What Happens to the Other 99 Percent: A Working Guide to Insurance Appeals in 2026

American health plans deny roughly 250 million claims a year, on the working estimates the Commonwealth Fund and KFF have been publishing for the better part of a decade. Less than one percent of those denials get formally appealed. When they do, a meaningful share gets overturned. KFF's analysis of 2023 Medicare Advantage prior-authorization data found that the vast majority of appeals filed were reversed in whole or in part. Most of the gap, in other words, is not a merits problem. It is a deadlines and paperwork problem.

This is a working guide for the patient or caregiver sitting at the kitchen table with a denial letter, not a thesis on health policy. I am going to walk through which legal regime covers your appeal, the deadline you almost certainly have wrong, the four pieces of evidence the carrier's reviewer is actually looking for, and where to ask for help that is free and where to pay for help that is not. Apellica builds appeal letters for a living, so my hand is on the scale. I have tried to flag where.

A note on sources before we start. Everything in here cites primary federal regulation, Federal Register notices, KFF, ProPublica, and the NAIC. Those institutions are cited because they have done the public-interest reporting; they do not endorse Apellica and we do not pretend otherwise.

The four regimes, and why your denial only lives in one

Most patients do not know which set of federal rules governs their appeal, and the deadlines, evidence standards, and external-review rights are not the same across them. There are four regimes that cover almost every commercially or publicly insured American. Get this part wrong and you can file a perfectly reasonable appeal in the wrong place, on the wrong form, citing the wrong rule.

The first is the Affordable Care Act framework, codified at 45 CFR 147.136. It covers ACA Marketplace plans and fully insured employer coverage. The patient has 180 days from the date of denial to file an internal appeal. The plan must respond within 30 days on a pre-service claim, 60 days on a post-service claim, and 72 hours on an urgent-care claim. The reviewer cannot be the same person who issued the denial. If medical judgment is involved, a medical specialist has to look at it. After an internal denial is upheld, the patient gets four months to request external review by a state-approved Independent Review Organization, and the IRO decision binds the carrier.

The second is ERISA, which covers self-funded employer plans. That is roughly 60 percent of insured workers. The governing rule is 29 CFR 2560.503-1. The deadlines mirror the ACA floor. A few details matter. Plan documents, including the Summary Plan Description and the master plan document, must be produced on request within 30 days, with a copy fee capped at 25 cents a page. The appeal gets a "full and fair review," which is the regulation's language for "the reviewer takes a fresh look, not a rubber stamp." After internal appeals are exhausted, the patient can sue under ERISA Section 502(a)(1)(B). The trap that catches most patients here is a denial citing plan language the patient has never seen. The 30-day document-request right is the lever that fixes it.

The third is Medicare Advantage, governed by 42 CFR Part 422, Subpart M. It has five levels. Plan reconsideration is filed within 60 days. If the plan upholds, the case auto-forwards to an Independent Review Entity (a CMS contractor, currently Maximus). After that comes an Administrative Law Judge hearing at the Office of Medicare Hearings and Appeals, which has an amount-in-controversy threshold updated annually by CMS. Then the Medicare Appeals Council. Then federal District Court. Most patients stop at Level 1. They should not. The IRE reverses a meaningful share of cases the plan refused to.

The fourth is Original Medicare Parts A and B, run under 42 CFR Part 405 through Medicare Administrative Contractors. Five levels again. Different forms. Different deadlines. Almost the same shape as Medicare Advantage, and confusingly close enough that patients regularly file the wrong form.

That is the entire universe. If you have insurance and you got denied, your appeal lives in one of those four buckets. The first thing to do with a denial letter is figure out which.

The 180-day clock is wrong

The single most-missed detail in this whole field is the start date on the clock. The 180-day deadline runs from the date printed on the denial letter, not the date you opened the envelope. A denial dated March 1, received March 8, expires on August 28, not September 4. Patients who mail an appeal on day 181 routinely get a procedural rejection that is almost impossible to undo. The clock starts when the carrier dated the letter. Most patients calendar the wrong day.

The Medicare Advantage clock is shorter and meaner: 60 days for the initial reconsideration, set by 42 CFR 422.582. There is a "good cause" extension in the same section. It is granted at the plan's discretion. It is not a deadline you should rely on. OMHA's 2024 workload report flagged late filing as one of the most common procedural reasons cases never reach the merits.

If you remember one thing from this piece, remember the date in the upper right corner of the denial letter and count from that.

Why this is harder than it looks

The denial letter looks like a single decision. It is, in practice, the front edge of a procedural maze the carrier built to its own specifications. Across the commercial and Medicare Advantage market we count more than two hundred carrier-by-denial-type combinations in active use in 2026, and the medical-policy bulletin that controls one of them looks nothing like the bulletin controlling another. Aetna's not-medically-necessary template for a spinal-cord stimulator runs through one criteria set. Anthem's runs through a different one. UnitedHealthcare pulls from MCG. Cigna pulls from InterQual. The patient who writes a generic appeal arguing the merits of her case is arguing against a framework she has not read, applied by a reviewer who has read it a thousand times.

The Administrative Law Judge precedent library that governs Medicare Advantage appeals is the appeal lawyer's working reference. It is not on the carrier's website. The 30-day ERISA document-request right requires a demand letter with the correct CFR citations or the plan administrator will treat it as a courtesy inquiry and stall. Procedural exhaustion missteps, filing the wrong appeal at the wrong level, missing the certified-mail requirement, omitting the regulatory hook, can foreclose a later civil action under ERISA Section 502(a)(1)(B).

Medicare Advantage adds its own clock pressure: 60 days for the initial reconsideration, 72 hours for an expedited request, four hours for the hospital-discharge expedited window. Forms differ between Part A, Part B, and Part C. Fax numbers differ between carriers and between markets within the same carrier. The carrier's reviewer is paid full-time to uphold denials. The patient is exhausted, often ill, and often reading the denial letter for the first time at the kitchen counter at 9 p.m. on a weekday. That asymmetry is the reason the appeal-filing rate is under one percent. The carrier counts on it.

What a winning appeal actually contains

Free-form appeals get read once and routed back. The appeal that gets read carefully has four pieces, in this order, each addressed to a specific reviewer concern. This is the structure our senior reviewers use, and it tracks what other appeal-prep desks and ERISA-specialist firms describe in their own published guidance.

The first piece is the plan-language citation. The reviewer needs to see the provision that supports coverage, not the one that excludes it. Carriers write their summary plan descriptions to enumerate exclusions in detail and benefits in general terms; the appeal that surfaces the benefit clause, by section number, shifts the burden in a way the form-letter response is not built to handle.

The second is the clinical facts, drawn from the patient's actual medical record and aligned to the carrier's own published medical-policy criteria. Not "my doctor thinks this is necessary." A side-by-side of the carrier's criteria and the patient's chart entries, with dates and the names of the criteria documents.

The third is the peer-reviewed evidence stack, formatted to the carrier's evidence framework: PMID, journal, year, level of evidence. The carriers run on evidence hierarchies. If the appeal argues from preference instead of from the same hierarchy, the reviewer has nothing to map it against.

The fourth is the regulatory hook: 45 CFR 147.136(b)) for ACA, 29 CFR 2560.503-1 for ERISA, 42 CFR 422.566 for Medicare Advantage. The hook signals to the reviewer that the appeal is procedurally grounded and that a deviation from the regulation creates exposure for the plan.

None of those four pieces is the kind of thing a patient assembles in a week from a denial letter and a Google search. That is not a sales pitch; it is what the work actually looks like.

What gets reversed, and what is harder

The mix of denial types is reasonably stable across the public datasets KFF, the HHS Office of Inspector General, and individual state insurance regulators have published. Roughly 30 percent of denials are for lack of prior authorization. About a quarter are medical-necessity denials. Step therapy and formulary issues run around 15 percent. Out-of-network sits near 10 percent. Coding errors are another 10 percent. Experimental or investigational denials are about 5 percent.

The reversal rates run roughly in the reverse order of difficulty, for an unromantic reason. Prior-authorization, step-therapy, and coding-error denials reverse at the highest rates when appealed with proper documentation, because the underlying problem is procedural. The plan said no for a reason that does not survive a second look. Medical-necessity denials are harder because you have to build the clinical case from the patient's chart. Experimental or investigational denials are the hardest, because they require challenging the plan's medical-policy framework on its own terms. Even those reverse, when the appeal cites peer-reviewed literature that meets the carrier's own evidence standards.

I am deliberately not giving you a single headline reversal rate. The numbers in the public reporting move year to year, and the denominators are not the same across CMS, KFF, and the state-DOI data. The directional point holds across every dataset I have looked at: the second look is materially more favorable to the patient than the first, and patients who stop after the carrier's internal denial leave a real share of recoverable coverage on the table.

When the internal appeal fails, external review is a different game

Internal appeals are reviewed by the carrier itself, or for ERISA self-funded plans by the plan administrator. External review is a separate process, conducted by an Independent Review Organization with no financial relationship to the carrier. The IRO decision is binding. If the IRO sides with the patient, the carrier must pay.

External-review reversal rates run roughly 40 to 50 percent across categories. That is meaningfully higher than internal-appeal reversal rates at the same carrier, for the obvious reason that the IRO does not have a P&L hooked to the outcome. ProPublica's reporting on external review called it "one of the industry's best-kept secrets." Their phrase. Instructions for requesting external review are often buried, sometimes on page seven of the denial letter.

For ACA plans, request external review through your state's Department of Insurance portal. The HHS-administered federal process covers the small number of states that do not run their own. For ERISA plans, follow the procedure in your Summary Plan Description; most ERISA plans have voluntarily adopted ACA-style external review, which means the rights look similar even though the legal source is different.

Where to ask for help that is free

The denial letter does not list these resources. They exist anyway, and they are free.

State Departments of Insurance run consumer-affairs divisions that can file complaints and put a regulator in touch with the carrier. The NAIC consumer site at content.naic.org/consumer.htm lists every state contact. The CMS Consumer Assistance Program operates in more than 35 states under state administration and provides free advocacy. The Department of Labor's Employee Benefits Security Administration is the right call for ERISA-specific questions. The Medicare Rights Center handles Medicare and Medicare Advantage. The Patient Advocate Foundation assigns free case managers for complex situations and reports having helped 3.8 million patients access care over its history. ERISA-specialist attorneys are the right call once a case has been exhausted at the administrative level and is heading to litigation.

Most patients do not need all of these. Most patients need one, and they do not know which one until they try.

Where Apellica fits

Apellica prepares the evidence-based appeal letter. Disclosure: this is the firm I work for. The patient reviews and approves every word before submission and authorizes carrier communications under a HIPAA-compliant Assignment of Benefits. We are not a law firm. We are not a medical provider. We are not an insurance carrier. We are an independent administrative service that turns a denied claim into a properly documented appeal letter.

The model is $0 upfront and a flat fee on successful recovery. If the appeal does not reverse, the patient owes nothing for the preparation work. We cover all 50 states, all ACA plans, all Medicare Advantage plans, all ERISA self-funded plans, and commercial coverage. A senior reviewer reads every case before it goes out. We do not work on cancer, oncology, or rare-disease cases; those belong with subspecialty advocates who do nothing else.

If you do not want to hire anyone, that is fine, and the free resources above are real. If you want a draft prepared by a desk that has read denial letters across more than two hundred carrier-by-denial-type combinations, that is what we do.

If you are sitting on a denial right now

The next 48 hours after a denial arrives matter more than the next six months. Pull the letter out of the envelope. Find the date in the upper right corner. Calendar 180 days from that date if you have ACA or ERISA coverage, 60 days if you have Medicare Advantage. Request your plan documents in writing; for ERISA the legal hook is the 30-day rule in 29 CFR 2560.503-1, and the request triggers a fee cap of 25 cents per page. Find the medical-policy bulletin the denial cites and read it before you write a word of the appeal. Then build the four-part stack, or ask someone who knows the field to build it for you.

The 99 percent of patients who never appeal are leaving coverage on the table, and they are doing it because the procedural overhead is genuinely too high to take on alone. That last clause is the part the carriers count on. It is also, by the numbers, the easiest part of the process to fix.

About the author

Mark Henderson is a senior reviewer at Apellica, an independent insurance appeal preparation service headquartered at One World Trade Center, New York, NY 10007. Apellica is not a law firm and does not provide legal advice. Coverage across all 50 states. Contact: press@apellica.com, +1 (888) 777-6120.

References

• 45 CFR 147.136. ACA Internal Claims and Appeals and External Review.
• 29 CFR 2560.503-1. ERISA Claims Procedure.
• 42 CFR Part 422, Subpart M. Medicare Advantage Grievances and Appeals.
• 42 CFR Part 405. Original Medicare Appeals.
• NAIC Consumer Information Source. content.naic.org/consumer.htm.
• CMS Consumer Assistance Program. cms.gov/CCIIO.
• Patient Advocate Foundation. patientadvocate.org.
• Department of Labor EBSA. askebsa.dol.gov.
• Medicare Rights Center. medicarerights.org.
• KFF analysis of Medicare Advantage prior-authorization data, 2023 reporting year. kff.org.
• ProPublica, "How to Fight Your Health Insurance Denial With an External Appeal."
• Office of Medicare Hearings and Appeals, FY 2024 Workload Report.