UB04 Admission Hour Code 00: 12:00 Midnight - 12:59 AM

Overview

Code 00 on the UB‑04 admission hour field (FL 13) represents the time period 12:00 Midnight – 12:59 AM. The admission hour is always reported in military (24‑hour) format, with codes ranging from 00 (midnight) through 23 (11 PM). ^[1] specifies that “the admission hour code (00‑23) represents the hour of admission in military time” and defines Code 00 = 12:00 AM (midnight). The UB‑04 field itself, required only on inpatient bills, captures the date and hour when the patient was admitted for inpatient care or when outpatient care began. ^[1] This code is the starting point of the day and must be entered as two digits (e.g., “00”) to comply with the UB‑04 format.

When to Use

Code 00 is used when the patient’s admission hour falls at any point between 12:00 AM (midnight) and 12:59 AM on the admission date. For example, if a patient is formally admitted at 12:00 AM, 12:15 AM, or 12:30 AM, the correct admission hour code is 00. ^[1] It is critical to remember that the code represents the entire hour, not just the exact minute of entry. Therefore, any admission occurring within the 00:00–00:59 window requires code 00. ^[1] This code applies exclusively to inpatient claims; outpatient start‑of‑care dates may also use FL 13, but the hour code remains mandatory for inpatient stays. Do not use code 00 for admissions after 1:00 AM (code 01) or for noon (code 12). ^[1]

Step-by-Step Claim Example

Scenario: A patient is admitted for inpatient care on January 15, 2025, with the admission time recorded as 12:15 AM.

Step 1 – Locate FL 13 on the UB‑04 form. This box is titled “Admission/Start of Care Date” and appears near the top of the form. ^[1]

Step 2 – Enter the admission date in the format MMDDYYYY (e.g., 01152025). ^[2] (The MassHealth guide confirms the UB‑04 date format, though the CMS transmittal also implies a date‑hour combination.)

Step 3 – Enter the admission hour code directly after (or in the adjacent hour field, depending on payer layout). For 12:15 AM, the hour code is 00. Write “00” as two digits. ^[1]

Step 4 – Verify the complete entry reads as:
01152025 00 (date followed by hour code). This tells the payer that the patient was admitted on January 15, 2025, during the midnight hour.

Step 5 – Submit the claim electronically (most payers require electronic submission). ^[2] notes that MassHealth mandates electronic claims unless an exemption is granted.

Common Mistakes & Audit Red Flags

• Using 24 instead of 00: 24:00 is not a valid code. The military‑time scale uses 00–23, so midnight must be coded as 00. ^[1]
• Omitting the leading zero: Writing “0” instead of “00” can cause the field to be misread as a single digit, leading to claim rejection or audit flags. Always provide two digits. ^[1]
• Confusing midnight with noon: Noon is 12:00 PM, which corresponds to code 12, not 00. Using code 00 for a noon admission is a frequent error. ^[1]
• Applying code 00 to outpatient claims when not required: While FL 13 appears on all UB‑04 forms, the admission hour is specifically mandated only for inpatient bills. Submitting an outpatient claim with a 00 hour code may raise unnecessary questions. ^[1]
• Using code 00 for admissions after 00:59: If the patient is admitted at 1:00 AM or later, the correct code is 01. Always round down to the hour of the admission, not the preceding hour. ^[1]

Related Codes/Fields

Code	Meaning (Military Time)	AM/PM Equivalent
00	00:00 – 00:59	12:00 AM – 12:59 AM
01	01:00 – 01:59	1:00 AM – 1:59 AM
12	12:00 – 12:59	12:00 PM – 12:59 PM
23	23:00 – 23:59	11:00 PM – 11:59 PM

All codes in the admission hour field follow the 00‑23 military‑time pattern. ^[1] The field is part of FL 13 on the UB‑04 form, which also requires the date of admission for inpatient bills. ^[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