Practice economics tool

COB Underpayment Checker

Find possible secondary-payment shortfalls that were offset by larger contractual adjustments.

Arithmetic first. Accusations never.

The worksheet flags a pattern. The plan document, EOBs, contract, and applicable law decide what is owed.

Runs entirely in your browser Do not enter patient information Reviewed July 2026

Step 1

Rebuild the claim line by line.

Enter the office's documented expected secondary payment. The tool does not invent that number.

Payer label (optional) Claim reference (optional, no patient name)

Step 2

Check the pattern.

Enter a service line

Possible underpayment $0.00

Expected secondary payment minus actual secondary payment.

Excess posted adjustment $0.00

Posted adjustment above the amount implied by your expected payment.

Unexplained claim balance $0.00

Amount not reconciled by payments, adjustments, or patient responsibility.

Add the claim lines from both EOBs to see whether a payment gap was mirrored by an adjustment.

Step 3

Ask for the adjudication math.

Copy a neutral worksheet summary for the payer, clearinghouse, contract specialist, or state regulator.

Before calling it an underpayment

Verify four things.

01The COB method named in the plan document or EOB
02Allowed amount and primary payment for each CDT line
03Actual secondary payment and every posted adjustment
04The contractual basis for any write-off that replaced payment

Sources and limits

COB is contract-specific.

Traditional COB, maintenance of benefits, carve-out, and nonduplication can produce different secondary payments. Self-funded plans and state-regulated plans may also follow different rules.

ADA guidance on coordination of benefits Explains common COB methods and warns against posting write-offs before all plans have paid. NAIC Coordination of Benefits Model Regulation Model framework for benefit order and secondary-plan calculations; state adoption and plan applicability vary. CMS coordination-of-benefits overview Official overview of COB transactions and relative payer responsibility. Medicare-specific rules may differ.

Educational reconciliation tool only. It does not determine coverage, contract rights, patient responsibility, legal liability, or whether a payer acted improperly. Confirm the plan's COB method and appeal deadlines.