Published 2026-09-16 · Last updated 2026-09-16.
How a claim works
A health insurance claim is a formal request to your insurer to pay for care you received. In most in-network visits, your provider files the claim for you: you show your card, pay any copay due at the visit, and the provider sends the claim electronically. You generally do not file anything yourself unless you used out-of-network care or paid upfront and seek reimbursement.
After filing, the insurer processes — or adjudicates — the claim against your plan terms: was the provider in network, was any required prior authorisation obtained, is the service covered, and what cost-sharing applies. That processing produces the document that matters most to you, the Explanation of Benefits.
Reading your Explanation of Benefits
An Explanation of Benefits, or EOB, is not a bill. It is the insurer's summary of how the claim was processed: what the provider charged, what amount was allowed under the plan, what the insurer paid, and what you may owe. The actual bill comes separately from the provider, and it should not exceed the patient-responsibility figure on the EOB.
Compare the two side by side before you pay. If the provider's bill is higher than the EOB's patient-responsibility figure, contact the provider before paying — the difference is often a billing error, a claim still being processed, or a charge that should have been adjusted. Paying first and disputing later is harder than pausing first.
What to keep
Keep the EOB, the provider bill, any prior-authorisation approval, and notes of calls — dates, names and reference numbers — for every significant claim. Keep them until the bill is settled and the EOB and bill agree, and longer for ongoing treatment. That file is your evidence if a denial, duplicate charge or coding error appears later.
Also keep an itemised bill for larger claims and check it line by line: duplicate charges, services you did not receive, wrong quantities and coding errors are the common faults, and they are far easier to spot on an itemised bill than on a summary.
If a claim is denied — general steps
A denial is not final. Read the denial letter and EOB for the exact reason — missing prior authorisation, a service judged not medically necessary, an exclusion, a coding error, or out-of-network care — because the reason decides the fix. Gather the evidence that answers that reason: a corrected code, a prior-authorisation record, or a letter from your doctor explaining medical necessity.
File an internal appeal with the insurer within the deadline stated in your denial notice, in writing, with that evidence attached. If the internal appeal is upheld against you, you generally have a right to an independent external review, whose decision the insurer must follow. Medicare has its own multi-level appeal track, starting with redetermination, so follow the Medicare track rather than the commercial track for Medicare claims.
Preventing the next denial
Most denials are preventable at the front end: confirm prior authorisation before a procedure or scan, confirm network status before a referral, and confirm that a medicine is on formulary before filling it. Those three checks take minutes and prevent the most common denial reasons outright.
When a denial does happen, treat it as a process with a deadline, not as a verdict. Calendar the appeal deadline the day the denial arrives, submit in writing, and keep copies of everything. A calm, evidenced appeal beats an angry phone call, and a significant share of appeals succeed precisely because the first decision rested on incomplete information.
ILLUSTRATIVE EXAMPLE
ILLUSTRATIVE EXAMPLE (not a policy fact): Maya, a fictional patient, receives an EOB showing a patient-responsibility figure lower than her provider's bill. She pauses, compares the two line by line in the example, finds a duplicate charge on the itemised bill, and contacts the provider before paying. The provider corrects the bill to match the EOB. No charge, allowed amount or deadline in this example is asserted as a fact.