Health insurance claims work like this: when you get medical care, your provider sends a bill to your insurer with codes describing what was done and why, the insurer checks it against your policy, and then pays the provider directly after subtracting whatever you owe in cost-sharing. You usually never touch the paperwork. You find out how it turned out from an Explanation of Benefits that arrives after the fact. The process only becomes your problem when a claim is denied, when you see an out-of-network provider, or when you pay upfront and have to seek reimbursement yourself.
The Path a Claim Takes
After an in-network visit, the provider’s billing office submits a claim electronically. The insurer reviews it against your policy: were you covered on the date of service, is the provider in network, did the service need prior authorization, and do the diagnosis and procedure codes match a covered benefit. If everything lines up, the insurer pays the provider directly, minus your cost-sharing, and sends you an Explanation of Benefits.
If something doesn’t line up, the claim is rejected or denied, and that’s when you hear about it. The two words are not identical. A rejection usually means a technical problem (a wrong code, a missing field) that the provider can correct and resubmit. A denial is a decision on the merits that the service isn’t covered or wasn’t necessary, which you have the right to appeal.
What You Actually Owe on a Claim
Every plan has a cost-sharing structure that splits the bill between you and your insurer. Four terms do most of the work:
- Deductible: the amount you pay out of pocket before your insurer starts covering costs. A $1,500 deductible means you pay the first $1,500 of covered services each year.
- Copayment: a flat fee for specific services, like $30 for an office visit or $200 for an emergency room visit.
- Coinsurance: your percentage share after you meet the deductible. If the plan covers 80%, your coinsurance is 20%.
- Out-of-pocket maximum: the ceiling on what you can be required to pay in a plan year. For 2026, the federal cap is $10,150 for individual coverage and $20,300 for family coverage. Once you hit it, the plan covers 100% of remaining covered services.
Network status changes the math significantly. In-network providers have negotiated rates with your insurer, so you pay less. Out-of-network providers set their own prices, and your plan either covers a smaller percentage or nothing. Many plans run separate deductibles and out-of-pocket limits for out-of-network care, so your in-network spending doesn’t count toward your out-of-network cap.
Plans also differ on referrals and prior authorization. HMO plans generally require a referral from your primary care doctor before you see a specialist. PPO and EPO plans usually let you see specialists directly but may still require prior authorization for expensive services like MRIs, non-emergency surgeries, or extended physical therapy. A claim submitted without a required authorization is routinely denied.
One category sits outside this structure. Under the Affordable Care Act, most plans must cover certain preventive services at no cost when you use an in-network provider: no copay, no coinsurance, and the service doesn’t count against your deductible. Routine immunizations, cancer screenings, blood pressure and cholesterol checks, contraception, and tobacco cessation programs all qualify.1HealthCare.gov. Preventive Health Services If a preventive visit turns into treatment because the doctor finds and addresses a problem on the spot, the treatment portion can generate a separate claim with standard cost-sharing. Preventive services are also commonly miscoded, so a bill for what should have been a free screening is worth questioning before you pay.
When You File the Claim Yourself
You may need to submit a claim directly when you see an out-of-network provider or pay upfront. Deadlines vary. Some insurers give 90 days from the date of service, others 180 days or more. Medicare allows a full 12 months. Missing the deadline can result in denial even when the service would otherwise have been covered, so check your plan’s specific rule before you file.
Two documents form the core of the submission: an itemized bill and a completed claim form. The itemized bill needs the provider’s name, the date of service, a description of each service, procedure codes, charges, and the provider’s National Provider Identifier, a 10-digit number assigned to every healthcare provider that insurers use to verify who delivered the care.2Centers for Medicare & Medicaid Services. The Who, What, When, Why and How of NPI The claim form is typically the CMS-1500 for outpatient and professional services or the UB-04 for hospital and facility claims.3Centers for Medicare & Medicaid Services. CMS 1500 Your insurer’s website usually has a downloadable version.
For surgery, ongoing therapy, or high-cost treatments, the insurer may also want supporting medical records, physician notes, test results, or pre-authorization letters. Keep copies of everything, and get confirmation that the insurer received the submission. A claim that gets lost is functionally a denied claim until you prove otherwise.
Reading Your Explanation of Benefits
Once a claim is processed, you receive an Explanation of Benefits. It is not a bill. It tells you what the provider charged, what the insurer agreed to pay, and what you owe.4Centers for Medicare & Medicaid Services. How to Read an Explanation of Benefits
Four lines matter most: provider charges (what was billed), allowed charges (the negotiated rate your insurer will pay against), the amount the insurer paid, and the patient balance. The bill you get from the provider should not exceed the patient balance on the EOB. If it does, call the provider’s billing office, because something is off. The EOB also carries remark codes, short alphanumeric codes explaining adjustments or denials, with descriptions at the bottom of the document. When a claim is partially paid or denied, those codes are your first clue about what happened.
Protection From Surprise Bills
The No Surprises Act, in effect since 2022, protects you from balance billing in three situations: emergency services at any facility, non-emergency services from out-of-network providers at in-network hospitals and ambulatory surgical centers, and out-of-network air ambulance services.5U.S. Department of Labor. Avoid Surprise Healthcare Expenses – How the No Surprises Act Can Protect You
When the protections apply, your plan can’t charge you more in cost-sharing than it would for the same service from an in-network provider, and the amount counts toward your in-network deductible and out-of-pocket maximum.6Office of the Law Revision Counsel. 42 US Code 300gg-111 – Preventing Surprise Medical Bills Out-of-network providers can’t balance bill you for ancillary services like anesthesiology, pathology, and radiology done during a visit to an in-network facility, and they can’t ask you to waive these protections for those services.
The protections don’t apply everywhere. If you voluntarily go to an out-of-network facility for non-emergency care, the law doesn’t cover you. It also doesn’t apply to short-term insurance plans, standalone dental or vision plans, or retiree-only plans. For scheduled non-emergency care with an out-of-network provider at an in-network facility, the provider can ask you to consent to waiving the protections, but only with written notice at least 72 hours before the service that includes a good-faith cost estimate and information about in-network alternatives.
Why Claims Get Denied
Denials fall into a handful of categories, and the category determines what you can do about it.
- Coding errors. Mismatched diagnosis and procedure codes are the most common cause of preventable denials. If the ICD diagnosis code doesn’t support the CPT procedure code, the insurer’s system flags the claim. The provider’s billing department can usually fix this by resubmitting with corrected codes.
- Missing prior authorization. Services that needed pre-approval but were performed without it get denied almost automatically. Some denials can be reversed if your doctor can show the treatment was urgent, but the success rate drops after the fact.
- Out-of-network provider. The claim pays less or not at all. Check the EOB to see whether No Surprises Act protections should have applied.
- Not medically necessary. The insurer decides the service wasn’t required for your condition. These are the disputes that most often reach appeal.
- Administrative errors. Wrong date of birth, transposed policy number, misspelled name. The easiest to fix, usually with a corrected resubmission.
Your insurer must tell you why the claim was denied, either in the EOB or a formal denial letter. That reason is where any response starts. Simple errors get fixed by phone with the provider’s billing office. Coverage disputes and medical necessity decisions require an appeal.
How To Appeal a Denial
Federal law gives you a two-stage appeal: an internal appeal handled by the insurer, and an external review handled by an independent third party.7HealthCare.gov. How to Appeal an Insurance Company Decision
Internal Appeal
You have 180 days from the denial notice to file.8HealthCare.gov. Internal Appeals Submit the insurer’s appeal form (or a letter with your name, claim number, and insurance ID), plus supporting evidence: medical records, a letter from your doctor explaining why the treatment was necessary, corrected billing codes, or test results. A representative, including your doctor, can file on your behalf.
For employer-sponsored plans governed by ERISA, federal regulations set deadlines the plan must meet. Urgent care appeals must be decided within 72 hours. Pre-service appeals get 30 days. Post-service appeals get 60 days.9eCFR. 29 CFR 2560.503-1 – Claims Procedure If the plan takes an extension, it has to tell you why.
External Review
If the internal appeal fails, you can request an external review within four months of the final internal denial. An independent reviewer not affiliated with your insurer evaluates the case and issues a binding decision. Standard reviews must be completed within 45 days; urgent reviews within 72 hours.10HealthCare.gov. External Review Costs to you are either nothing or no more than $25, depending on whether your state runs its own review program. All non-grandfathered health plans must comply.11eCFR. 45 CFR 147.136 – Internal Claims and Appeals and External Review Processes External review is where disputes over medical necessity and whether a treatment is experimental most often get resolved, because the insurer no longer controls the outcome.
When Two Plans Cover You
If you’re covered under two plans, coordination of benefits decides which pays first. The primary plan processes the claim as if it were your only coverage. The secondary plan then picks up some or all of the remaining balance, up to its own limits.
Common rules follow the NAIC model most states have adopted. Your own employer plan is primary over any plan that covers you as a dependent. An active-employee plan is primary over a retiree plan. For children covered under both parents’ plans, the birthday rule applies: the parent whose birthday falls earlier in the calendar year has the primary plan, regardless of which parent is older. If parents are divorced and a court order assigns coverage responsibility, that parent’s plan is primary.
When Medicare is involved, the answer depends on the employer’s size and the employee’s status. Active employee (or the spouse of one) at a company with 20 or more employees: the employer plan is generally primary and Medicare secondary. Retired, on COBRA, or at an employer with fewer than 20 employees: Medicare typically pays first.
Coordination errors stall claims. If both plans think the other is primary, neither pays. When you add a second plan or go through a life change, update both insurers with accurate coordination information.