The 90-Day AR Cliff — Why Old Claims Stop Getting Paid

In my work running GetMax across platforms like Valant and Tebra, I see practice owners look at their AR aging report and wonder why charges above 90 days rarely move. The reason is structural. In medical billing, claims follow a sharp decaying curve. During the first 30 days, claims sit in normal adjudication. Between 31 and 60 days, initial clearinghouse rejections and simple demographic errors occur. By day 60 to 90, if a biller has not touched the claim, it falls into a danger zone where resolution times double.

When a claim crosses 90 days, payers apply heightened scrutiny and automated rules to reject aged submissions. Commercial plans like Aetna, Cigna, or local Blue Cross affiliates frequently set contractual filing windows at 90 or 180 days from the date of service. Once you cross that threshold without a valid initial electronic acceptance on record, the payer issues a CARC CO-29 denial, indicating the time limit for filing has expired.

Code CO-29 carries a Contractual Obligation prefix. That prefix means the write-off is absorbed entirely by your practice. You cannot balance bill the patient, and you cannot re-bill the claim without hard electronic proof of timely submission. When billers see CO-29, they often set the claim aside because appealing it requires manual log extraction, causing old AR to pile up indefinitely.

The most common reason claims hit the timely filing limit is a failure to distinguish between a clearinghouse rejection and an actual payer denial. A rejection happens at the clearinghouse stage before the claim ever reaches the payer's adjudication system. If your front desk enters an invalid subscriber ID or incorrect payer ID, the clearinghouse rejects the claim file in an EDI 277 report.

If your billing team does not clear that rejection queue weekly, the claim sits invisible. The provider thinks the claim was billed on time, but the payer never received it. By the time someone notices the unpaid balance on an AR aging report at day 105, submitting the corrected claim yields an immediate CO-29 contractual adjustment. Another frequent trigger is mismanaged coordination of benefits under code CO-22. A patient presents primary insurance that was retroactively terminated, and by the time the secondary payer is billed four months later, the