Frequently Asked Questions
What is a Medicare Explanation of Benefits?
An Explanation of Benefits (EOB) is a document from Medicare or your Medicare Advantage plan that explains how a claim was processed. For Original Medicare, this document is called the Medicare Summary Notice (MSN) and arrives quarterly by mail (or is available online at MyMedicare.gov). For Medicare Advantage, it's typically called an EOB and arrives after each claim is processed. The EOB is not a bill — it shows what was billed, what Medicare paid, and what you may owe.
How often does Medicare send an Explanation of Benefits?
Original Medicare sends Medicare Summary Notices (MSNs) quarterly — covering all claims from that 3-month period. Medicare Advantage plans typically send EOBs after each claim or monthly. You can view your claim information anytime at MyMedicare.gov without waiting for the mailed document. Signing up for the online account also provides faster access and the ability to flag suspicious claims.
What are common Medicare billing errors?
Common Medicare billing errors include: duplicate billing (the same service billed twice), upcoding (billing for a more expensive service than was actually provided), unbundling (billing separately for services that should be billed together), billing for services not rendered, incorrect diagnosis codes that affect coverage determination, and billing for non-covered services without an Advance Beneficiary Notice. Studies estimate 3–10% of Medicare claims contain errors.
How do I dispute a Medicare billing error?
For Original Medicare: request a redetermination (appeal) within 120 days of receiving the Medicare Summary Notice. For Medicare Advantage: file a grievance with your plan within 60 days. For suspected fraud: call 1-800-MEDICARE or report to the HHS Office of Inspector General at oig.hhs.gov/fraud. Never simply pay a bill that doesn't match your records without verifying it first.
Is the EOB the same as a bill?
No — an EOB or Medicare Summary Notice is not a bill. It shows you how a claim was processed. You should not pay based on an EOB alone. Wait for an actual bill from your provider that matches the EOB. If you receive a bill that is higher than the amount shown as your responsibility on the EOB, contact your provider's billing department before paying.
Medicare billing errors affect an estimated 3–10% of all claims — costing seniors and Medicare billions annually. Most seniors either don't read their EOB or don't know how to interpret it. Understanding this document takes 10 minutes to learn and can protect you from overpaying or missing fraud that could compromise your Medicare benefits.
Two Types: MSN vs EOB
Original Medicare (Parts A and B): Your document is called the Medicare Summary Notice (MSN). It arrives quarterly by mail and covers all claims processed in that 3-month period. Access current claims faster at MyMedicare.gov.
Medicare Advantage (Part C): Your document is called an Explanation of Benefits (EOB). It typically arrives after each claim or monthly, from your specific insurance company — not from Medicare directly.
How to Read Your MSN/EOB
Every Medicare MSN or EOB contains the same basic information in similar formats:
| Column/Field | What It Means | What to Check |
|---|---|---|
| Date of service | When the service was provided | Matches your actual visit date? |
| Provider name | Who billed Medicare | Recognize this provider? |
| Amount billed | What the provider charged | Often higher than Medicare allows |
| Medicare approved | What Medicare agreed the service is worth | The actual value used for payment |
| Medicare paid | What Medicare actually sent to the provider | Usually 80% of approved amount |
| You may be billed | Your estimated responsibility | Should match actual bill — flag any discrepancy |
Red Flags to Check Every MSN/EOB
- Services you don't recognize: Any date, provider, or service that doesn't match your records is potentially fraudulent. Even small amounts matter — Medicare fraud often starts with small test charges
- Duplicate entries: The same service, same date, same provider appearing twice on the same document
- Services on dates you didn't receive care: Especially important if you were traveling or hospitalized elsewhere on that date
- Equipment you didn't order: Durable medical equipment (wheelchairs, CPAP supplies, diabetic supplies) that you didn't request or receive
- Lab tests without a doctor's order: Tests billed without a corresponding physician visit or order
What to Do When You Find an Error
- Write down the claim details — date, provider, service, amount
- Call the provider's billing department first — many errors are coding mistakes that can be corrected without a formal appeal
- If unresolved, call 1-800-MEDICARE and report the discrepancy
- For Original Medicare: file a Redetermination appeal within 120 days of the MSN
- For suspected fraud: report to the HHS OIG at oig.hhs.gov or 1-800-HHS-TIPS
- Read every MSN/EOB when it arrives — don't file it unread
- Check every date and provider against your own appointment records
- Never pay a provider bill higher than your EOB shows as your responsibility without questioning it
- Sign up for MyMedicare.gov — view claims faster, flag suspicious entries online
- Report anything suspicious — Medicare fraud drives up costs for everyone
→ How to Appeal a Medicare Claim Denial
→ Protect Yourself from Medicare Fraud
→ Medicare Summary Notice — Deep Dive