✔ Backed by: Centers for Medicare & Medicaid Services · Medicare.gov · HIV.gov (U.S. Department of Health and Human Services) · SHIP and SMP programs (supported by the Administration for Community Living). Each fact links to its source, and the full list is at the bottom of this post.
It shows up in the mail a few weeks after a doctor visit. It has rows of numbers, a few codes, and big letters across the top that say “THIS IS NOT A BILL.” Most likely, it’s an explanation of benefits. So what does that mean? And should you throw it away, file it, or call someone?
That paper is called an Explanation of Benefits, or EOB. If you have Original Medicare, you get a similar notice called a Medicare Summary Notice, or MSN. Learning to read one does not take long. And once you know how, it can help you catch billing mistakes, avoid paying more than you owe, and spot signs of fraud.
What an explanation of benefits is, and what it is not
An EOB is a statement from your health plan. It shows the total charges for a visit and how much the plan will cover. It is not a bill. It explains what you will likely owe when your provider sends the actual bill.[1]
Think of it like a receipt from your insurance company. It says, “Here is what the doctor asked for, here is what we agreed to pay, and here is the part that is left for you.”
Which one you get depends on your coverage. Original Medicare sends MSNs. Medicare Advantage and Part D drug plans send EOBs.[4] Other health insurance plans send EOBs, too.[1]
The key words, in plain language
The Centers for Medicare & Medicaid Services (CMS) breaks down the main parts of an EOB.[1] Here is what they mean:
- Claim number: The reference number for this claim. Have it ready when you call.
- Date of service and service description: When you got care and what it was, like an office visit or lab test.
- Provider charges: What the provider billed.
- Allowed charges: The amount the provider will actually be paid. It may be lower than what they billed.
- Paid by insurer: What your plan paid.
- What you owe (patient balance): What is left for you after the plan pays its share.
- Remark codes: Short codes with notes about the costs or payments. Look for their meanings at the bottom of the EOB.
Why is the “provider charges” number often so much bigger than the “allowed” number? HIV.gov explains that insurers often negotiate lower contracted rates with providers.[2] So a big first number does not always mean a big bill for you. The part you owe can include your deductible, copay, or coinsurance.[2]
A simple four-point check for your explanation of benefits
When an EOB or MSN arrives, sit down with your calendar or appointment notes and check these four things.
1. Did you actually get this care? Make sure the dates, provider name, and services match what really happened.[2] Medicare.gov suggests comparing your records to your MSN to be sure you got every service, supply, or piece of equipment listed.[3]
2. Is your information right? Check that your name and plan information are correct.[1]
3. Does the bill match? When the provider’s bill comes, compare it to the patient balance on your EOB. CMS says the bill should not be higher than the patient balance. If it is, contact your provider.[1] Keep in mind that the EOB does not show payments you already made, like a copay at the front desk.[1]
4. Anything strange? HIV.gov lists red flags to watch for: services you did not receive, duplicate charges, wrong medicine charges, charges for care you canceled, and costs that are much higher than expected.[2]
For example, picture Denise. She opens an EOB and sees a charge for a physical therapy visit on a day she was out of town. She circles it, calls the number on the EOB, and learns it was billed under the wrong date. One phone call gets it fixed.
If something looks wrong
Start with a phone call. If a bill looks wrong, contact the provider’s billing office or your health plan. Keep notes on each call, including the date and the name of the person you spoke with.[2]
You can say: “Hi, I’m calling about claim number [read the number]. My Explanation of Benefits shows a service on [date] that I don’t recognize. Can you help me understand what this is?”
If a claim was denied, the EOB should tell you the reason. It may also explain how to appeal or ask for another review.[2] With Original Medicare, a denial is sometimes just a paperwork mix-up. Medicare.gov suggests contacting the provider’s office to make sure they sent the right information, since they may be able to resubmit. If you disagree with a decision, the last page of your MSN gives step-by-step directions on when and how to file an appeal.[3]
For questions about surprise billing protections, you can call the No Surprises Help Desk at 1-800-985-3059. Help is offered in English, Spanish, and more than 350 other languages.[1] And if you cannot afford a bill that is correct, ask your provider about payment plans or financial assistance.[2]
Spotting possible Medicare fraud
Your MSN or EOB is one of the best tools you have to catch Medicare fraud early. Ask your provider or plan about questions or errors first. If a provider will not fix a mistake, or a charge looks suspicious, contact your local SMP (Senior Medicare Patrol) at 877-808-2468 or smpresource.org. For help understanding Medicare notices, your State Health Insurance Assistance Program (SHIP) can help at 877-839-2675 or shiphelp.org.[4]
The SMP program also offers a “My Health Care Tracker” to log your appointments so checking statements is easier.[4]
Paper, online, and privacy
If you have Original Medicare, you can choose electronic MSNs. You get an email with a link for any month with a processed claim. Large print and Braille versions are also available.[3]
Privacy is worth a thought, too. EOBs may go to the main policyholder by mail or show up in an online insurance account, so someone else on your plan might see them. If that worries you, ask your plan about confidential communications, a different mailing address, or electronic delivery. Store your EOBs and bills somewhere safe.[2]
Tru-Tips: Keep a simple folder labeled “EOBs and Bills.” When a provider bill arrives, staple it to the matching EOB. Wait to pay until you have both, because the EOB may not show the final amount until the bill arrives.[2]
One Tru Step: Find your most recent EOB or MSN this week. Pick one line and check it against your calendar. Did you get that care on that date? That one check is the habit that catches mistakes.
Let’s talk
Have you ever caught a mistake on an EOB or Medicare Summary Notice? What tipped you off? Share your story or your best tip for staying organized with health paperwork.
Sources and further reading
- Centers for Medicare & Medicaid Services: How to read an explanation of benefits (EOB)
- HIV.gov: Understanding Your Explanation of Benefits (EOB)
- Medicare.gov: Medicare Summary Notice (MSN)
- SHIP and SMP: MSNs and EOBs
Sources checked October 21, 2026. General education; individual care and coverage questions require an appropriate professional.
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