After any medical visit, your insurer sends an Explanation of Benefits. It is printed with "this is not a bill" somewhere near the top, so most people set it aside. That is a mistake, because the EOB is the only document that shows the full arithmetic of what happened, and it is the tool you use to check the bill that arrives separately from the provider.
The five columns
Every EOB, regardless of insurer, contains the same five figures for each line of service:
- Amount billed. The provider's list price. It is largely a fiction; almost nobody pays it.
- Allowed amount. The negotiated rate between your plan and that provider. This is the real price. The difference between billed and allowed is the network discount, and it is often more than half.
- Plan paid. What your insurer sent to the provider.
- Your responsibility. Deductible, copay, and coinsurance combined.
- Not covered. Anything the plan declined, with a reason code.
Your responsibility plus plan paid should equal the allowed amount. If it does not, something is off and it is worth a phone call.
Match the EOB to the bill
This is the single habit worth building. When a bill arrives from the provider, find the matching EOB and compare the patient responsibility figure on each. They should be identical.
When they are not, the usual cause is that the provider billed you before the claim finished processing. Do not pay a provider bill that exceeds the EOB. Call the provider's billing office, give them the claim number from the EOB, and ask them to rebill after adjudication.
If the EOB has not arrived at all and a bill has, wait. Providers sometimes bill patients while a claim is still pending or after a claim was submitted incorrectly, and paying early makes a refund your problem rather than theirs.
Where the errors actually are
Look for these specifically:
- Wrong network status. An in-network provider processed as out of network. This is common after a practice changes ownership or a physician joins a group, and it can multiply your responsibility several times over.
- Duplicate lines. The same procedure code appearing twice on the same date.
- Preventive care applied to the deductible. Certain preventive services are required to be covered without cost sharing. If your annual physical shows a patient responsibility, check whether a diagnostic code was attached that reclassified it.
- Wrong place of service. An office visit coded as a hospital outpatient visit, which brings a facility fee with it.
- Denials for missing prior authorization. Sometimes the authorization existed and was not attached to the claim. That is a fixable clerical problem, not a coverage decision.
Read the remark codes
Denials and adjustments carry short codes with a legend, usually on the back page. Codes matter because they tell you what kind of problem you have. "Not medically necessary" is a clinical appeal. "Service not covered under this plan" is a benefits question. "Missing information" is usually a provider resubmission and often the easiest to fix.
When to appeal
You have the right to appeal a denial, and the EOB will state the deadline, commonly 180 days. Internal appeals go back to the insurer. If the internal appeal fails, most plans also allow an external review by an independent party, and the EOB or denial letter must tell you how to request it.
Appeals succeed more often than people expect, particularly with the treating physician's support. Ask the office for a letter of medical necessity describing why the service was appropriate, what alternatives were considered, and what happens without it. Attach the EOB and the letter, keep copies of everything, and send it in a way that produces proof of delivery.
Track your accumulators
Each EOB shows year-to-date progress toward your deductible and out-of-pocket maximum. Check these periodically for two reasons. First, they are occasionally wrong, especially mid-year when family members' claims are combining. Second, knowing where you stand changes decisions. If you are $400 from your out-of-pocket maximum in October, an elective procedure you were postponing to January may cost you far less if done in December.
Ask for an itemized bill
The provider's statement usually shows a summary. Request the itemized bill with every procedure code and charge. It is your right and it takes one phone call. Line-item review, checked against the EOB, is where charges for services that never happened turn up, and they do turn up.
Keep it all for a year
Save EOBs and matching bills together for at least a year, or longer if you are in an appeal or you itemize medical deductions on your taxes. A folder or a scanned PDF per visit is enough. When a collections notice appears two years later for a bill you already paid, the EOB and the payment record together resolve it in one call instead of five.