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April 14, 2026

Medicare Explanation of Benefits: Why You Got That Letter and What to Do With It

Why an EOB isn’t a bill, how to read a Medicare Summary Notice, deductibles, coinsurance, and how to spot billing errors.

If you're on Medicare, you periodically receive a document called an Explanation of Benefits, or EOB. Many Medicare recipients find these letters confusing — and some mistake them for a bill, which they are not. This guide explains what an EOB actually is, how to read it, and when to take action.

An EOB is not a bill

This is the single most important thing to understand. The Explanation of Benefits is a summary of medical claims that were submitted to Medicare on your behalf. It shows what was billed, what Medicare approved, what Medicare paid, and what — if anything — you may owe. But the EOB itself is not a request for payment. If you owe anything, a separate bill will come from your doctor or provider.

Original Medicare sends a Medicare Summary Notice

If you have Original Medicare (Part A and Part B), your EOB is called a Medicare Summary Notice, or MSN. It arrives quarterly and covers all the claims submitted during that period. If you have Medicare Advantage (Part C) through a private insurance company, your EOB comes from that insurance company and may look different, but contains the same basic information.

How to read the Medicare Summary Notice

The MSN lists each claim by date of service and provider. For each claim it shows the amount billed by the provider, the Medicare-approved amount (which is almost always lower — Medicare negotiates rates with providers), the amount Medicare paid, and the amount you may be responsible for. The "you may be responsible for" column is the important one if you're trying to understand whether a bill you received is legitimate.

Your deductible and coinsurance

Medicare Part B has an annual deductible — once you've met it for the year, Medicare starts covering its 80% share of approved costs. Your 20% share is called coinsurance. This is why you receive bills from doctors even when Medicare is active — they're billing you for your 20%. If you have a Medigap supplement policy, it may cover some or all of that 20%.

How to spot errors on your EOB

Medical billing errors are surprisingly common. When you receive an MSN or EOB, compare the dates and services listed against your own records. Did you actually see that provider on that date? Does the service listed match what was done? If something appears that you don't recognize — a service you didn't receive, a provider you never saw — it could be a billing error or, in rare cases, fraud. You can report discrepancies to Medicare at 1-800-MEDICARE.

The "appeals" section

Every EOB includes information about your right to appeal if Medicare denied a claim or paid less than you believe it should. Appeals have deadlines, so don't set the document aside if you believe a claim was incorrectly handled.

If you receive a Medicare document that you can't fully understand, you can upload it to ReadMyPay.com and get a plain English explanation of what it's saying and what, if anything, you need to do. Nothing is stored or saved.

Frequently asked questions

Is a Medicare Explanation of Benefits a bill I need to pay?
No. A Medicare Explanation of Benefits, also called an EOB or Medicare Summary Notice, is not a bill. It is a summary of medical claims submitted to Medicare on your behalf. It shows what was billed, what Medicare approved, what Medicare paid, and what you may be responsible for. If you owe any amount, a separate bill will come directly from your doctor or healthcare provider. Never send payment in response to receiving an EOB alone.
How do I read a Medicare Summary Notice?
A Medicare Summary Notice lists each medical claim by date of service and provider. For each claim it shows four key amounts: the amount your provider billed, the Medicare-approved amount (which is usually lower because Medicare negotiates rates), the amount Medicare paid, and the amount you may owe. Focus on the last column — your potential responsibility. Compare it against any bills you have received from providers to verify the amounts match. If a provider bills you for more than your Medicare Summary Notice says you owe, contact Medicare.
What is the difference between Original Medicare and Medicare Advantage for EOBs?
If you have Original Medicare (Part A and Part B), your EOB is called a Medicare Summary Notice and is sent by the federal government quarterly. If you have Medicare Advantage, also called Part C, your EOB comes from the private insurance company managing your plan and may look different in format. Both documents serve the same purpose — summarizing what was billed, what was paid, and what you may owe — but the branding, layout, and frequency of mailing can vary between Medicare Advantage plans.
How do I spot a billing error or possible fraud on my Medicare statement?
When your Medicare Summary Notice or EOB arrives, compare every listed service against your own records. Ask yourself: did I actually see this provider on this date? Was this service performed? Does the description match what happened at my appointment? If you see a service you did not receive, a provider you never visited, or a date when you were not at a medical facility, report it to Medicare at 1-800-MEDICARE. Medicare fraud is unfortunately common and costs the healthcare system billions annually. Your report can make a difference.
What is my right to appeal if Medicare denied a claim?
You have the right to appeal any Medicare decision to deny, reduce, or end coverage for a service you believe should be covered. Every EOB and Medicare Summary Notice includes information about your appeal rights and the deadline to file. These deadlines are important — missing them can forfeit your right to appeal. If you believe a claim was incorrectly denied or paid at the wrong amount, you can request a redetermination by contacting Medicare or your Medicare Advantage plan directly. AARP and local State Health Insurance Assistance Programs offer free help with Medicare appeals.

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