UB-04 form locators explained simply: the UB-04 has 81 numbered fields, called form locators (FLs). FL 1 to 41 describe the facility, the patient and the stay. FL 42 to 49 are the charge lines, led by revenue codes. FL 50 to 81 cover payers, insured people, diagnosis and procedure codes, and the physicians responsible for care.
UB-04 form locators 1 to 41: provider, patient and stay details
UB-04 form locators 1 to 41 identify the billing facility, the patient and the shape of the stay or visit. They hold the type of bill, the statement period, admission and discharge details, and the coded facts about the stay: condition codes, occurrence codes and value codes with amounts.
The UB-04 is the institutional claim form, also published by CMS as Form CMS-1450. The National Uniform Billing Committee maintains its data set and describes its Official UB-04 Data Specifications Manual as "the only official source of UB Data." That manual is sold by subscription. Medicare publishes its own instructions for every locator in the Medicare Claims Processing Manual, chapter 25, and the status column in the tables below comes from that chapter. Other payers can set different rules.
All example values in this post come from one fictional inpatient claim. The facility is Example General Hospital, the patient is Riley Sample and the stay runs from March 1 to March 4, 2026. None of it is real.
| FL | Name | Medicare status | Example value (fictional) |
|---|---|---|---|
| 1 | Billing provider name, address, phone | Required | Example General Hospital, Anytown |
| 2 | Pay-to name, address and secondary IDs | Not required; ignored | (blank) |
| 3a | Patient control number | Required | PCN000777 |
| 3b | Medical or health record number | Situational | MRN0000123 |
| 4 | Type of bill | Required | 0111 |
| 5 | Federal tax number | Required | 98-7654321 |
| 6 | Statement covers period, from and through | Required | 030126 030426 |
| 7 | Unlabeled | Not used | (blank) |
| 8 | Patient name and identifier | Required | SAMPLE, RILEY |
| 9 | Patient address | Required | 200 Example Ave, Anytown |
| 10 | Patient birth date | Required | 07141952 |
| 11 | Patient sex | Required | F |
| 12 | Admission or start of care date | Required for inpatient and home health | 030126 |
| 13 | Admission hour | Not required; ignored | (blank) |
| 14 | Priority (type) of admission or visit | Required | (NUBC code) |
| 15 | Point of origin for admission or visit | Required except type of bill 014X | (NUBC code) |
| 16 | Discharge hour | Not required | (blank) |
| 17 | Patient discharge status | Required | (NUBC code) |
| 18 to 28 | Condition codes | Situational | (blank) |
| 29 | Accident state | Not used | (blank) |
| 30 | Unlabeled | Not used | (blank) |
| 31 to 34 | Occurrence codes and dates | Situational | (blank) |
| 35 and 36 | Occurrence span codes and dates | Required for inpatient | (NUBC code and dates) |
| 37 | Unlabeled | Not used | (blank) |
| 38 | Responsible party name and address | Not required | (blank) |
| 39 to 41 | Value codes and amounts | Required | (NUBC code and amount) |
Type of bill in FL 4
FL 4 is a four-digit code that packs three facts after a leading zero. Chapter 25 says the second digit identifies the type of facility, the third classifies the type of care, and the fourth is the "frequency" code, the bill's place in the episode of care. The Medicare Claims Processing Manual, chapter 3 says "inpatient services should be billed on an 11X type of bill." In the example, 0111 is an inpatient hospital bill with frequency 1, which the Medicare Claims Processing Manual, chapter 9 lists as an admit through discharge claim.
Condition, occurrence and value codes
These three code families carry facts that do not fit anywhere else. Condition codes in FL 18 to 28 describe conditions or events that apply to the billing period, entered in numerical order. Occurrence codes in FL 31 to 34 pair a two-character event code with a six-digit date. Occurrence span codes in FL 35 and 36 add a from and a through date. Value codes in FL 39 to 41 pair a code with an amount of up to nine digits, in ascending code order.
Chapter 25 gives one occurrence code example. A patient whose Part A benefits ran out on January 8, 2005 has code A3 and date 010805 in FL 31. The full code lists are in the NUBC manual and from Medicare contractors.
What do UB-04 revenue codes in FL 42 tell a payer?
UB-04 revenue codes in FL 42 tell a payer what kind of charge each line is: a room, a pharmacy charge, a lab test, an emergency room visit. Each code is four digits, and every charge in FL 47 needs one beside it. The HCPCS code in FL 44 then names the specific procedure when one applies.
Chapter 25 says the provider must "enter the appropriate numeric revenue code on the adjacent line in FL 42 to explain each charge in FL 47." Chapter 9 describes it as the "appropriate four-digit numeric revenue code to explain each charge."
Revenue codes come in families written with an x for the last digit. The Medicare manuals use these, among others:
| Revenue code or range | Meaning in the Medicare manuals | Source |
|---|---|---|
| 010x to 021x | Accommodation codes | Chapter 3 |
| 0120 | Semi-private room | Chapter 3 |
| 0250 | Pharmacy | Chapter 3 |
| 0300 to 0319 | Laboratory tests | Chapter 25 |
| 045x | Emergency room services | Chapter 4 |
| 0624 | Investigational device line, with the IDE number in FL 43 | Chapter 25 |
| 0001 | Total of all charges | Chapter 25 |
The Medicare Claims Processing Manual, chapter 4 shows revenue code 0450 on an outpatient line next to HCPCS code 99283. That pairing is the pattern for outpatient bills: the revenue code says which department, and FL 44 says which service.
Chapter 25 sets four rules for revenue codes on the UB-04:
- Revenue codes go in ascending numeric order and should not repeat on the same bill where possible.
- There is no fixed total line. The provider enters revenue code 0001, and its FL 47 amount is the sum of all charges.
- To limit line items, the provider should "sum revenue codes at the 'zero' level to the extent possible."
- On inpatient bills, FL 44 shows the accommodation rate rather than a HCPCS code.
Payers build rules around these codes. Chapter 25 says the patient's reason for visit in FL 70 is required on type of bill 013x and 085x when certain priority codes appear and revenue codes 045x, 0516 or 0762 are reported. A wrong revenue code can change which other locators a payer expects.
UB-04 service line locators 42 to 49
UB-04 service line locators 42 to 49 form the charge area. Each line has a revenue code, a description, a HCPCS code or rate, a service date, units, total charges and non-covered charges. FL 49 is unlabeled. A Medicare UB-04 claim can run to 450 lines across nine pages, according to chapter 25.
| FL | Name | Medicare status | Example line 1 (fictional) | Example line 2 (fictional) | Total line (fictional) |
|---|---|---|---|---|---|
| 42 | Revenue code | Required | 0120 | 0250 | 0001 |
| 43 | Revenue description | Not required | SEMI-PRIVATE ROOM | PHARMACY | TOTAL |
| 44 | HCPCS, accommodation rate or HIPPS code | Required | 1500.00 (rate) | (blank) | (blank) |
| 45 | Service date | Required for outpatient | (blank) | (blank) | (blank) |
| 46 | Service units | Required | 3 | (blank) | (blank) |
| 47 | Total charges | Required | 4500.00 | 820.00 | 5320.00 |
| 48 | Non-covered charges | Required | 0.00 | 0.00 | 0.00 |
| 49 | Unlabeled | Not used | (blank) | (blank) | (blank) |
The example line 1 is three days of a semi-private room at a fictional rate of $1,500.00 a day. Units in FL 46 count days for accommodation codes. Chapter 25 says units generally quantify services by revenue code category, such as days in a type of accommodation, but equal the number of times a procedure was performed when HCPCS codes are required.
FL 45 matters most on outpatient bills. Chapter 25 says hospitals must report a single line item date of service for "every iteration of every revenue code" on outpatient bills. If a service happens five times in the billing period, the revenue code and HCPCS code are entered five times, once per date.
FL 43 is for people. Chapter 25 says the description "assists clerical bill review." It also carries two special uses: the investigational device exemption number for revenue code 0624, and the National Drug Code for Medicaid drug rebates, written as N4 followed by the 11-digit code.
FL 48 holds the non-covered part of each line's charge, and the 0001 line sums it. Reading the service lines from a scanned or faxed UB-04 is covered in how UB-04 OCR reads revenue code service lines.
UB-04 payer, insured and diagnosis locators 50 to 81
UB-04 payer, insured and diagnosis locators 50 to 81 cover who pays, who holds the coverage and why the patient was treated. FL 50 to 65 hold up to three payers on lines A to C. FL 66 to 75 hold diagnosis and procedure codes. FL 76 to 79 name physicians, and FL 80 and 81 add remarks and codes.
| FL | Name | Medicare status | Example value (fictional) |
|---|---|---|---|
| 50 | Payer name, lines A to C | A required; B and C situational | Example Health Plan |
| 51 | Health plan ID | A required; B and C situational | (plan number) |
| 52 | Release of information indicator | Required | Y |
| 53 | Assignment of benefits indicator | Not used | (blank) |
| 54 | Prior payments | Situational | (blank) |
| 55 | Estimated amount due from patient | Not required | (blank) |
| 56 | Billing provider NPI | Required | 1987654328 |
| 57 | Other provider ID | Not used | (blank) |
| 58 | Insured's name | Required | SAMPLE, RILEY |
| 59 | Patient's relationship to insured | Required | (NUBC code) |
| 60 | Insured's unique ID | A required; B and C situational | XJH000333444 |
| 61 | Insurance group name | Situational | (blank) |
| 62 | Insurance group number | Situational | (blank) |
| 63 | Treatment authorization code | Situational | AUTH00098765 |
| 64 | Document control number | Situational | (blank) |
| 65 | Employer name of the insured | Situational | (blank) |
| 66 | Diagnosis and procedure code qualifier | Required | 0 |
| 67 | Principal diagnosis code | Required | J189 |
| 67A to 67Q | Other diagnosis codes | Situational | A: I10 |
| 68 | Reserved | Not used | (blank) |
| 69 | Admitting diagnosis | Required for inpatient claims subject to QIO review | J189 |
| 70a to 70c | Patient's reason for visit | Situational | (blank) |
| 71 | Prospective payment system code | Not used | (blank) |
| 72 | External cause of injury codes | Not used | (blank) |
| 73 | Reserved | Not used | (blank) |
| 74 | Principal procedure code and date | Situational, inpatient only | (blank) |
| 74a to 74e | Other procedure codes and dates | Situational, inpatient only | (blank) |
| 75 | Reserved | Not used | (blank) |
| 76 | Attending provider name and IDs | Situational | 1234567893, EXAMPLE, MORGAN |
| 77 | Operating provider name and IDs | Situational | (blank) |
| 78 and 79 | Other provider name and IDs | Situational | (blank) |
| 80 | Remarks | Situational | (blank) |
| 81 | Code-code field | Situational | (blank) |
The example diagnosis codes are real ICD-10-CM codes, listed by the NLM Clinical Tables ICD-10-CM search as J18.9, pneumonia, unspecified organism, and I10, essential (primary) hypertension. They are entered without the decimal, which chapter 25 calls "implied". They show the layout, not how to code a stay.
Diagnosis fields
FL 66 is the ICD version, 0 for the tenth revision. FL 67 is the principal diagnosis, which chapter 25 defines as "the condition established after study to be chiefly responsible for this admission." Chapter 25 says the code must be complete and may not be padded with zeros. FL 67A to 67Q add up to 17 other diagnoses, and each diagnosis field has room for a present on admission indicator. Unlike the professional claim, the UB-04 has no pointers tying a line to a diagnosis. That link on the CMS-1500 is explained in the guide to diagnosis pointers on the CMS 1500.
Provider fields
FL 56 is the billing NPI. FL 76 names the attending provider, the person with "overall responsibility for the patient's medical care and treatment." FL 77 names the operating provider when a surgical procedure is on the claim. FL 78 and 79 take a qualifier such as DN for a referring provider. Each provider field also allows a secondary ID with qualifiers 0B, 1G or G2. How these numbers line up with the professional form is covered in the guide to NPI and tax ID fields on claim forms.
Which UB-04 form locators do payers reject most often?
Medicare's manuals do not rank UB-04 form locators by how often payers reject them. What chapter 25 does publish is which locators are required and how they must be filled. Those locators, led by type of bill, statement dates, revenue codes and totals, the billing NPI and the principal diagnosis, are the first ones to check.
Medicare's chapter 25 makes these locators carry the most rules:
- FL 4, type of bill. Required. Every later rule depends on it. The outpatient line-date rule, for example, applies to a list of bill types, and the reason-for-visit rule applies to 013x and 085x.
- FL 6, statement covers period. Required. Discharge status in FL 17 is reported "as of the 'Through' date" in FL 6, so the two must agree.
- FL 42 and FL 47, revenue codes and charges. Required. Each charge needs a revenue code, and the 0001 line must hold the sum.
- FL 45, service dates on outpatient bills. Each repeat of a revenue code needs its own date.
- FL 56, billing NPI. Required since May 23, 2008.
- FL 66 and FL 67, ICD version and principal diagnosis. Required. The version digit must match the codes, and the principal diagnosis must be the full code.
- FL 69, admitting diagnosis. Required for inpatient claims subject to QIO review.
The Medicare Claims Processing Manual, chapter 26 gives the general consequence on the professional side: claims with incomplete or invalid information "may be returned to the submitter as unprocessable." When a payer processes a claim but pays less, the reasons arrive as adjustment codes on the remittance. The guide to the CARCs billing teams see most often covers how to read them.
Before any of this, the facility must be using the right form at all. The guide to who files a CMS 1500 claim and who files a UB-04 claim covers that choice.
UB-04 locators left unlabeled or reserved for national use
Several UB-04 locators are unlabeled or reserved: FL 7, 30, 37, 49, 68, 73 and 75. Medicare's chapter 25 marks each one "not used", and for most of them adds that data entered there will be ignored. A few labeled locators, such as FL 29, 53, 57, 71 and 72, are also unused by Medicare even though they have names.
The blank fields fall into three groups for a Medicare claim:
- Unlabeled or reserved, not used: FL 7, 30, 37, 49, 68, 73 and 75. The chapter 25 layout still gives them space, such as two lines of 12 and 13 characters for FL 30.
- Labeled, but not used by Medicare: FL 29 accident state, FL 53 assignment of benefits, FL 57 other provider ID, FL 71 prospective payment system code and FL 72 external cause of injury codes.
- Labeled, but not required by Medicare: FL 2 pay-to details, FL 13 admission hour, FL 16 discharge hour, FL 38 responsible party and FL 55 estimated amount due.
Two practical points follow. Chapter 25 says data in a "not used" locator is ignored, so nothing the payer needs should be placed there. And a non-Medicare payer may use these fields, so a blank FL 29 that suits Medicare may not suit an auto or liability payer. The NUBC manual and each payer's billing guide govern those cases.
One field is open by design. FL 81, the code-code field, lets a provider report "additional codes related to a Form Locator" or codes from an external list approved by the NUBC. It holds a qualifier, a code and a value on each of four lines.
The note under FL 49 in chapter 25 adds one more instruction. It says "PAGE ____ OF ____" and the creation date on line 23 should appear on every page of the UB-04, which helps when a multi-page claim arrives out of order.
Keying a UB-04 by hand means copying dozens of short codes exactly. Schema Care pulls UB-04 fields and codes out as structured data with a confidence score per field, and a reviewer handles only the fields below the threshold you set. The review workflow on the homepage walks through each step.