Denial Code CO-45: Charge Exceeds Fee Schedule Maximum

Denial code CO-45 is technically not a denial at all. It is a contractual adjustment that appears on virtually every remittance advice. When you see CO-45, it means the payer processed your claim, compared your billed charge to their fee schedule or contracted allowed amount, and paid the lower figure. The difference between what you billed and what they allowed is the CO-45 adjustment, and you write it off as a contractual obligation.

Every practice sees CO-45 on most claims. It is a normal part of the reimbursement cycle when your fee schedule is higher than payer allowed amounts, which it should be. The reason billing teams need to understand CO-45 is not to eliminate it but to verify that the allowed amount matches the contracted rate. When it does not, you have a potential underpayment that is worth investigating.

How CO-45 Works

CARC code CO-45 reads: “Charge exceeds fee schedule/maximum allowable or contracted/legislated fee arrangement.” When your practice bills $225 for a 99214 E/M visit and the payer’s allowed amount is $135, the payer pays $135 (minus any patient cost-sharing) and applies a CO-45 adjustment of $90. That $90 is the contractual write-off your practice agreed to when signing the provider contract.

The CO group code confirms this is a contractual obligation. You cannot bill the patient for the $90 difference. Your contract with the payer stipulates that you accept the allowed amount as payment in full for covered services. Patient responsibility is limited to copayments, coinsurance, and deductible amounts as defined by their plan.

CO-45 often appears alongside other adjustment codes on the same claim line. You might see CO-45 for the contractual adjustment, PR-1 for the patient deductible portion, and PR-2 for the patient coinsurance portion. Together, these codes account for the entire billed amount: payer payment + CO-45 write-off + patient responsibility = total billed charge.

Why Your Fee Schedule Should Always Exceed Payer Rates

New practices sometimes set their fee schedule close to Medicare rates to appear affordable. This is a costly mistake. Payers pay the lower of your billed charge or their allowed amount. If your fee schedule is $100 and the payer allows $120, you receive $100. You just left $20 on the table.

The standard recommendation is to set your fee schedule at 150% to 250% of Medicare rates. This ensures that your billed charges exceed the allowed amount for every payer in your mix. You will see larger CO-45 adjustments, but your actual payments will be maximized. The CO-45 write-off is not real revenue loss because you were never going to collect more than the allowed amount.

Review your fee schedule annually against updated Medicare rates and commercial payer fee schedules. When Medicare increases rates (as they did for E/M codes in recent years), your commercial payer allowed amounts may follow. If your fee schedule has not kept pace, you could be under-billing relative to what payers are willing to pay.

When CO-45 Signals an Underpayment

The critical question with CO-45 is not “why did the payer adjust my charge?” but “did the payer pay the correct allowed amount?” Your provider contract specifies a fee schedule, often as a percentage of Medicare, a flat rate per CPT code, or a reference to the payer’s published fee schedule. When the paid amount is less than the contracted rate, you have an underpayment regardless of the CO-45 adjustment.

Underpayments happen more frequently than most practices realize. A 2023 industry study found that 7% to 11% of commercial payer claims had payment variances below the contracted rate. Common causes include payer fee schedule loading errors after contract renewals, incorrect geographic locality assignments, failure to apply negotiated rate increases, and miscategorization of procedure codes to the wrong fee schedule tier.

To catch underpayments, compare the paid amount for each CPT code to your contracted rate. Most practice management systems can run a payment variance report that flags claims where the paid amount deviates from the expected amount by more than a set threshold. Reviewing this report monthly catches systematic underpayments before they accumulate.

Fee Schedule Negotiation and CO-45

Understanding your CO-45 patterns gives you data for fee schedule negotiations. When a contract comes up for renewal, pull a report showing your top 25 CPT codes by volume, the current allowed amount for each, and the gap between your billed charges and allowed amounts. This shows the payer exactly how much you write off on their patients and strengthens your position when requesting rate increases.

Focus negotiations on high-volume, high-value codes where even small rate increases generate meaningful revenue. A $5 increase on a code you bill 500 times per year adds $2,500 annually. Across your top 10 codes, targeted rate negotiations can add $15,000 to $50,000 in annual revenue for a mid-sized practice.

Some payers offer tiered fee schedules based on quality metrics, patient volume, or value-based care participation. If your practice qualifies for a higher tier, verify that your claims are being paid at the higher rate. Payers sometimes fail to update the fee schedule assignment when a practice moves to a new tier, resulting in CO-45 adjustments based on the lower rate.

Out-of-Network CO-45 Considerations

When you provide services to patients whose insurance you are out of network with, CO-45 takes on different implications. Out-of-network, the payer may apply their “usual and customary” (UCR) rate or a percentage of Medicare as the allowed amount. These amounts are often significantly lower than in-network rates.

State surprise billing laws (including the federal No Surprises Act) limit what out-of-network providers can bill patients in certain situations, particularly emergency services and services at in-network facilities. In these cases, the CO-45 adjustment represents the difference between your charge and the payer’s initial payment, and you may have the right to pursue the independent dispute resolution (IDR) process for a higher payment.

For non-emergency, non-surprise billing situations where you are out of network, the patient may be responsible for the difference between the payer’s allowed amount and your full charge (balance billing). This depends on state law and the specific circumstances of the service. Check your state’s balance billing regulations before billing the patient for amounts beyond the CO-45 adjustment.

Monitoring CO-45 Across Your Practice

Set up a quarterly CO-45 review process. Pull payment data for your top CPT codes by payer and compare paid amounts to contracted rates. Flag any CPT/payer combination where the average paid amount is more than 2% below the contracted rate. Investigate these flagged items by pulling individual claims and remittance advice to determine if the underpayment is systematic.

When you identify a systematic underpayment, contact the payer’s provider relations department with specific claim examples. Provide the claim number, CPT code, contracted rate (with contract section reference), and actual paid amount. Request a retroactive adjustment for underpaid claims and correction of the fee schedule going forward. Payers are obligated to pay the contracted rate, and most will process retroactive corrections when presented with clear documentation.

Track your overall collection rate (payments divided by allowed amounts, not billed charges) to gauge billing efficiency. A collection rate below 95% of allowed amounts suggests either underpayments, missed patient collections, or both. CO-45 adjustments should not affect your collection rate calculation because the adjustment represents amounts you never expected to collect.