim was filed incorrectly, or prior authorization was not obtained. Walking a client through a "not covered" line item builds trust.
Repeated Small Coinsurance Charges
A pattern of recurring coinsurance charges is the economic case for Medigap in concrete numbers: "I can see you've had five visits this year with $35 to $50 in coinsurance each — that's $200 out of pocket so far. A Plan G would have covered all of that for about $X per month."
The EOB Review as an Annual Review Agenda Item
Adding "bring your last EOB" to the annual review invitation gives the conversation concrete structure. Instead of a generic "is your plan still working?" the annual review becomes a data-driven assessment of actual plan performance. This level of specificity separates genuine annual reviews from box-checking.
Frequently Asked Questions
References: CMS. (2024). Medicare Explanation of Benefits. How to read your Medicare Summary Notice. | CMS. (2023). Medicare.gov Authorized Representative Access.
