The process
How a denial appeal actually works
A denial is the opening position, not the verdict. Federal rules give you a documented process with hard deadlines on both sides. Here is the whole map.
- 01
Read the denial code, not the letter
The paragraph explaining the denial is marketing. The reason code on your Explanation of Benefits is the actual decision. CO-50 (not medically necessary) is a fight about records; CO-197 (no prior authorization) is a fight about process; CO-B7 or a surprise out-of-network charge is often not your bill at all.
- 02
Internal appeal — the plan reviews itself
Every plan type must give you a window to appeal in writing, and the reviewer cannot be the person who denied you or their subordinate. If medical judgment is involved, the plan has to put a clinician with relevant training on it. This is where a specific, citation-backed letter changes outcomes.
- 03
External review — a stranger decides
After the final internal denial, an independent reviewer who is not paid by your plan decides, and the decision binds the insurer. On Medicare Advantage the plan must forward your case automatically. This stage overturns a meaningful share of denials that the insurer upheld twice.
- 04
Regulator pressure and the No Surprises Act
Missed deadlines, undisclosed criteria, and balance bills for emergency or out-of-network care at in-network facilities are enforcement problems. Copies to your state Department of Insurance or the U.S. Department of Labor make a slow plan fast.
Your deadline depends on your plan type
This is the single most common way people lose an appeal they would have won.
| Plan type | Internal appeal | Next level | Authority |
|---|---|---|---|
| Employer plan — self-funded | 180 days | 120 days after final denial | 29 C.F.R. § 2560.503-1(h)(3)(i) |
| Employer plan — fully insured | 180 days | 120 days after final denial | 29 C.F.R. § 2560.503-1(h)(3)(i) |
| Marketplace / ACA exchange plan | 180 days | 120 days after final denial | 45 C.F.R. § 147.136(b)(3)(ii)(A) |
| Individual / off-exchange state plan | 180 days | 120 days after final denial | 45 C.F.R. § 147.136(b)(3) |
| Medicare Advantage (Part C) | 65 days | Automatic independent review | 42 C.F.R. § 422.582(b) |
| Medicaid managed care | 60 days | 120 days after final denial | 42 C.F.R. § 438.402(c)(2)(ii) |
Denial categories the builder handles
Not medically necessary
CO-50 · CO-55 · CO-57The plan agrees the service is covered but says you didn't need it.
No prior authorization on file
CO-197 · CO-198The plan says approval was required before the service and wasn't obtained.
Experimental / investigational
CO-55The plan calls the treatment unproven.
Surprise bill — emergency or out-of-network at in-network facility
CO-B7 · PR-242Emergency care, air ambulance, or an out-of-network clinician at an in-network hospital.
Out of network (non-emergency)
CO-242 · PR-1The plan paid less or nothing because the provider isn't contracted.
Service excluded / not a covered benefit
CO-96 · CO-204The plan points to a plan exclusion.
Filed too late / untimely
CO-29The plan says the claim or appeal arrived after its deadline.
Coding, bundling, or downcoding
CO-97 · CO-4 · CO-16 · CO-45The plan repriced, bundled, or rejected the codes billed.
Not eligible / no coverage on date of service
CO-27 · CO-31 · CO-26The plan says you weren't covered when the care happened.
Step therapy / formulary exception denied
CO-50 · CO-197The plan wants you to fail a cheaper drug first, or excluded the drug.
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