Medical Billing & Coding (CBCS) — Complete Study Guide (2026)

Reimbursement is how providers get paid and how patient responsibility is calculated. This is the most math-heavy domain — and, for that reason, one of the easiest to score on, because the questions are arithmetic that always follows the same order of operations. The single most important habit: patient responsibility is calculated from the allowed amount, never from the billed charge. Master that and most reimbursement questions fall.

(Every dollar, percentage, RVU, and conversion factor below is a teaching number, not a current published rate. Always recompute using the real figures on your date of service.)

4.1 The allowed amount and patient responsibility

The allowed amount (also allowable or maximum allowable) is the most a payer recognizes as payable for a covered service under its fee schedule or contract. It is frequently less than the provider's billed charge. Every downstream number — deductible, coinsurance, plan payment — is based on the allowed amount.

For a participating (in-network) provider, the difference between the billed charge and the allowed amount is a contractual adjustment (write-off) that cannot be balance-billed to the patient.

The out-of-pocket maximum caps a patient's cost-sharing in a benefit period. Once the patient's combined deductible + coinsurance + copays reaches that cap, the plan pays 100% of covered, in-network services for the rest of the period. (Premiums and non-covered services do not count toward the cap.)

Worked example — the full breakdown

A participating provider bills $300 for a service with a contracted allowed amount of $200. The patient's deductible is already met, and the plan pays 80% (patient coinsurance 20%).

• Plan pays: 80% of $200 = $160.
• Patient coinsurance: 20% of $200 = $40.
• Contractual write-off: $300 − $200 = $100 (not billable to the patient).
• Check: $160 (plan) + $40 (patient) = $200 (allowed). The $100 write-off sits outside the allowed amount.

The patient owes $40 — computed from the $200 allowed, not the $300 charge.

Key concept. Patient responsibility comes from the allowed amount, not the billed charge. For a participating provider, the charge − allowed gap is a write-off and cannot be balance-billed.

4.2 Cost-sharing definitions

Three forms of cost-sharing — memorize the distinctions:

• Copayment (copay) — a fixed dollar amount per covered service (e.g., $30 office visit, $15 generic drug). Flat, known in advance, usually collected at the time of service.
• Deductible — the fixed amount the patient must pay each benefit period before the plan begins to pay its share (e.g., a $1,500 annual deductible). Many preventive services are exempt and covered before the deductible is met.
• Coinsurance — the patient's share as a percentage of the allowed amount, owed after the deductible is satisfied (e.g., 80/20, plan 80% / patient 20%). Because it is a percentage, the dollar amount rises with the cost of the service.

Order of operations when a claim has several: apply the deductible first, then coinsurance to the remaining allowed amount; handle any fixed copay per plan design. All of these accumulate toward the out-of-pocket maximum.

Worked example — deductible then coinsurance

Allowed amount $1,000, remaining deductible $200, coinsurance 20%.

1. Apply the deductible first: patient pays $200; remaining allowed = $1,000 − $200 = $800.
2. Coinsurance: 20% of $800 = $160.
3. Patient total: $200 + $160 = $360.
4. Plan pays: $800 − $160 = $640.
5. Check: $360 + $640 = $1,000 (the full allowed amount).

Key concept. Copay = fixed dollars per service; deductible = pay-first threshold each period; coinsurance = a percentage after the deductible. Deductible first, then coinsurance on what remains.

4.3 Physician and facility payment systems

Different settings use different methodologies — match the system to the setting.

RBRVS (physician services)

Medicare prices physician services with the Resource-Based Relative Value Scale (RBRVS). Each service gets three relative value units (RVUs):

• Work RVU (physician time, skill, effort),
• Practice expense RVU (overhead),
• Malpractice RVU (liability).

Each RVU is adjusted for local costs by a Geographic Practice Cost Index (GPCI), summed, and multiplied by a national dollar conversion factor (CF).

Formula: Payment = [(Work RVU × GPCI) + (PE RVU × GPCI) + (MP RVU × GPCI)] × CF.

Worked example (teaching numbers): a service totals 2.0 fully geographically-adjusted RVUs, and the conversion factor is $33.00. Payment = 2.0 × $33.00 = $66.00. If the CF instead were $36.00, the same service would pay 2.0 × $36.00 = $72.00 — which is exactly why a conversion-factor change moves every physician fee.

Facility prospective payment

• Inpatient hospital: DRGs (Diagnosis-Related Groups). Each admission is grouped by diagnoses, procedures, and other factors into a DRG with a fixed payment weight, so the hospital receives a predetermined amount per admission regardless of exact resources used — an incentive for efficiency.
• Hospital outpatient: APCs (Ambulatory Payment Classifications) — the outpatient counterpart, paying a set amount per group of similar services.

Fee-for-service vs. capitation

• Fee-for-service (FFS) pays separately for each service, so revenue rises with volume.
• Capitation pays a fixed amount per member per month (PMPM) to care for each enrolled patient regardless of how many services that patient uses — shifting utilization risk to the provider.

Worked example — capitation: a group is paid $25 PMPM for 2,000 enrolled members. Monthly capitation revenue = $25 × 2,000 = $50,000, whether the members use 0 visits or 1,000 visits that month. Under FFS, the same 1,000 visits at, say, $60 allowed each would pay $60 × 1,000 = $60,000 — more revenue, but only if the volume occurs. The two models reward opposite behaviors.

Key concept. RBRVS prices physician claims (RVUs × GPCI × CF). DRGs price inpatient stays; APCs price outpatient facility services. FFS rewards volume; capitation pays PMPM and shifts risk to the provider.

4.4 Reimbursement math drills

The order never changes: start with the allowed amount → subtract any unmet deductible → apply coinsurance to what remains → treat charge − allowed as a write-off for participating providers.

Drill 1 — deductible already met. Allowed $1,000, deductible met, coinsurance 20%.

• Patient: 20% of $1,000 = $200. Plan: $800. Nothing else due.

Drill 2 — deductible still owed. Allowed $1,000, remaining deductible $300, coinsurance 20%.

• Deductible first: patient $300; remaining $700.
• Coinsurance: 20% of $700 = $140.
• Patient total: $300 + $140 = $440. Plan: $560. Check: $440 + $560 = $1,000. ✓

Drill 3 — the write-off. Same service, provider billed $1,400, allowed $1,000.

• Because the provider participates, the $1,400 − $1,000 = $400 gap is a contractual write-off — not billable to the patient. The patient still owes only the cost-sharing computed from the $1,000 allowed.

Drill 4 — copay plus coinsurance. Allowed $500, a $30 copay applies, deductible met, coinsurance 20%.

• Copay: $30. Coinsurance: 20% of $500 = $100. (Plan designs vary on whether coinsurance is figured before or after the copay; here we treat the copay as a separate fixed fee.)
• Patient: $30 + $100 = $130. Plan: $500 − $100 = $400 (the copay is the patient's separate fixed share).

Balance billing — charging the patient the difference between the billed charge and the allowed amount — is generally prohibited for participating providers and, for many services, further restricted by federal surprise-billing protections.

Key concept. Write the numbers in order every time: allowed − deductible, × coinsurance; keep the charge-to-allowed gap out of the patient's column for participating providers.

4.5 The revenue cycle

Everything in this book lives inside the revenue cycle — the full financial life of a patient encounter, from scheduling to a zero balance. Know the stages and where errors originate:

1. Pre-registration / scheduling — capture demographics and insurance before the visit.
2. Registration & eligibility verification — confirm coverage, benefits, copay, deductible status, and prior authorization requirements. Front-end errors here cause most back-end denials.
3. Charge capture & coding — the encounter is documented, coded (ICD-10-CM, CPT/HCPCS), and charges are entered.
4. Claim scrubbing & submission — edits are run; clean claims go out via clearinghouse (837).
5. Payer adjudication — the payer processes and returns a remittance (835).
6. Payment posting — record payments, apply contractual adjustments, move the correct remaining balance to the patient or secondary payer.
7. Denial management & appeals — read CARC/RARC, fix root causes, appeal when warranted.
8. Patient collections — send statements after insurance processes, offer payment plans, escalate per policy and law.
9. A/R management & reporting — track days in A/R and % of A/R over 90 days; work the aging report oldest and largest first.

Payment posting and A/R detail

• Payment posting records each payment against the correct claim/line, applies the write-off to the allowed amount, and moves the correct balance onward. Electronic remittance (835) can auto-post, but exceptions and denials need human review. A missed contractual adjustment makes the account balance wrong and sends staff chasing phantom dollars.
• A/R aging sorts unpaid balances into buckets — current, 31–60, 61–90, over 90 days. The older a balance, the less likely it collects, so work the oldest and largest first.
• Patient statements should itemize services and dates, charges, insurance payments and adjustments, and the balance due, and should go out only after insurance has processed, so the patient sees a correct net balance rather than the full charge.

Worked example — payment posting

A remittance for a $500 billed service shows allowed $400, plan paid $320, patient coinsurance $80 (20% of $400), and a $100 contractual adjustment. Correct posting: record $320 payment, post the $100 as a contractual write-off, and move $80 to patient responsibility. If the biller forgot the $100 write-off, the system would still show a $180 balance ($500 − $320) and staff might wrongly bill the patient $180 instead of $80 — over-billing the patient by $100 and creating a compliance and trust problem. Accurate posting is what makes every later report trustworthy.

4.6 Participating vs. nonparticipating providers, and secondary-payer math

Whether a provider participates (is in-network) with a payer changes the money materially.

• A participating (par) provider accepts assignment and agrees to the payer's allowed amount as payment in full; the charge-minus-allowed difference is a write-off and cannot be balance-billed.
• A nonparticipating (non-par) provider may not be bound by the same write-off; depending on the payer and law, the patient can owe more. For Medicare, non-par providers who do not accept assignment are subject to a limiting charge cap, so even out-of-network balance billing is restricted.

Secondary-payer math builds on the primary calculation. After the primary pays, the secondary plan considers the remaining patient balance under its rules — it does not simply pay whatever is left, and total payments across plans generally cannot exceed the total allowed.

Worked example — primary then secondary

A service has a primary allowed amount of $200. The patient's primary deductible is met; the primary pays 80%:

• Primary pays: 80% of $200 = $160. Remaining patient balance from primary: 20% of $200 = $40.

Now the secondary plan processes the $40 balance. Suppose the secondary's allowed amount for this service is also $200 and it covers the patient's coinsurance in full:

• Secondary pays the $40 coinsurance. Patient owes $0.

But if the secondary's allowed amount were lower — say $180 — the secondary might pay only up to its allowable after accounting for what the primary already paid. Because the primary already paid $160, and the secondary's allowed is $180, the secondary would pay at most the difference up to its allowable (here $180 − $160 = $20), potentially leaving the patient a small balance depending on plan rules. The exam-level takeaway: the secondary considers the balance under its own allowable — it does not blindly pay the entire remaining amount.

4.7 More reimbursement drills

Drill 5 — deductible not yet met, small service. Allowed $150, remaining deductible $500 (nowhere near met), coinsurance 20%.

• The allowed amount ($150) is entirely applied to the deductible because the deductible ($500) is larger than the service. Patient owes $150; plan pays $0. Coinsurance never comes into play because the deductible is not yet satisfied. (The patient's remaining deductible drops to $500 − $150 = $350.)

Drill 6 — out-of-pocket maximum reached. A patient has already paid $8,000 in cost-sharing this year, and the plan's out-of-pocket maximum is $8,000. A new covered, in-network service has an allowed amount of $400 with normal 20% coinsurance.

• Because the out-of-pocket maximum is met, the plan pays 100% of covered, in-network services for the rest of the period. Patient owes $0; plan pays $400. The coinsurance is waived not by generosity but by the cap.

Drill 7 — copay only. A plan charges a flat $40 copay for an office visit, with the visit's allowed amount at $130 and the deductible not applicable to office visits.

• Patient owes the $40 copay. The plan pays $130 − $40 = $90. A copay is a fixed patient share; the percentage-based coinsurance logic does not apply.

Drill 8 — RVU with a different conversion factor. A service is 3.0 fully adjusted RVUs. Compute payment at two conversion factors: at $32.00, payment = 3.0 × $32.00 = $96.00; at $34.50, payment = 3.0 × $34.50 = $103.50. The $2.50 CF change raises this one service by $7.50 — and every physician service scales the same way, which is why the annual conversion-factor announcement matters to a whole practice's revenue.