CO-20: injury covered by a liability carrier.

What X12 says CARC 20 means

This injury/illness is covered by the liability carrier.

CARC 20 · Start 01/01/1995, last modified 09/30/2007.

In plain terms: The injury or illness is covered by a liability carrier.

What it means on a remittance

The payer is saying that another party’s liability coverage, such as a property or auto liability policy, is responsible for the injury. CARC 19 is the sibling code for workers’ compensation and CARC 21 for a no-fault carrier.

Typical causes

• The patient was injured in an accident the claim marks as someone else’s fault.
• The accident indicator on the claim says other accident or auto accident.
• The payer’s file shows an open liability or subrogation case.
• The diagnosis is an injury code that the payer screens for third-party liability.

These are common billing patterns, not a diagnosis of your claim. The remittance and the payer's policy decide.

What to check

1. Ask the patient how the injury happened and whether another party is involved.
2. Get the liability carrier, claim number and date of loss if there is one.
3. Check the accident indicators on your claim.
4. Ask the payer whether it will pay conditionally while liability is decided.

Correct, resubmit or appeal

If a liability carrier is involved, bill it or follow your policy for liability cases, and keep the payer informed. If no one else is liable, correct the claim indicators and ask the payer to reprocess.

Medicare dates that apply

A Medicare redetermination request must be filed within 120 calendar days from the date a party receives the notice of the initial determination; receipt is presumed 5 calendar days after the notice date unless there is evidence to the contrary (42 CFR 405.942(a)), and a late request can be considered for good cause (405.942(b)). Other payers set their own appeal windows in the contract or plan documents, so read the notice for the date. The tool above runs the date math.

Related codes

X12 does not publish a table that pairs each code with remark codes; the payer picks the remark code and prints it beside the CARC on the same remittance line.

Other codes: CARC 19 (workers’ compensation), CARC 22 (may be covered by another payer) and the full lookup.

Worked example (hypothetical)

An ankle fracture claim denies with CO-20. The patient says another driver hit his car. The biller records the other driver’s carrier and claim number and follows the practice’s policy for accident cases.

Sources

• X12: Claim Adjustment Reason Codes — code text, usage notes and dates (list dated 10/30/2026, retrieved 2026-11-02)
• 42 CFR 405.942 — eCFR, current through 2026-10-29 (retrieved 2026-11-02)

Code descriptions are X12 copyrighted material, quoted here only for the codes on this page and linked to the owner. For the full lists, use X12. The X12 text and the Medicare rule above were read from these pages on November 2, 2026. Causes, checks and examples are general billing practice written for this page, not X12 content. Payers revise code lists, contracts and policies, so confirm anything that affects a claim or a deadline with the payer.