Overview
The admission hour code 12 is a two-digit code in field 13 of the UB-04 claim form that indicates the patient’s admission or start-of-care occurred between 12:00 PM and 12:59 PM. [1] defines the admission hour code as a number from 00 to 23, representing the hour of admission in military time; code 12 corresponds to the period from 12:00 noon through 12:59 PM. [1] This code is required on inpatient bills only, where field 13 records the date and hour of admission. [1] The MassHealth UB-04 Billing Guide provides general instructions for completing the UB-04 form, including the use of code sets for field-level data, though it does not specify individual hour codes. [2]
When to Use
Use admission hour code 12 when the inpatient admission, start of observation, or start of outpatient care occurs at any time during the 60‑minute block starting at 12:00 PM (noon) and ending at 12:59 PM. [1] This includes admissions that take place exactly at noon (12:00) as well as any minute up to 12:59. Because the code set uses military time, 12 corresponds uniquely to the noon hour; midnight is represented by code 00. [1] When completing field 13 on the UB-04, the provider must enter both the admission date and the two‑digit hour code. This code is mandatory on inpatient claims; outpatient bills may omit the hour if the start‑of‑care time is not required by the payer, but when an hour is required for outpatient services, the same military‑time coding applies. [1] Providers should verify with their specific payer (e.g., Medicare, MassHealth) whether field 13 must include the hour on outpatient claims. [2]
Step-by-Step Claim Example
Scenario: A patient is admitted to the hospital as an inpatient on July 4, 2024, at 12:30 PM. The biller must complete field 13 (Admission/Start of Care Date) with the date and hour.
2. Enter the admission hour code as two digits: 12 (because 12:30 PM falls within 12:00 PM – 12:59 PM). [1]
3. The completed field 13 will display as 0704202412 (date plus hour code). [1]
4. The biller then proceeds to complete the remaining UB-04 fields according to payer instructions (e.g., MassHealth requires electronic submission, but the paper form still uses the same coding conventions). [2]
5. For verification, the biller cross‑references the clock time: 12:30 PM is precisely the 12th hour of the day in military time (12:00 – 12:59). No other code is correct. [1]
6. If the admission had occurred one minute later at 1:00 PM, the code would be 13 (1:00 PM – 1:59 PM). [1]
Common Mistakes & Audit Red Flags
A frequent error is using code 12 for midnight (12:00 AM) instead of code 00. Midnight is 12:00 AM, which is the start of the day and represented by code 00, not 12. [1] Conversely, noon (12:00 PM) is correctly code 12. Another mistake is using code 12 for any time after 12:59 PM; the code must correspond to the exact hour block. [1] Auditors and payers flag claims where the hour code does not align with the documented time in the medical record (e.g., nursing notes, physician orders). [2] A red flag also arises when field 13 shows code 12 but the patient’s stay begins well after 1:00 PM, indicating a data entry error. [1] Providers must ensure that the hour entered matches the actual clock hour; using “12” for any time in the 12:00–12:59 PM block is correct, but using it for any other time is a billing error that can lead to claim rejections or payment recoupment. [1] Additionally, misspacing or entering a single digit (e.g., “2” instead of “02” for 2:00 AM) is invalid; the code must always be two digits. [1] The MassHealth Billing Guide emphasizes that all UB-04 fields must be completed accurately to avoid processing delays. [2]
Related Codes/Fields
| Related Code / Field | Description | Source |
|---|---|---|
| Code 00 | 12:00 AM – 12:59 AM (midnight hour) | [1] |
| Code 11 | 11:00 AM – 11:59 AM | [1] |
| Code 13 | 1:00 PM – 1:59 PM | [1] |
| Code 23 | 11:00 PM – 11:59 PM (last hour) | [1] |
| Field 13 | Admission/Start of Care Date (date + hour code on inpatient bills) | [1] |
| FL 12 (not in source) | Not covered by provided sources | N/A |
| MassHealth UB-04 Guide | General instructions for completing UB-04 field codes | [2] |
Note: All hour codes follow the military‑time scale; code 12 is valid only for the 12:00 PM – 12:59 PM block. [1]
References
[1] CMS R1915CP — https://www.cms.gov/Regulations-and-Guidance/Guidance/Transmittals/downloads/R1915CP.pdf
[2] MassHealth UB-04 Guide — https://www.mass.gov/doc/ub-04-billing-guide-0/download
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Last Updated: 2026-04-26
Sources: CMS Pub. 100-04 Chapter 25, NUBC Official UB-04 Manual, Medicare Contractor Bulletins (Noridian, Palmetto, CGS)