Getting claims paid, and what to do when they are not.
Aetna gives out of network providers 12 months to file medical claims. In network, its provider manual points to your agreement, not a number. Here is what Aetna does publish: Texas and New York rules, the 180 day reconsideration and 60 day appeal clocks, Medicare Advantage, Aetna Better Health by state, and Signature Administrators cards.
Cigna Healthcare gives participating providers 90 days after the date of service to file a claim, and out of network providers 180. Here is how the clock runs for hospital stays and secondary claims, why a corrected claim gets no new clock, the 180 day appeal window, Evernorth behavioral claims, and where Cigna’s Medicare plans went.
CO-253 isn’t a denial. It’s Medicare’s 2 percent sequestration cut, taken from Medicare’s payment after the deductible and coinsurance, so the patient’s share never changes. Here is the math in Medicare’s order, the rate by date of service, why you can’t bill it to the patient, and how Medicare Advantage plans handle it.
Optum Behavioral Health runs two 90 day clocks. Claims must reach Optum within 90 days of the date of service, but corrections run 90 days from the day Optum received the first claim, not from the remittance. Here is how to count both, how to send a correction, what proves a claim was on time, and where California, Medicaid and VA claims differ.
UMR does not publish a timely filing limit, because UMR is not an insurer. It runs claims for employers that fund their own plans, so the employer’s plan and your network contract set the clock. Here is how to find the limit for one plan, what UMR’s own FAQ says about corrected claims and proof, and the 180 day appeal rule for private employer plans.
CO-50 means the payer decided your service was not medically necessary. Unlike a timely filing denial, it can often be argued, but only once you find the policy the payer used. Here is how to read the group and remark codes, when an ABN moves the cost to the patient, what Medicare Advantage plans may not do, and what an appeal needs.
Most sites say UnitedHealthcare gives you 90 days to file. Its own 2026 guide sends you to your contract instead, and the 90 days on its website is an example. What UHC does publish is which clock each plan runs, and a corrected claim can be late on one of those clocks while it would be on time on another. Here is each one, quoted from UHC, Optum and UMR.
CO-29 means the payer says your claim arrived after its filing limit. From Original Medicare, that denial is not subject to appeal at all, and only four narrow exceptions reopen the door. From every other payer, it is won or lost on dates and proof. Here is how to tell which kind you have before anyone writes an appeal.
Most practices believe they can prove when a claim was filed. Then a CO-29 arrives, they pull the file, and the document they kept turns out to prove something else. A 999 acknowledgment confirms your clearinghouse received your file. Only a 277CA confirms the payer received your claim, and only the second one wins an appeal. Plus why a rejected claim never stopped the clock.
CO-97 means the payer decided one of your codes was already paid for inside another. Before writing an appeal, look up the modifier indicator on that code pair. If it is 0, no modifier and no documentation will ever unbundle it, and repeated override attempts are exactly the pattern audit selection looks for. Here is how to tell an appealable denial from a correct one in under a minute.
Most billers read a remittance from the top down and post what they see. That works until the deposit does not match what the remittance said you were paid. When that happens the money is almost always in a segment near the bottom that nobody reads. Here is where provider level adjustments hide, why forward balances are so hard to trace, and a ten minute reconciliation that catches them.
CO-45 means your billed charge exceeded the allowed amount, and the difference is a contractual write-off. It is almost never an error and rarely worth appealing. What matters is what you do with the difference, because billing the patient for it is balance billing. Here is how to tell a normal write-off from a genuine underpayment.