Claim adjustment reason code · X12
CARC 50: not medically necessary.
CARC 50 means the payer decided the service did not meet its medical necessity rules. If you will appeal Medicare, the request is due 120 days after the notice is received, and receipt is presumed 5 days after the notice date.
Medicare redetermination deadline
Result
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What X12 says CARC 50 means
These are non-covered services because this is not deemed a 'medical necessity' by the payer.
CARC 50 · Start 01/01/1995, last modified 07/01/2017.
X12 usage note: Refer to the 835 Healthcare Policy Identification Segment (loop 2110 Service Payment Information REF), if present.
Why it happens
Payers attach coverage criteria to procedures: a required diagnosis, a frequency limit, an age range, or a documented clinical indication. When the claim's diagnosis and history do not satisfy those criteria, the line is denied as not medically necessary. The diagnosis pointer on the claim and the remark code on the remittance are the first things to read. Check the diagnosis code is the most specific one the record supports and is pointed to the right line.
The Medicare redetermination clock
Under 42 CFR 405.942(a), a request for redetermination must be filed within 120 calendar days from the date the party receives the notice of initial determination. The date of receipt is presumed to be 5 days after the date of the notice unless there is evidence to the contrary. The request counts as filed on the date the contractor receives it. A late request can be accepted if the party shows good cause. 405.944 adds that the request must be in writing, go to the contractor named on the notice, and include the beneficiary name, Medicare number, the services and dates, and the party's name.
Example: a notice dated October 1, 2026 is presumed received October 6, 2026, and the last day is February 3, 2027. The calculator on this page does that arithmetic. Commercial plans and Medicare Advantage plans set their own appeal deadlines in the denial letter, so read it.
What to gather
- The remittance line, the remark code and the denial letter.
- The clinical notes that show the indication, dates and results the payer's policy asks for.
- The payer's written coverage policy for the code, so you can answer its exact criteria.
- A short cover letter that points to where each criterion is met in the notes.
Who can bill the patient
Whether the patient can be billed for a not-medically-necessary service depends on the group code, the payer contract and, for some programs, a signed advance notice. This page cannot tell you that. Do not bill until the payer or contract confirms it.
Sources
- X12: Claim Adjustment Reason Codes — code text, start and last-modified dates (list dated 10/30/2026, retrieved 2026-11-01)
- eCFR: 42 CFR 405.942 and 405.944 — redetermination time frame and filing requirements (retrieved 2026-11-01)
Every code description and rule above was retrieved from these pages on November 1, 2026. Payers revise code lists, contracts and policies, so confirm anything that affects a claim or a deadline with the payer.
Frequently asked questions
How long do I have to appeal a Medicare medical necessity denial?
120 calendar days from receipt of the initial determination, with receipt presumed 5 days after the notice date, per 42 CFR 405.942(a). Good cause can extend it.
Does CARC 50 apply only to Medicare?
No. It is an X12 code used by all payers. The 120-day rule on this page is Medicare fee-for-service only; other plans use the deadline in their denial letter.
Is CARC 50 the same as CARC 96?
No. CARC 96 is a general non-covered charge and requires a remark code. CARC 50 is specifically about medical necessity.
Not legal, billing or medical advice
This page explains published code lists and rules and runs a lookup in your browser. It cannot see your claim, your contract or any payer's policy. Confirm with the payer or your Medicare Administrative Contractor before you resubmit, appeal or bill a patient.