Why Health Insurance Claims Surprise So Many People

Most people assume that having health insurance means their medical bills are largely taken care of. Then a claim comes back with an unexpected balance — and suddenly terms like coinsurance, out-of-network, and prior authorization feel a lot more important than they did at enrollment.

These surprises rarely happen because policyholders were careless. They happen because health insurance documents are dense, terminology is inconsistent across plans, and the moments when details matter most — during a medical event — are precisely when no one wants to read fine print. Understanding where the common pitfalls sit makes it far easier to avoid them.

The mistakes below represent the situations that most frequently catch policyholders off guard when a claim is filed. For a broader look at how coverage gaps work across policy types, see our piece on coverage gaps that catch policyholders off guard.

1

Assuming any provider inside an in-network hospital is also in-network.

Why it happens: Patients correctly verify that their hospital is in-network but don't realize that anesthesiologists, radiologists, and other specialists who work there may contract separately and hold different network status.

How to avoid: Before a scheduled procedure, ask the facility to identify every provider who will be involved in your care and confirm their network status directly with your insurer. For more detail on how this works, see common misconceptions about in-network and out-of-network coverage.
2

Skipping prior authorization because the procedure seemed routine or the doctor ordered it.

Why it happens: Patients reasonably trust that a physician's order is sufficient authorization. In many plans, it is not — the insurer must separately approve certain services before they are rendered.

How to avoid: Call the member services number on your insurance card before any scheduled imaging, surgery, specialist visit, or prescription that might require approval. Ask specifically whether a prior authorization is required and get a reference number confirming it was granted.
3

Believing that hitting the deductible means the plan pays 100% from that point forward.

Why it happens: The deductible is often described as the threshold after which insurance 'kicks in,' which implies full coverage. Most plans actually require the member to continue paying a percentage — called coinsurance — until the out-of-pocket maximum is reached.

How to avoid: Locate your plan's coinsurance percentage and out-of-pocket maximum in your Summary of Benefits and Coverage document. These two numbers together define your true maximum exposure for a given plan year.
4

Missing a timely filing deadline for claim submission.

Why it happens: When a provider bills the insurer directly, patients assume the submission is handled. If the provider fails to bill within the plan's deadline — often 90 to 180 days — the claim can be denied entirely, and the patient may still owe the balance.

How to avoid: After any significant service, follow up with both your provider and your insurer within 30 days to confirm the claim has been submitted and received. Don't wait for a bill to arrive as your only signal.
5

Accepting a claim denial without appealing it.

Why it happens: Denial letters often use technical language that feels final. Many policyholders assume the insurer's decision is authoritative and that challenging it is futile or complicated.

How to avoid: Under federal law, you have the right to an internal appeal and, in most cases, an external review. Deadlines to appeal are strict — typically 180 days from the denial notice — so act promptly. Keep copies of all correspondence and request a full written explanation of the denial reason.

What to Do When a Claim Goes Wrong

A denial or an unexpectedly large bill is not necessarily the end of the road. Every health plan regulated under federal law is required to provide a written explanation for a denial and must offer an internal appeals process. If that process fails, an external review by an independent organization is also available in most cases.

Appeal Deadlines Are Strict — Don't Wait

Most health plans set a deadline of 180 days from the date of a denial notice to file an internal appeal. Missing this window can forfeit your right to challenge the decision entirely. As soon as you receive a denial, note the deadline and begin gathering documentation — medical records, the treating provider's notes, and any relevant clinical guidelines your doctor can reference.

When you receive an Explanation of Benefits (EOB) that doesn't match your expectations, request an itemized bill from the provider and compare each line against what your insurer paid. Billing errors — including duplicate charges and incorrect procedure codes — are more common than most people realize, and many are correctable.

For step-by-step guidance on navigating a denial, see why health insurance claims get rejected and how to respond. And if prior authorization was part of the dispute, how prior authorization works — and what to do when it's denied walks through your options in detail.

1 in 5

Insured adults who received an unexpected medical bill

According to a KFF Health Care Debt Survey, roughly one in five insured adults reported receiving a surprise medical bill from a provider they believed was in-network.

~40%

Appeal overturn rate for denied claims

Data from state insurance regulators consistently shows that a meaningful share of internal appeals result in a full or partial reversal of the original denial, though rates vary by plan and state.

This article is for general informational purposes only and does not constitute personalized insurance, financial, or legal advice. Coverage terms, exclusions, and claim procedures vary by plan and state. Always review your actual policy documents and consult a licensed insurance professional for guidance specific to your situation.