How to Read a UB-04 Hospital Bill Line by Line (2026)

What exactly is a UB-04, and why should you care about it?

The UB-04 claim form, officially known as the CMS-1450, is the standardized claim form used by hospitals, skilled nursing facilities, home health agencies, and other institutional providers to submit claims for services rendered. When you get a hospital bill, the summary you receive in the mail is typically a condensed patient statement — but the UB-04 is the full, line-by-line claim the hospital sends to your insurer. Those two documents don't always match, and the discrepancies are where overcharges hide.

The UB-04 (formally CMS-1450) and the CMS-1500 are the two standard paper claim forms for medical billing in the United States, used by virtually all providers and payers under HIPAA Transaction and Code Set Standards (45 CFR Part 162). While the CMS-1500 is used for professional claims like a physician's office visit, the UB-04 is designed for the complex nature of facility billing. That means if you had surgery, your surgeon may bill separately on a CMS-1500, while the hospital bills the operating room, nursing care, supplies, and medications on a UB-04.

You have the right to see this document. You have a federal legal right to request and receive a copy of your UB-04 hospital claim form. This isn't a courtesy your hospital extends to you — it's a protected right under the Health Insurance Portability and Accountability Act (HIPAA). Specifically, the rule that protects you is 45 CFR § 164.524, and it applies to every hospital, clinic, and healthcare facility in the United States. When you call the hospital's billing department, ask specifically for the "UB-04 claim form" or "CMS-1450" — using vague terms like "my bill" often routes you to the summary statement instead. You can also compare the UB-04 against your Medicare Summary Notice or commercial Explanation of Benefits (EOB), which differ significantly in how they display the same underlying claim data.

The stakes are real. According to CMS, the Medicare Fee-for-Service estimated improper payment rate was 6.55%, or $28.83 billion, in FY 2025. That figure represents claims that were paid at the wrong amount — and a portion of those errors show up directly in the revenue code lines of a UB-04.

How is the UB-04 structured?

The UB-04 form, also known as the CMS-1450 claim form, is structured to support the complex billing and reimbursement requirements of institutional healthcare facilities. Organized into 81 form locator boxes, the UB-04 captures institutional billing information such as admission details, patient status codes, revenue codes, occurrence codes, condition codes, diagnosis codes, discharge disposition, payer information, and facility charges required for institutional claims processing.

Think of the form in three zones. The top third (roughly FL 1–41) covers administrative and demographic data — who you are, who the provider is, and the dates and circumstances of your visit. The middle section (FL 42–49) is the revenue code table, where every charged service is listed line by line. The bottom third (FL 50–81) covers payer information, insurance details, diagnosis codes, and the attending physician's National Provider Identifier (NPI). Billing errors can appear in any zone, but the revenue code table is where dollar-value mistakes are most common.

Developed and maintained by the National Uniform Billing Committee (NUBC) and adopted by the Centers for Medicare & Medicaid Services (CMS), the UB-04 replaced the older UB-92 form to standardize facility-based medical billing across the U.S. healthcare system. It is the basic form prescribed by CMS for the Medicare program and is only accepted from institutional providers that are excluded from the mandatory electronic claims submission requirements set forth in the Administrative Simplification Compliance Act, Pub.L. 107-105, and the implementing regulation at 42 CFR § 424.32. Most hospitals actually submit claims electronically in the 837I EDI format, but the UB-04 is the human-readable reference that maps directly to it.

What do the header fields (FL 1–41) tell you?

The top section of the UB-04 establishes the "who, where, and when" of your claim. Here are the fields that matter most to patients checking for errors:

FL 1 — Provider Name and Address. This should match the hospital or facility where you were actually treated. If the name listed is a parent health system entity rather than the specific facility, that's not necessarily an error, but flag it if the address is completely wrong.

FL 4 — Type of Bill (TOB). The TOB is a four-digit code (usually beginning with a leading zero) that appears in FL 4. It tells the payer what kind of facility is billing and what the frequency of the claim is. The first digit indicates the facility type (hospital, SNF, clinic); the second identifies the care type such as inpatient or outpatient; and the third states the bill frequency — original, corrective, or final. For example, a Type of Bill code of 131 is an outpatient hospital claim, and 111 is an inpatient hospital claim. If you were treated as an outpatient but the TOB shows inpatient, that's a serious error with significant cost implications. See our guide on the billing difference between observation and inpatient admission, which can cost you thousands.

FL 6 — Statement Covers Period. This is the "from" and "through" date of the bill. Every service date listed in the revenue code section (FL 45) must fall within this range. If the Statement Covers Period doesn't match the revenue line dates in FL 45, that's a flag for incorrect billing and can trigger an audit.

FL 17 — Patient Discharge Status. Medicare relies heavily on this code. A code of "01" (discharged home) when the patient actually went to a skilled nursing facility (code "03") can lead to a Recovery Audit Contractor (RAC) audit down the line. For patients, this matters because the discharge status affects what post-acute care Medicare covers.

FL 31–34 — Occurrence Codes and Dates. These two-digit codes describe significant events related to your stay — an accident, a covered Medicare spell of illness, or a prior authorization date. Missing occurrence codes can cause a claim to underpay your insurer on your behalf, which may affect how much the payer credits toward your deductible.

How do you read the revenue code lines (FL 42–49)?

This is the heart of the UB-04 for error-spotting purposes. Revenue codes are three- or four-digit codes used on UB-04 claim forms to identify specific accommodation, ancillary, and other service categories provided during a hospital stay. Every line item on a hospital claim must have a revenue code. Each row in this section represents a category of charges — a room-and-board day, a lab test, a drug, a surgical supply.

Here's what each column in the revenue code section means:

• FL 42 — Revenue Code. Unlike CPT codes, which describe specific procedures, revenue codes describe the department or service category. For example, 0300–0309 = laboratory, 0360 = operating room, 0450 = emergency room, 0636 = pharmacy (drugs requiring detailed coding). CMS requires revenue codes in Form Locator 42 to explain each charge line.
• FL 43 — Revenue Description. The provider enters a narrative description or standard abbreviation for each revenue code shown in FL 42 on the adjacent line in FL 43. The information assists clerical bill review, and descriptions or abbreviations correspond to the revenue codes.
• FL 44 — HCPCS/CPT Code. Revenue codes identify the service category (where/what type), while CPT or HCPCS codes identify the specific procedure or service performed. On most outpatient claims, both are required. The revenue code tells the payer which department performed the service; the CPT/HCPCS code tells them exactly what was done.
• FL 45 — Service Date. The date the specific service was delivered. Cross-reference this against your discharge paperwork, any lab or imaging results, and your EOB to confirm the service actually occurred on that date.
• FL 46 — Units of Service. The quantity billed — number of hours, days, tablets, or procedures. A common billing error is inflated units (e.g., billing 2 units of a procedure performed only once). This is also where to catch phantom charges for services you never received.
• FL 47 — Total Charges. The gross billed amount for that line (units × rate). This is NOT what you owe — it's the starting number before insurance adjustments and contractual discounts.
• FL 48 — Non-Covered Charges. Charges the payer has flagged as not covered under your plan. Review these carefully — items incorrectly placed here can shift costs to you that your plan should cover.

The last revenue code entered in FL 42 is "0001," which represents the grand total of all charges billed. That grand total in FL 47 on the "0001" line is what your insurer received as the full billed amount. If it's significantly higher than what your summary statement shows, dig into the individual revenue lines.

According to OIG reports, overbilling or inconsistent code usage — including incorrect revenue codes — has led to investigations and repayment demands. Revenue codes like 0300 (laboratory) and 0450 (emergency services) are frequently audited due to their volume and potential for overlap with observation or same-day surgical services. If you see both 0450 (ER) and 0762 (observation) on a claim for the same date, that's a pattern worth questioning — you can check the adjustments section of your bill to see if the insurer already caught and reduced a duplicate charge.

What do the diagnosis and physician fields (FL 67–81) tell you?

FL 67 — Principal Diagnosis Code. ICD-10 diagnosis codes go in FL 67 (principal diagnosis) and FL 67A–Q (other diagnoses). The form must also include the Present on Admission (POA) indicator for each diagnosis. The principal diagnosis drives the Diagnosis-Related Group (DRG) assignment for inpatient claims, which in turn determines the flat payment amount Medicare sends the hospital. An incorrect principal diagnosis can inflate that DRG payment — a practice known as upcoding. Our dedicated guide covers how upcoding works and how to spot it on your bill.

FL 76 — Attending Physician NPI. This field lists the National Provider Identifier of the physician who supervised your care. A discrepancy between the NPI on the claim and the NPI on file with the credentialing department at the payer is one of the most significant reasons for a UB-04 denial. For Medicare claims, the attending physician in FL 76 must be a qualified individual who is appropriately affiliated with the facility in the PECOS system. As a patient, you can look up any NPI for free at the CMS NPPES registry to verify the physician listed actually treated you.

FL 80 — Remarks. Hospitals use this free-text field to explain unusual circumstances, coordination of benefits situations, or prior authorization details. If your claim was denied, check here for explanations that may support — or contradict — the insurer's reason for denial.

What are the most common UB-04 billing errors to flag?

The table below summarizes the highest-risk form locators for patient-facing billing errors, drawn from CMS billing guidance and HHS OIG audit patterns. Use it as a checklist when reviewing your own UB-04.

How do you actually dispute a line you believe is wrong?

Start by getting both the UB-04 and an itemized bill simultaneously. To get a UB-04 from a hospital, contact the Patient Financial Services or Billing Department directly and specifically request the "UB-04 claim form copy" or "CMS-1450 print" for your specific date of service. Provide your full name, date of birth, account number, and dates of service. Most hospitals deliver the form within 5 to 10 business days under HIPAA 45 CFR § 164.524 access rights. If you're also covered by Medicare, you can obtain a copy from your Medicare Administrative Contractor (MAC). The difference between an itemized statement and a summary statement is significant — always request both.

Once you have the UB-04, work through it systematically. Compare FL 45 (service dates) to your hospital bracelet records or discharge paperwork. Check FL 46 (units) against nursing notes or pharmacy records you can request under HIPAA. Look up any CPT code in FL 44 you don't recognize using the CMS HCPCS lookup tool. If you find a charge that doesn't match a service you received, that's a potential phantom charge — document it in writing and submit a formal dispute to both the hospital's billing department and your insurer.

For insured patients, your insurer's claims team can also request the 837I electronic equivalent of the UB-04 directly from the hospital. If the hospital disputes your correction, ask your insurer to open a formal claim review. A 2024 HHS Inspector General audit found that 37% of hospitals failed to fully comply with CMS price transparency requirements three years after the rule took effect — meaning many hospitals still don't publicly publish the rates you'd need to independently verify FL 47 charges. If you're self-pay or underinsured, you may have separate rights under charity care rules. Our full guide on uninsured patient discounts and charity care covers what hospitals are required to offer.

If your dispute involves a surprise bill from an out-of-network provider at an in-network facility — a situation that often originates in a UB-04 with an unexpected NPI in FL 78 or FL 79 (Other Providers) — you may have rights under the No Surprises Act and the federal independent dispute resolution process.

About VerifyDoc: We help patients identify errors and overcharges on medical bills. We publish guides on hospital billing, the No Surprises Act, and disputing medical charges, updated as federal and state rules change.