When your deposits look right but your A/R report does not, medical payment posting accuracy is often the cause.
Medical payment posting accuracy means every payer payment, adjustment and patient payment lands on the right claim line, with the right group and reason code, and ties back to a real deposit. When posting slips, A/R, net collections and patient balances drift away from reality, even though the cash arrived.
Most of that drift traces to a few habits: posting batches by total instead of by line, leaving patient prepayments unapplied, and writing off amounts that were never contractual. Daily reconciliation of each ERA to its deposit, plus line-level balancing, lets you catch these errors before month-end.
This guide shows how an ERA is supposed to balance, which errors distort your reports, and how to audit posting each month.
Key Takeaways
- Every ERA line must balance: the billed charge minus all adjustments equals the payer’s payment. A line that does not balance is a posting problem.
- In network, the contractual adjustment equals the billed charge minus the allowed amount. The payer payment, the patient share and any reductions, such as Medicare sequestration, add up to the allowed amount.
- Match each EFT to its ERA by the reassociation trace number, not by dollar amount.
- Provider-level adjustments, such as recoupments and interest, change the deposit without touching any single claim.
- Patient prepayments belong on the encounter they pay for, and real credit balances need a refund decision.
- Never write off a short payment as a contractual adjustment until you compare it with your fee schedule.
Why Your Deposits and Your Reports Disagree
Practice owners usually notice the problem from the top down. Deposits look normal, yet the aging report keeps showing paid claims. Meanwhile, net collections swing from month to month, and patients call about bills they already paid.
Three different things produce that picture. First, timing: an ERA and its EFT do not always arrive on the same day. Second, real payer behavior, such as a recoupment or an underpayment. Third, posting errors. The fix depends on which one you have, so separate them before anyone changes a ledger.
| What you see | Likely posting cause | What to check first |
|---|---|---|
| Paid claims still aging in A/R | Payment applied to the wrong patient, claim or date of service | The claim number and service date on the ERA against the ledger |
| Unexplained patient credit balances | Duplicate posting, or a prepayment applied twice | Whether the same ERA or receipt was posted more than once |
| A/R drops faster than cash comes in | Write-offs larger than the contract allows | Adjustment amounts against the allowed amount and fee schedule |
| Deposit smaller than the claim payments | Provider-level recoupment not posted | The provider-level adjustment section of the ERA |
| Patients billed for amounts the plan owes | Balance moved to the patient before a secondary payer was billed | Coordination of benefits and the secondary claim status |
What Medical Payment Posting Accuracy Means on Every ERA Line
An electronic remittance advice (ERA) is the X12 835 file a payer sends to explain a payment. It reports each claim and service line with its charge, payment and adjustments. Therefore, it already contains the arithmetic your posting must reproduce.
The balancing rule
X12, the body that maintains the 835 standard, describes the rule plainly. At the line and claim level, the submitted charge minus all monetary adjustments must equal the amount paid. The same interpretation notes that the allowed amount is informational and is not part of the financial balancing.
Billed charge − all adjustments (CO, PR, OA, PI) = payer payment. If a posted line does not satisfy this equation, something was skipped, mis-keyed or posted twice.
Group codes tell you who owns each dollar
Every adjustment carries a group code and a claim adjustment reason code (CARC). The group code assigns financial responsibility, so a wrong group code moves money to the wrong party.
| Group code | Meaning | Typical posting treatment |
|---|---|---|
| CO | Contractual obligation | Provider write-off; not billable to the patient |
| PR | Patient responsibility | Transfer to the patient, or to a secondary payer first |
| OA | Other adjustment | Review the reason code; for example, prior-payer amounts on secondary claims |
| PI | Payer-initiated reduction | The patient does not owe it, and no contract term supports it; review it and appeal if it looks wrong |
For Medicare, CMS states that providers may bill beneficiaries only when an adjustment carries group code PR, according to its payment and remittance advice guidance. The common reason codes come from the X12 CARC list: 1 is the deductible, 2 is coinsurance, 3 is the copay, 45 means the charge exceeds the fee schedule, and 253 is sequestration.
The payment posting formula, with a Medicare example
For an in-network claim, three relationships hold. First, the contractual adjustment equals the billed charge minus the allowed amount. Second, the payer payment plus patient responsibility equals the allowed amount. Third, other reductions come out of the payer’s share.
Medicare sequestration is a common example. Noridian, a Medicare contractor, explains that Medicare applies a 2% reduction to its payment after it determines the deductible and coinsurance, and reports it as CO 253. The reduction continues until further notice, and the patient’s share does not change.
| Hypothetical line | Amount | Code |
|---|---|---|
| Billed charge | $180.00 | — |
| Allowed amount | $100.00 | Informational |
| Contractual adjustment | $80.00 | CO-45 |
| Coinsurance (deductible already met) | $20.00 | PR-2 |
| Sequestration (2% of $80.00) | $1.60 | CO-253 |
| Medicare payment | $78.40 | — |
The line balances: $180.00 − $80.00 − $20.00 − $1.60 = $78.40. In addition, the payment, patient share and sequestration add back to the $100.00 allowed amount. For an out-of-network claim, however, part of the difference between charge and allowed amount may carry group code PR, so check the group code instead of assuming CO.
Check your own ERA line
Try it: ERA line balance check
The fields hold the Medicare example above. Enter the amounts from your own ERA line and your fee schedule to see whether the line balances, whether the payer underpaid, and what the patient owes.
Line balance: Balanced. The charge minus all adjustments equals the payment.
Fee schedule check: The allowed amount matches your expected rate.
Contractual adjustment check: CO-45 matches the charge minus the allowed amount ($80.00).
Allowed amount check: Payment, patient share and reductions add up to the allowed amount.
Sequestration check: CO-253 equals 2% of Medicare’s share after the patient share ($80.00).
Patient account: No balance due. The amount collected at the visit covers the patient share.
Educational check only. Your payer’s ERA, contract and fee schedule decide the correct amounts.
Five Posting Errors That Distort Your Financials
Most posting errors fall into five patterns. Each one leaves a recognizable mark on your reports, so you can trace it back.
1. Batch posting by total instead of by line
A batch can balance to the deposit while individual payments sit on the wrong accounts. For example, a $500 batch still totals $500 if a $200 payment lands on the wrong claim. As a result, one account looks overdue, and another shows an unexplained credit. Staff then chase a balance that was already paid.
2. Unallocated patient prepayments
Front-desk payments often post as unapplied cash, or to the account instead of the visit. After the ERA posts the patient share, the same visit shows a balance due, while the prepayment sits elsewhere as a credit. Consequently, the patient receives a statement for money they already paid.
3. Wrong contractual write-offs
This error can cost the most, because it erases revenue quietly. A short payment written off as CO-45 makes A/R look clean while the practice absorbs an underpayment. Similarly, a denial posted as a contractual adjustment lets the appeal window expire. Treat the opposite error with the same care. If a patient-responsibility amount posts as CO, you never collect money the patient owes.
4. Missed provider-level adjustments
Some ERA adjustments belong to the provider, not to any claim. CMS lists examples such as interest on late clean claims and deductions for prior overpayments. A Medicare withhold, for instance, reduces the payment on the remittance to repay a debt the practice owes. If you post only the claim payments, the deposit will not match, and the recouped claim stays wrong. See our guide to recoupment in medical billing for the recovery side.
5. Duplicates and reversals
Payers sometimes resend an ERA, and clearinghouses can deliver a file twice. Therefore, check the trace number before you post. Claim reversals and corrections also need both entries posted, so the net result is right.
Identifying Contractual Adjustment Errors
A contractual adjustment is normal. The error is a write-off that does not match your contract. To learn how these adjustments arise, see our explainer on the contractual adjustment in medical billing. Then use these four checks to separate valid write-offs from errors.
- Compare the allowed amount with your fee schedule. Load expected rates by payer and code, then flag lines where the allowed amount falls below them.
- Confirm the group code. CO-45 belongs to an in-network fee schedule reduction. PR-45 means the patient is liable, which can apply when you are out of network.
- Separate denials from adjustments. A zero payment with a denial reason code needs follow-up, not a write-off.
- Map special codes correctly. Sequestration (CO-253) is a provider write-off. Our post on sequestration in medical billing covers how to map it.
Many practices do not run this comparison often. In a February 2025 MGMA Stat poll with 193 responses, 30% of practice leaders said they audit payer payments against contracted rates monthly. Another 18% audit quarterly, and 30% audit annually.
Do not write off a short payment as a contractual adjustment until you compare it with the contracted rate. Once it is written off, nobody looks at it again.
Insurance ERA Reconciliation for Practices: A Daily Routine
Insurance ERA reconciliation for practices means proving three things every day. Each ERA matches a deposit, each claim payment is posted, and every difference has a documented reason.
How the ERA and the EFT connect
The ERA and the electronic funds transfer (EFT) travel separately. Under the federally adopted CAQH CORE reassociation rule, the health plan places a reassociation trace number in the ERA and the same number in the EFT addenda. CMS explains this in its EFT and ERA reassociation basics.
The same rule sets timing. The plan must release the ERA no sooner than three business days before the EFT effective date. It also must release it no later than three business days after that date. An EFT or ERA counts as late or missing four business days after the other one arrives. At that point, follow the payer’s written resolution procedures.
Ask your bank to deliver the full CCD+ addenda with each deposit. Without it, you cannot see the trace number, and you will end up matching deposits by amount.
The daily steps
- Log every ERA and every deposit. Record payer, payment date, trace number and amount.
- Match by trace number. Then confirm that the ERA’s total payment equals the EFT or check amount.
- Explain the total. The ERA total equals the claim payments plus or minus provider-level adjustments. Post those adjustments as their own transactions.
- Post line by line. Apply payments, CO and PR adjustments, and reason codes to each service line. Do not post a lump sum.
- Reconcile manual payments. Tie paper checks to their EOBs, and tie front-desk receipts to the day’s deposit and card-processor report.
- Work the exceptions. Keep a log for unmatched deposits, missing ERAs and unapplied cash. Close each item with a note.
Do not force a batch to balance with an unexplained adjustment. Every difference needs a cause, such as timing, a recoupment or a posting error.
Patient Copay Allocation Best Practices
Patient payments cause a large share of false balances, because they arrive before the claim is adjudicated. The goal is simple. Each dollar should sit on the visit it pays for, and the patient balance should match the PR amounts on the ERA.
When to collect copays, deductibles and coinsurance
Copays are fixed amounts that patients usually pay when they receive the service. Still, confirm the timing in each payer contract and provider manual. Deductibles and coinsurance are estimates until the payer adjudicates the claim.
Medicare adds a reporting step. First Coast, a Medicare contractor, says amounts collected before a Part B claim is filed must appear in item 29 of the claim form on assigned claims. It advises against collecting the deductible before Part B pays. However, it allows coinsurance collection when the amount can be predicted accurately. Check your own contractor’s guidance before you set front-desk rules.
How to post prepayments so they do not become disputes
- Link each prepayment to the specific encounter, not just to the patient account.
- Hold estimated deductible or coinsurance payments as unapplied until the ERA posts.
- Apply the prepayment to the PR amounts on that ERA line, then review what remains.
- Bill any secondary payer before you move a balance to the patient.
- Send a statement only after the ledger matches the ERA.
Our guide to patient balance billing rules covers what you may bill once the claim is final.
What a 20% coinsurance after the deductible means
If the deductible is met and the allowed amount is $100, a 20% coinsurance makes the patient share $20. The plan’s share is the remaining $80, less any reductions such as sequestration. If the front desk collected $50 as an estimate, the visit now carries a $30 credit.
Credit balances and refunds
A real credit balance means someone overpaid. For Medicare overpayments, 42 CFR 401.305 requires you to report and return the overpayment within 60 days after you identify it. The rule suspends that deadline while you run a timely, good-faith investigation of related overpayments, but for no more than 180 days after you identify the first one. Separately, refund a Medicare patient who paid more than the deductible and coinsurance owed. Other patient and commercial refunds follow your payer contracts and state law. Therefore, review credit balances at least monthly, and document each refund decision.
Payment Posting Audit for Physicians: A Monthly Checklist
Daily reconciliation keeps cash and ERAs aligned. A monthly payment posting audit for physicians tests whether the posting itself was right. Pull a sample of posted ERA lines and patient receipts, then check each one against its source record.
- Each payment sits on the correct patient, claim and date of service.
- Every sampled line balances to the ERA, including group and reason codes.
- Contractual adjustments match the fee schedule, and short payments went to follow-up.
- Provider-level adjustments were posted and tied to the original claims.
- Prepayments were applied to the right encounter, and unapplied cash was researched.
- Credit balances have a refund or transfer decision on file.
- Corrections show the date, the reason and the person who made them.
What to track over time
Track the share of sampled lines that needed correction, unapplied cash and its age, and unexplained deposit differences. Also run a monthly A/R roll-forward: beginning A/R plus charges, minus payments (net of refunds) and adjustments, should equal ending A/R. No national standard sets a target posting accuracy rate, so set a baseline from your own audits and watch the trend.
Finally, separate duties where staffing allows. The person who posts payments should not also approve large write-offs or the bank reconciliation.
Protect the Numbers You Make Decisions On
Medical payment posting accuracy is not a back-office detail. Your A/R, net collections and patient statements all rest on it. When each ERA line balances, each deposit matches its trace number, and each prepayment sits on its visit, your reports reflect what really happened.
Start with the daily routine, then add the monthly audit. If your team cannot keep up, our payment posting services can take on the daily posting and reconciliation work.
Seeing gaps between expected reimbursement and your deposits? Request a review from Steady Medical Billing’s payment posting services.
Frequently Asked Questions
What is the formula for payment posting in medical billing?
On every ERA line, the billed charge minus all adjustments equals the payer payment. In network, the contractual adjustment is the billed charge minus the allowed amount. The payer payment, the patient share and any reductions, such as sequestration, add up to the allowed amount.
What are the steps in payment posting?
Match the ERA, EOB or patient receipt to its deposit. Next, post payments and adjustments to each service line with the right group and reason codes. Then move patient responsibility to a secondary payer or the patient, and work the exceptions.
When should a copayment be collected from a patient?
Patients usually pay the copay at the time of service, but the plan and your payer contract decide. Deductibles and coinsurance stay estimates until the payer adjudicates the claim. For Medicare, follow your contractor’s guidance on collecting before payment.
What does CO-253 mean on an ERA?
CO-253 is the Medicare sequestration reduction. Medicare takes 2% off its own payment after it applies the deductible and coinsurance. Post it as a provider write-off; you cannot bill it to the patient.
Why don’t the claim payments on an ERA add up to the deposit?
The ERA often carries provider-level adjustments, such as a recoupment or interest, that change the payment total. A deposit can also arrive on a different day from its ERA. Match them by trace number, and after four business days follow the payer’s resolution procedures.
How often should a practice audit payment posting?
Reconcile ERAs, deposits and patient receipts every business day. Then audit a sample of posted lines, credit balances and unapplied cash each month. Increase the sample when error patterns appear.
