The billed amount exceeded the payer's fee schedule or contracted maximum. Payment was reduced to the allowed amount. CO-45 is usually a standard contractual write-off, not an error. The exception: when the allowed amount doesn't match your contract. Multi-location groups with separate TINs are especially vulnerable because each TIN may carry different contracted rates for the same CPT code with the same payer.
CO-45: "Charge exceeds fee schedule/maximum allowable or contracted/legislated fee arrangement."
Most CO-45 adjustments are correct. Practices bill at their full fee schedule rate, which is intentionally higher than any payer's allowed amount.
The payer reduces the charge to their contracted rate and reports the reduction as CO-45. The difference is a contractual write-off that cannot be billed to the patient.
A practice billing $200 for a 99214 and receiving $138 from Medicare sees a CO-45 adjustment of $62. That $62 is the expected gap between the billed charge and the Medicare allowed amount. No action needed.
The problems start when the allowed amount itself is wrong.
Medicare and commercial payers update fee schedules annually, sometimes quarterly. When a payer's system applies last year's rates to current claims, the allowed amount is lower than it should be.
The CO-45 adjustment appears normal because it's still a reduction to "allowed amount." The error hides inside what looks like a routine adjustment.
According to MGMA data, fee schedule lag errors affect approximately 2-3% of claims in the first quarter of each calendar year. For a practice billing $200K/month, that's $4,000-$6,000/month in potential underpayments during Q1 alone.
Medicare rates vary by Geographic Practice Cost Index (GPCI). Commercial payers also adjust rates by region. A claim processed under the wrong locality code pays at the wrong rate. This is particularly relevant for multi-location groups where different offices fall in different GPCI zones. A satellite office 30 miles from the main location may be in a different payment locality.
The Medicare fee schedule has two rates for every CPT code: facility and non-facility. Non-facility rates are 15-40% higher because the practice absorbs overhead that a hospital would otherwise cover. When a payer applies the facility rate to a service performed in a physician office (Place of Service 11), every claim is underpaid by the full facility/non-facility differential.
Commercial payer contracts specify exact rates or a percentage of Medicare. After a contract renewal, the new rates must be loaded into the payer's claims processing system.
Delays in loading create a window where claims process at old rates. The CO-45 adjustment looks routine, but the allowed amount is wrong.
Multi-location risk: Groups operating under multiple TINs frequently have different contracted rates for each TIN with the same payer. A rate negotiated in 2024 for TIN A may be 8% lower than the rate negotiated in 2025 for TIN B. When analyzing CO-45 adjustments, compare allowed amounts by TIN and by location, not just by CPT code. Discrepancies between locations for the same service and same payer indicate a contract loading error or an unfavorable legacy rate that should be renegotiated.
For Medicare: look up the CPT code in the 2026 Medicare fee schedule with the correct locality and facility/non-facility designation. For commercial payers: reference your contract or the payer's fee schedule on their provider portal. The allowed amount on the ERA should match this number within a few cents.
If they match, the CO-45 is correct and the difference is a standard contractual write-off. If they don't match, calculate the variance.
A $2-$3 gap may be rounding. Anything larger warrants investigation.
Verify that POS 11 (office) was on the claim if the service was performed in your office. A claim submitted with POS 22 (outpatient hospital) will pay at the lower facility rate. This is one of the most common causes of CO-45 underpayments and one of the easiest to fix.
Pull the allowed amount for your top 10 CPT codes at each location for the same payer. If Location A receives $138 for 99214 and Location B receives $125, the rates differ by TIN.
Determine whether this reflects a genuine contract difference or a loading error. Legacy rates should be flagged for renegotiation at the next contract renewal.
Payment disputes for CO-45 underpayments require the ERA showing the incorrect allowed amount, the correct rate from your contract or the applicable fee schedule, and the calculated underpayment per claim. Most payers have a separate dispute process for payment variances that differs from the clinical appeal process. Reference the contract effective date and specific rate schedule in the dispute.
Three adjustment codes relate to payment reductions. Each has a different cause and a different fix:
| Code | What It Means | Root Cause |
|---|---|---|
| CO-45 | Charge exceeds fee schedule maximum | Billed amount is higher than the payer's allowed amount. Usually a standard contractual write-off. Underpayment when the allowed amount itself is wrong. |
| CO-97 | Payment adjusted based on procedure rules | NCCI bundling, multiple procedure reductions, or component billing adjustments reduced the payment. The allowed amount may be correct but the payment was reduced by a secondary rule. |
| CO-131 | Claim-specific negotiated discount or contractual adjustment | The contract rate itself was applied incorrectly. The payer used the wrong rate, wrong percentage, or wrong fee schedule version. |
CO-45 is about the ceiling (maximum allowable). CO-97 is about procedure interaction rules. CO-131 is about the contract terms. All three can result in underpayment. A thorough payment audit checks for all three.
Verify fee schedule updates in January. Compare Q1 payments against the new fee schedule for your top 20 CPT codes. Catch lag errors before they compound across hundreds of claims.
Confirm POS codes on every claim. Office services get POS 11. Outpatient hospital gets POS 22. Telehealth from patient's home gets POS 10. A single POS error on a batch of claims can cost thousands before anyone notices.
Audit contracted rates at each contract renewal. When a commercial contract renews, verify that the new rates are loaded correctly by comparing the first payment under the new contract against the new rate schedule. Don't assume the payer loaded the update correctly.
For multi-location groups: standardize rate monitoring across TINs. Build a rate comparison report that shows the allowed amount for your top 10 CPT codes by TIN, by payer, by month. Discrepancies surface immediately in a standardized report. Without it, underpayments at one location hide behind overall revenue averages.
Revenue impact: Most CO-45 adjustments are legitimate contractual write-offs. The underpayment subset is small but high-value: fee schedule errors and POS code errors typically affect $40-$80 per claim across every claim for the affected CPT code. A 99214 POS error running for 3 months at 200 claims/month is a $24,000-$48,000 underpayment. Monthly payment auditing catches these within 30 days.
Our system audits every payment against your contracted rates by TIN, by location, and by payer. Underpayments get flagged before they compound.
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