A family medicine practice we worked with kept a whiteboard in the back office with one number on it: the dollar value of claims older than 90 days. The owner thought the problem was the biller. It wasn't. When we traced forty of those old claims back to the day of service, thirty-one had failed before the biller ever touched them: a wrong member ID typed at the front desk, a visit never marked complete, a referral that expired a week before the appointment.
That is the most useful thing to understand about medical billing. It is not a department. It is a chain of hand-offs that starts when the phone rings and ends when the account shows a zero balance, and every link is owned by a different person. When we audit a practice, we walk that chain in order, and this article does the same.
The medical billing process is the sequence of steps that turns a patient visit into a paid claim: registration, eligibility verification, authorization, the visit, coding and charge capture, claim scrubbing, electronic submission, payer adjudication, remittance posting, denial follow-up, patient statements and final account resolution. A clean claim moves through those steps once and is paid in two to four weeks. A dirty claim loops back, costs staff time at every loop, and often dies against a timely filing limit. The whole job of a billing operation is to make the first path the normal one.
Step 1: Scheduling and registration
Billing begins at the first contact, because the data captured there is copied onto every claim that follows. The scheduler collects the patient's legal name exactly as it appears on the insurance card, date of birth, sex, address, phone, the insurance plan name, the member ID, the group number, and the subscriber's details if the patient is a dependent. New-patient calls should also capture the reason for the visit, because that drives whether a referral or authorization is needed before the patient arrives.
The mistakes here are boring and expensive. A hyphenated surname entered without the hyphen. A nickname instead of the legal first name. A member ID with the letter O typed as a zero. Each one produces a rejection or a denial with reason code CO-16 (claim lacks information) and a remark like N382 (missing or invalid patient identifier), and each one costs two to three weeks. We tell front desks to read the ID back to the caller and to ask for a photo of the card through the portal before the visit.
Step 2: Eligibility and benefits verification
Eligibility verification confirms, before the visit, that the patient's coverage is active on the date of service and that the plan on file is the one that will pay. The electronic version is the HIPAA 270 inquiry and 271 response, which most practice management systems run automatically a day or two before the appointment. The 271 tells you whether coverage is active, the copay, deductible and coinsurance for the service type, whether the plan is an HMO that needs a primary care referral, and sometimes whether another payer is primary.
What the 271 does not tell you reliably is whether a specific service is covered or needs authorization, so for anything beyond a routine office visit the staff still call or use the payer portal. We ask practices to run eligibility twice: in a batch 48 hours ahead so there is time to call the patient, and again at check-in. The report to watch is the eligibility exception list, the patients whose 271 came back inactive, not found, or with a different payer. Those names need a phone call before the visit, not a surprise at the window.
Step 3: Referrals and prior authorization
Some services are paid only if the payer approved them in advance. Prior authorization applies to most advanced imaging, many injectable drugs, surgeries, durable medical equipment and a growing list of specialty medications. HMO plans also require a referral from the primary care physician on file for specialist visits. The request goes by payer portal, fax, phone or the HIPAA 278 transaction, and the response is an authorization number with a date range, a number of approved units or visits, and often a specific CPT code list.
The failure we see most is a valid authorization that does not match the claim: approved for CPT 73721 (MRI of a lower extremity joint) but the radiologist billed 73723 (with and without contrast), or approved for six physical therapy visits and the eighth one is billed. The payer denies with CO-197 (precertification absent). The fix is operational: the authorization number, approved codes, unit count and expiration date go into the practice management system on the appointment itself.
Step 4: Check-in and time-of-service collection
Check-in is the last moment before the visit where errors are cheap to fix. The front desk confirms the demographics, scans the current insurance card front and back, scans the photo ID, has the patient sign the financial policy and the assignment of benefits, and collects what is owed: the copay from the 271, any prior balance, and for high-deductible plans an estimate of the visit cost if the practice collects deposits.
Money not collected at check-in becomes a patient statement, and patient statements are the slowest, most expensive dollars in the practice. A $30 copay collected at the desk costs nothing. The same $30 billed after the visit costs a statement cycle, a reminder and staff time, and a meaningful share is never paid. The number to track is the time-of-service collection rate: copays collected divided by copays due. Practices that watch it weekly usually get it above 90 percent. Practices that don't are often under 60 and don't know it.
Step 5: The visit and the documentation
The clinical visit creates the record that supports every code on the claim. The provider documents the history, the exam, the assessment and plan, the time spent if time is used to select the level of service, any procedures performed, supplies used, drugs administered with the dose, and orders placed. The note must be signed, and signed by the person who rendered the service, because an unsigned or late-signed note is a documentation failure that payers treat as if the service never happened.
The billing team rarely sees this step, but it decides the outcome of every later one. A 99214 visit needs documentation of moderate medical decision making or 30 to 39 minutes of total time on the date of the encounter. An injection needs the drug name, dose and route. When we review medical necessity denials, the code was usually defensible; the note just didn't say what the provider actually did.
Step 6: Charge capture and coding
Charge capture turns what happened in the room into billable line items; coding translates them into CPT, HCPCS Level II and ICD-10-CM codes. In most small practices the provider selects the codes in the EHR and a coder or biller reviews them. The output is a set of claim lines, each with a procedure code, any modifiers, the diagnosis pointers that justify it, units, and the charge from the practice's fee schedule.
Two failure patterns dominate. The first is the missed charge: the encounter was never closed, the in-office procedure was never added, or the drug was given and the J-code was never billed. The report that catches this is the missing charge report (also called unbilled encounters): every checked-in appointment with no charges after 48 hours. The second is the code that won't pay: a diagnosis that does not support the procedure (CO-11), a modifier the payer rejects (CO-4), or two codes the National Correct Coding Initiative bundles together (CO-97 or CO-236). A scrubber catches many of these; a coder's review catches more.
Step 7: Claim creation and scrubbing
The practice management system assembles the claim from the registration data, the insurance data, the provider's enrollment data and the charge lines. For professional services that is the 837P electronic claim, the electronic form of the paper CMS-1500. Before it leaves, the claim passes through a scrubber, a rules engine that checks for the errors payers reject most often: an invalid NPI, a diagnosis code that needs a seventh character, a code pair that needs a modifier, a place of service that does not match the billing location, a rendering provider not enrolled with that payer.
Scrubber edits come from three places: the clearinghouse's general rules, payer-specific rules, and the practice's own custom edits built from its denial history. The third set is where the value is. The number to watch is the first-pass acceptance rate at the clearinghouse. We expect it above 95 percent. Below 90 means the front end of the chain is broken.
Step 8: Claim submission and acknowledgments
Claims go to payers either directly or, far more often, through a clearinghouse that reformats, batches and routes them. Two acknowledgments come back. The 999 says the file was valid and received. The 277CA (claim acknowledgment) says, claim by claim, whether the payer accepted the claim into adjudication or rejected it before processing, with a claim status category code (A1 acknowledged, A2 accepted, A3 or A7 rejected) and a status code that says why. A rejected claim never reaches adjudication, so it never shows up on a remittance and never generates a denial letter. It just sits in the clearinghouse rejection report.
That report is the single most neglected report in small practices. We have seen rejection queues with hundreds of claims that nobody opened for months, each one silently aging toward a timely filing limit. The routine is simple: someone opens the clearinghouse the morning after each submission, works every rejection, and resubmits the same day. Paper claims still exist for some workers' compensation and auto carriers; they get no acknowledgment at all, so the follow-up date goes in a tickler the day they are mailed.
Step 9: Payer adjudication
Adjudication is the payer's internal processing: confirming eligibility on the date of service, checking the provider's contract status, applying medical policies and bundling edits, pricing the lines against the fee schedule, and applying the member's deductible, copay and coinsurance. The output is a decision per line: paid, reduced, denied, or pended for more information.
Payers have timelines for this. Medicare's payment floor means electronic clean claims are not paid before the fourteenth day after receipt, and Medicare owes interest on clean claims not paid within 30 days. Most states have prompt-pay laws that give commercial payers 30 to 45 days for clean claims. The practical point is that a claim with no response after 30 days is not "in process", it is lost, and someone needs to check its status by portal or by the 276/277 claim status transaction.
Step 10: Remittance and payment posting
When the payer pays, it sends two things: the money, by electronic funds transfer or check, and the explanation, as an electronic remittance advice (the 835 transaction) or a paper explanation of benefits. The 835 lists each claim and line, the billed, allowed and paid amounts, the amount moved to patient responsibility, and the adjustment reason codes that explain every dollar of difference. The group code tells you who absorbs each adjustment: CO (contractual obligation, written off), PR (patient responsibility), OA (other adjustment) and PI (payer initiated).
Posting is matching those remittance lines to the open charges in the practice management system. Most systems auto-post 835 files; the staff's job is the exceptions: payments that do not match a claim, takebacks and interest. Two controls matter. Every 835 must reconcile to a bank deposit, to the penny. And every zero-pay line must create a follow-up task, because a denial that is posted and forgotten is a write-off with extra steps.
Step 11: Denials, corrections and appeals
A denial is a processed claim the payer refused to pay in full. Denial management means sorting denials by cause, fixing what can be fixed, appealing what deserves appeal, and feeding the cause back to the step that created it. The adjustment reason code tells you which step that was. CO-16, CO-29 and CO-18 (information, timely filing, duplicate) are billing-office failures. CO-27 and CO-22 (coverage terminated, another payer primary) are eligibility failures. CO-197 is an authorization failure. CO-50 and CO-11 (medical necessity, diagnosis mismatch) point to coding or documentation. You can look any code up in our denial codes tool.
Corrections and appeals follow different routes. A claim with a wrong code or a missing modifier goes back as a corrected claim, frequency code 7 in the 837 (item 22 on the CMS-1500 with the original claim number). A claim denied on a judgment, such as medical necessity, needs a written appeal with the note, the policy language and a cover letter, inside the payer's appeal window. Those windows run from 60 to 180 days from the denial depending on the payer; Medicare's first level (redetermination) allows 120 days. The full workflow is on our denial management page.
Step 12: Patient statements and patient balances
After adjudication, the remaining balance moves to the patient: the deductible and coinsurance from the remittance, the copay if it wasn't collected, and any non-covered services the patient agreed to pay for. The statement should show the date of service, the service in plain words, the charge, what insurance paid and adjusted, and what the patient owes, with an online payment link.
The statement cycle is usually three statements about 30 days apart, then a final notice and, if the practice uses one, referral to a collection agency. Two things decide whether balances get paid. First, speed: a statement sent within a week of the remittance is paid far more often than one sent six weeks later, when the patient has forgotten the visit. Second, the estimate given at check-in; patients who were told what to expect pay, patients surprised by a bill call to argue.
Step 13: Accounts receivable follow-up and the zero balance
Accounts receivable follow-up is the discipline of touching every open claim before it ages into trouble. The working tool is the aging report, split by payer and by age bucket (0 to 30, 31 to 60, 61 to 90, 91 to 120, over 120 days), worked oldest and largest first. Each touch ends in a documented outcome: paid on a given date, denied for a given reason, needs a corrected claim, needs an appeal, or payer says not on file, which means it was never received and must be resubmitted at once.
A claim reaches zero balance in one of four ways: paid in full by payer and patient, paid with a contractual adjustment that matches the contract, written off for a documented reason with the manager's approval, or refunded if an overpayment created a credit balance. The reasons matter because write-offs are where leakage hides. A timely filing write-off is not bad debt; it is an operational failure, and we track it separately so it stands out. The numbers we watch are days in accounts receivable, the percentage of AR over 90 days, and the net collection rate (payments divided by charges less contractual adjustments). Healthy independent practices generally run under 40 days in AR, under 15 percent over 90 days, and a net collection rate in the high 90s, though targets depend on specialty and payer mix.
Step 14: Reporting and the feedback loop
The last step is the one that makes the first thirteen get better. Once a month, someone looks at the denial report by reason code, the missing charge report, the clearinghouse rejection trend, the time-of-service collection rate, the aging by payer and the write-off log, and asks one question: which step broke most often, and what change upstream would stop it? A rise in CO-27 means eligibility is being skipped. A rise in invalid member ID rejections means registration needs a card photo. A rise in CO-197 means the authorization fields are not being filled in.
This loop is what separates a billing operation from a billing department. A department works denials. An operation changes the front desk script so the denial does not happen again. That is also what an RCM audit does: it walks a sample of accounts through all fourteen steps and reports where the money left.
The billing process at a glance
| Stage | Who owns it | When | Output | Common failure |
|---|---|---|---|---|
| Scheduling and registration | Scheduler, front desk | First contact | Complete demographic and insurance record | Wrong member ID, nickname instead of legal name |
| Eligibility verification | Front desk or billing | 48 hours before and at check-in | 271 response, copay and deductible noted | Inactive coverage found after the visit (CO-27) |
| Referral and authorization | Referral coordinator, clinical staff | Before the service | Authorization number, codes, units, dates on the appointment | Auth does not match the billed code (CO-197) |
| Check-in and collection | Front desk | Day of service | Signed forms, card scans, copay collected | Copay deferred to a statement |
| Visit and documentation | Provider, clinical staff | Day of service | Signed note supporting each code | Unsigned note, missing drug dose or time |
| Charge capture and coding | Provider, coder | Within 24 to 48 hours | Claim lines with CPT, HCPCS, ICD-10-CM, modifiers | Unclosed encounter, missed J-code, bundling conflict |
| Claim creation and scrubbing | Billing | Daily | Clean 837P | Edits never updated from denial history |
| Submission and acknowledgment | Billing | Daily, worked next morning | 999 and 277CA accepted | Rejection report nobody opens |
| Adjudication | Payer | 14 to 45 days | Paid, denied or pended lines | No status check at day 30 |
| Remittance and posting | Billing, payment poster | On receipt | 835 posted and reconciled to deposit | Zero-pay lines posted without a task |
| Denials and appeals | Billing, provider for appeals | Within 7 days of the denial | Corrected claim or appeal filed | Appeal window missed |
| Patient statements | Billing | Within 7 days of remittance | Clear statement with payment link | Statement sent weeks late |
| AR follow-up and zero balance | Billing | Weekly by aging bucket | Documented outcome per claim | Timely filing write-off |
| Reporting and feedback | Practice manager | Monthly | Upstream process change | Reports produced, nothing changed |
Questions we hear
How long does the medical billing process take from visit to payment?
For a clean electronic claim to a commercial payer or Medicare, two to four weeks from the date of service is normal: a day or two to code and submit, a day for acknowledgments, 14 to 30 days for adjudication, and a few days for the funds and the 835 to arrive. The patient portion takes longer, usually 30 to 90 days through the statement cycle. Every loop back, whether a rejection, a denial or a corrected claim, adds two to six weeks, which is why the first-pass rate drives cash flow.
What is the difference between a rejected claim and a denied claim?
A rejected claim failed a format or data check at the clearinghouse or the payer's front door and was never adjudicated; it appears on the 277CA or the clearinghouse report, not on a remittance. A denied claim was adjudicated and refused, so it appears on the 835 with a reason code. Rejections are fixed and resubmitted as new claims. Denials are corrected (frequency code 7) or appealed in writing. Both count against timely filing, and a rejected claim that was never resubmitted is treated by the payer as never received.
Which reports should a practice owner look at every month?
Five are enough: the aging report by payer with the percentage over 90 days, the denial report by adjustment reason code, the missing charge report, the time-of-service collection rate, and the write-off log by reason. If the owner only has time for one, take the aging report and ask why anything is in the over-120 bucket.
Should a small practice bill in house or outsource?
It depends on volume, specialty and whether the practice can keep a trained biller busy and current. A solo primary care practice often cannot justify a full-time biller and loses money when that one person is on vacation. A multi-provider surgical group may do better in house. The honest test is the numbers above: if days in AR, first-pass rate and over-90 percentage are healthy and the owner can see them monthly, the current model works. If nobody can produce them, the model is broken regardless of who runs it. Our medical billing page explains what stays with the front desk either way.
Where does the most money get lost in the process?
In our audits, the biggest leaks are rarely dramatic: missed charges, copays never collected, rejections never worked, and denials posted without follow-up until timely filing passes. Each is small per occurrence and large per year. Under-coding, a 99213 billed for a visit that documents a 99214, is the other large one, and it never appears on a denial report because the payer is happy to pay less.
Sources and references
- Electronic Billing & EDI Transactions, CMS: how Medicare receives electronic claims, the HIPAA transaction standards (837, 835, 270/271, 276/277) and links to the MAC EDI resources.
- Medicare Claims Processing Manual (Publication 100-04), CMS: the chapter index; Chapter 1 covers general billing requirements and timely filing, Chapter 12 physician services, Chapter 29 appeals.
- CMS 1500, CMS: the official form page for the CMS-1500 paper claim, with the current version and instructions reference.
- Place of Service Codes, CMS: the two-digit place of service code set used in item 24B and the 837P, with definitions.
- X12 Transaction Sets, X12: the standards body's index of the EDI transactions used in billing, including the 837, 835, 277CA and 999.
- Administrative Simplification, CMS: the HIPAA rules that require standard transactions, code sets and identifiers, and what covered entities must use.
- What is Medical Billing?, AAPC: a plain-language overview of the billing role, the claim cycle and how it differs from coding.
