What does denial code CO-45 mean?

CO-45 means the charge exceeds the fee schedule or maximum allowable amount set by the payer. In most cases it is not a true denial — it is the contractual write-off between your billed charge and the payer's allowed amount. Every contracted claim will have a CO-45 adjustment unless you bill exactly at the allowed amount. CO-45 only signals a real problem when the allowed amount is lower than your contract says it should be, which is how underpayments hide in plain sight on your ERAs.

Can I bill the patient for a CO-45 adjustment?

No. CO-45 uses the CO (Contractual Obligation) group code, which means the provider has agreed to write off the amount as a condition of the contract. Balance billing a patient for a CO-45 adjustment is a contract violation that can result in termination from the network and, in some states, civil penalties. The full CO-45 amount must be written off.

When does CO-45 indicate an underpayment?

CO-45 indicates a potential underpayment when the allowed amount on the EOB/ERA is lower than the fee schedule rate listed in your contract addendum for that specific CPT code. For example, if your contract says CPT 99213 allows $95 but the EOB shows $78 allowed with a CO-45 for the $17 difference, you have a recoverable underpayment. Underpayments are especially common after contract renegotiations when payers apply new rates inconsistently, or when providers are credentialed under the wrong fee schedule.

How do I appeal a CO-45 underpayment?

CO-45 underpayments are appealed as reconsideration requests, not traditional medical necessity appeals. You need: (1) the original ERA/EOB showing the allowed amount paid, (2) the relevant page of your contract fee schedule addendum showing the correct contracted rate, (3) the CPT code, date of service, and patient account number, and (4) a cover letter stating the discrepancy and requesting payment of the difference. Submit to the payer's provider relations or claims reconsideration department within the appeal deadline — typically 90 to 180 days from the original payment date.

Does CO-45 apply to Medicare claims?

Yes. On Medicare claims, CO-45 represents the standard contractual adjustment between your billed charge and the Medicare Physician Fee Schedule allowed amount. Medicare CO-45 write-offs are not underpayments — Medicare's fee schedule is set by CMS and is not negotiable. Medicare Advantage plans, however, each negotiate their own rates. CO-45 on a Medicare Advantage claim should be compared against that plan's specific contract rate, not the Medicare Physician Fee Schedule.

CO-45 Denial Code: Charge Exceeds Fee Schedule — How to Fix & Prevent

Q: What is the difference between CO-45 and CO-97?

CO-45 means the charge exceeds the allowable fee schedule — it is always present on contracted claims as the write-off of your markup above the allowed amount. CO-97 means the service is already included in the payment for another service — a bundling denial. CO-45 is about fee schedule limits; CO-97 is about bundling and NCCI edits. They are fundamentally different denial types requiring different remediation workflows.

CO-45 in plain English

CO-45 means your billed charge is higher than the amount the payer has agreed to pay for this service. In a contracted relationship, this is completely normal — it is the difference between what you billed and what you negotiated. You write it off; you cannot bill the patient. The question every billing team must ask on every CO-45: is the allowed amount what my contract actually says? If yes, it is a routine write-off. If no, CO-45 is hiding a recoverable underpayment.

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Do not balance bill the patient for CO-45

CO-45 carries the CO (Contractual Obligation) group code. The write-off is your obligation under your provider agreement. Billing the patient for the difference is a contract violation and, in many states, an illegal balance billing violation. The entire CO-45 amount must be adjusted off.

Step-by-Step Fix

What to do when you see CO-45

The workflow splits into two paths: standard write-off (most claims) and suspected underpayment (a small but financially significant minority).

Confirm the group code is CO

On your ERA or EOB, verify the full code reads CO-45, not PR-45 or OA-45. Group code CO means you absorb it. PR would mean patient responsibility. If it is PR-45, the balance may be billed to the patient — but that is extremely uncommon for this code.
Compare the allowed amount to your contract fee schedule

Pull your signed contract addendum (or your contract management system) for this specific payer. Look up the allowed amount for the exact CPT code billed. Compare it to the allowed amount on the ERA. If they match → routine write-off. If the ERA allowed is lower → potential underpayment; proceed to step 3.
Document the discrepancy

Record: CPT code, date of service, billed amount, ERA allowed amount, contract allowed amount, payer name, NPI, claim number. Calculate the underpayment amount per claim. Group underpayments by CPT code — a systematic pattern (same CPT, same payer, consistently low) is worth more in aggregate than isolated claims.
Submit a reconsideration request (not a standard appeal)

Underpayment recovery is a reconsideration — you are not disputing medical necessity, you are citing a contract discrepancy. Submit to the payer's provider relations or claims reconsideration team. Include: the original ERA, the relevant page of your fee schedule addendum with the correct rate highlighted, and a clear cover letter stating the discrepancy. Use the appeal template below.
Track and escalate if no response

If the payer does not respond within 30–45 days, escalate to your provider relations representative. For systematic underpayments involving significant dollars, consider engaging your state medical association or a healthcare attorney, as contractual underpayment is actionable in most states.

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Run a quarterly CO-45 audit — this is where underpayments hide

Pull every CO-45 adjustment for the quarter, group by payer + CPT code, and calculate average allowed amount per code. Compare to your contract rates. Practices that run this report typically find 1–3% of CO-45 volume involves genuine underpayments. On a $5M practice, that is $50K–$150K/year in recoverable revenue that otherwise disappears silently.

Payer-Specific Behavior

How CO-45 behaves by payer type

Payer Type	What CO-45 means here	Underpayment risk
Medicare (Original/FFS)	Standard write-off to the Medicare Physician Fee Schedule (MPFS). Non-negotiable — set by CMS annually. CO-45 here is always expected and not appealable.	Low — MPFS is fixed; the risk is billing the wrong rate (e.g., missing a geographic adjustment)
Medicare Advantage	Each MA plan negotiates its own contracted rates separately from CMS MPFS. CO-45 must be compared to that plan's specific contract addendum — not the MPFS. Rates vary significantly by plan and region.	Medium–High — MA underpayments are common, especially for specialty services and DME
Medicaid (FFS)	State-set fee schedule — the CO-45 adjustment reflects the difference between billed charge and the state Medicaid rate. Not negotiable for FFS; rates are published annually by the state agency.	Low — State rates are set by rule; disputes require regulatory/administrative process, not standard appeals
Medicaid Managed Care (MCOs)	Each MCO negotiates its own rates with the provider. CO-45 must be verified against the specific MCO contract — not the state FFS rate. MCO rates are often at or slightly above state FFS but vary by plan.	Medium — Especially after plan transitions or MCO rebids, rates may not be correctly applied
UnitedHealthcare (Commercial)	Large national rate schedules; rates differ by product (HMO/PPO/EPO) and region. High volume of CO-45 adjustments. Underpayments are most common after contract renewals when updated rates are not applied correctly by the system.	Medium–High — Run quarterly audits; UHC underpayments are the most frequently reported by billing departments
Aetna / Cigna / Humana (Commercial)	Similar to UHC — national fee schedules with regional and product-level variation. Verify CO-45 allowed amounts against your specific contract addendum, not generic published rates.	Medium — Audit after any contract renewal or rate update notification
BCBS Plans	Independent local plans — rates and contracts vary significantly by state. National provider identifier (NPI) must be linked to the correct participating plan. Bluecard (out-of-state BCBS) uses the patient's home plan fee schedule; CO-45 verification requires the home plan rate, which can be difficult to obtain.	Medium–High for Bluecard claims; standard risk for local BCBS commercial

Prevention

Prevention checklist: catching CO-45 underpayments before they accumulate

You cannot prevent CO-45 from appearing — it is a structural feature of every contracted claim. What you can prevent is allowing underpayments disguised as CO-45 to go unrecovered.

Load all contract fee schedule addenda into your billing system — every payer's contracted rate for every CPT code you bill. This is the foundation of automated underpayment detection.
Run a monthly CO-45 variance report — group by payer + CPT code. Flag any line where the ERA allowed amount differs from your loaded contract rate by more than $1.
Audit CO-45 immediately after any contract renewal — new rates often take weeks to load correctly in payer systems. The 30–60 days after a rate update is the highest-risk period for systematic underpayments.
Verify credentialing is aligned with the correct fee schedule — providers credentialed under the wrong product type (e.g., HMO vs. PPO) will receive the wrong CO-45 allowed amount. This is especially common in multi-provider groups where new providers are added after initial credentialing.
Track CO-45 appeal win rates by payer — if you submit 20 underpayment reconsiderations to a payer and win 18, that payer has a systematic issue. Escalate to provider relations and request a fee schedule audit.
Set a write-off threshold for investigation — any single CO-45 adjustment above $200 (or your chosen threshold) should auto-flag for manual review before posting. High-value CO-45s are the most likely to be underpayments.
Use a contract management tool for 5+ payer contracts — spreadsheet-based contract tracking breaks down above five payers. Purpose-built tools (Waystar, PMMC, Recondo) automate the ERA vs. contract rate comparison at scale.

Appeal Template

CO-45 underpayment reconsideration letter

Use this template when the CO-45 allowed amount is lower than your contract rate. Replace the [bracketed fields] with your specifics.

VIA: Payer Claims Reconsideration / Provider Relations

Date: [Date]

Payer: [Payer Name]

Provider NPI: [NPI]

Provider Name: [Practice / Provider Name]

Claim Number: [Claim #]

Patient Account: [Account #]

Date of Service: [DOS]

CPT Code(s): [CPT]

RE: Underpayment Reconsideration — CO-45 Contractual Rate Discrepancy

Dear Provider Relations / Claims Reconsideration Team:

We are writing to request reconsideration of payment for the above-referenced claim. The Explanation of Remittance (ERA) dated [ERA date] shows an allowed amount of [$ERA allowed] for CPT [CPT code], resulting in a CO-45 adjustment of [$CO-45 amount].

Our provider agreement with [Payer Name], executed on [contract date], specifies a contracted rate of [$contracted rate] for CPT [CPT code] under the [product/network type, e.g., PPO In-Network] fee schedule. The ERA allowed amount of [$ERA allowed] represents an underpayment of [$difference].

Please find attached:

1. Original ERA / EOB dated [ERA date]
2. Provider Agreement Fee Schedule Addendum — page [X], showing CPT [code] at [$contracted rate]
3. Original claim for reference

We request that the claim be reprocessed at the contracted rate of [$contracted rate] and that the balance of [$difference] be remitted within [payer's stated reconsideration window] days.

Please direct any questions to:
[Billing Contact Name]
[Phone]
[Email]

Sincerely,
[Signature / Practice Administrator Name]
[Practice Name]

This template is a starting point. Adjust to match your specific contract language and the payer's reconsideration submission requirements. Some payers require online portal submission rather than written letters.

Frequently Asked Questions: CO-45

CO-45 means your billed charge exceeds the fee schedule or maximum allowable amount set by the payer. In a contracted relationship, this is expected on virtually every claim — it is the difference between what you billed and what you negotiated. You write off the CO-45 amount; you cannot bill the patient for it. CO-45 only signals a genuine problem when the allowed amount paid is lower than your contract says it should be, which is how underpayments remain invisible on ERAs for months.

No. CO-45 uses the CO (Contractual Obligation) group code, meaning you have agreed under your provider contract to absorb this amount as a write-off. Billing the patient for a CO-45 adjustment is a contract violation. In many states it also violates balance billing statutes (particularly for emergency services under the federal No Surprises Act). The full CO-45 amount must be adjusted off the patient's account.

CO-45 indicates a potential underpayment when the allowed amount on the ERA is lower than the fee schedule rate in your signed contract addendum for that specific CPT code. Example: your contract says CPT 99213 allows $95, but the ERA shows $78 allowed with CO-45 for $17. The $17 difference is recoverable. Underpayments are most common: (1) after contract renewals when updated rates are not loaded correctly, (2) when providers are credentialed under the wrong product/network type, and (3) for Medicare Advantage plans where each plan's rates differ from the standard Medicare fee schedule.

CO-45 underpayments are appealed as reconsideration requests, not standard medical necessity appeals. You need: (1) the original ERA/EOB showing the allowed amount paid, (2) the relevant page of your contract fee schedule addendum showing the correct contracted rate for that CPT code, (3) the claim number, date of service, NPI, and patient account number, and (4) a cover letter citing the discrepancy and requesting reprocessing at the contract rate. Submit to the payer's provider relations or claims reconsideration team within their appeal window — typically 90 to 180 days from the original payment date.

Yes. On Medicare FFS (Original Medicare) claims, CO-45 represents the standard contractual adjustment between your billed charge and the Medicare Physician Fee Schedule (MPFS) allowed amount. Medicare CO-45 is not a recoverable underpayment — MPFS rates are set by CMS annually and are not negotiable by individual providers. Medicare Advantage is different: each MA plan negotiates its own rates, so CO-45 on a Medicare Advantage claim should be compared against that specific plan's contract addendum, not the MPFS.

CO-45 and CO-97 are completely different denial types that are often confused. CO-45 means your billed charge exceeds the payer's allowed fee schedule — it is a rate/fee issue. CO-97 means the benefit for the service is already included in the payment for another service — it is a bundling issue triggered by NCCI (National Correct Coding Initiative) edits. CO-45 appears on nearly every contracted claim as a routine adjustment. CO-97 only appears when two services that are considered inclusive of each other are billed separately. They require entirely different remediation: CO-45 requires fee schedule comparison; CO-97 requires modifier review (59, XE, XS, XP, XU) or a clinical justification for separate billing.

Related Codes

Charge Exceeds Fee Schedule / Maximum Allowable

What to do when you see CO-45

How CO-45 behaves by payer type

Prevention checklist: catching CO-45 underpayments before they accumulate

CO-45 underpayment reconsideration letter

Frequently Asked Questions: CO-45

Denial codes commonly seen alongside CO-45

Not sure if your CO-45 write-offs are hiding underpayments?