UB04 Admission Hour Code 23: 11:00 PM - 11:59 PM

Overview

Admission Hour Code 23 on the UB-04 claim form corresponds to the time interval 11:00 PM to 11:59 PM (military time 23). This code is entered in Field 13 – Admission/Start of Care Date, which is required on inpatient bills (and also used for outpatient start of care) ^[1]. The admission hour is represented as a two‑digit numeric code from 00 (midnight) through 23 (11:00 PM), following the 24‑hour clock. Code 23 is the final valid code in the sequence, covering the last hour of the day before midnight. The UB‑04 form is a standard institutional claim format used by hospitals and other facilities; its completion guidelines, including code sets, are detailed in payer‑specific manuals such as the MassHealth UB‑04 Billing Guide ^[2]. Accurate reporting of the admission hour is essential for claims processing, utilization review, and compliance with Medicare and other payer rules.

When to Use

Code 23 must be used when the patient’s admission (for inpatient stays) or start of care (for outpatient services) occurs at any time between 11:00 PM and 11:59 PM on the date recorded in Field 13 ^[1]. Because the code represents a full hour block, it applies regardless of the exact minute (e.g., 11:05 PM, 11:30 PM, 11:59 PM). This code is part of the required set of admission hour codes that must be reported on all inpatient bills; outpatient claims may also require it when the start of care date is captured ^[1]. Providers should note that Code 23 is not used for 12:00 AM (midnight) – that is Code 00 – nor for any time prior to 11:00 PM (e.g., 10:00 PM would be Code 22). Correct assignment ensures the admission hour aligns with the patient’s documented arrival time and prevents billing inconsistencies. Reference materials, such as the MassHealth UB‑04 Billing Guide, reiterate the importance of using official code sets for the admission hour field ^[2].

Step‑by‑Step Claim Example

Scenario: A patient is admitted to the hospital on March 5, 2024, at 11:30 PM.

1. Field 13 – Admission/Start of Care Date: Enter the date of admission as 03/05/2024 (MM/DD/YYYY). ^[1]
2. Admission Hour (military time): Because the patient arrived at 11:30 PM (within the 11:00 PM – 11:59 PM block), use code 23. ^[1]
3. Placement on the UB‑04: The date and hour are combined in Field 13 (e.g., “03052024 23” or as specified by the billing software).
4. Supporting Documentation: The patient’s registration system must record an arrival time of 23:30 to support the code. ^[2] (general recordkeeping expectation)
5. Claim Submission: The completed UB‑04 is submitted electronically (per MassHealth policy) or on paper if an exemption applies. ^[2]

This example demonstrates the direct correspondence between clock time and admission hour code.

Common Mistakes & Audit Red Flags

• Using 23 instead of 00 for midnight: Code 00 is for 12:00 AM, not 11:59 PM. A common error is reporting 23 for a patient admitted at 12:00 AM, which should be 00. ^[1]
• Misreading AM/PM: Confusing 11:00 PM (23) with 11:00 AM (11) leads to wrong hour codes. Auditors flag this when the admission hour does not match the documented time in the medical record.
• Omitting the hour code entirely: Field 13 requires a date and hour; omitting the hour can cause claim rejection or processing delays. Payer guides stress completing all required fields ^[2].
• Inconsistent time zones: If the facility uses a time zone different from the payer’s standard, the code may be incorrect. Always use the local facility time as documented at admission.
• Audit red flag: A history of using Code 23 for admissions that occur very close to midnight can trigger review for potential upcoding of length‑of‑stay or improper discharge timing.
• Failure to update when admission time changes: If a patient is admitted at 11:45 PM but the recorded time is later corrected to 12:05 AM (Code 00), the claim must be amended.

Related Codes/Fields

Field or Code	Description	Source
Field 13 – Date	Admission/Start of Care Date (MM/DD/YYYY)	[1]
Code 00	12:00 AM – 12:59 AM	[1]
Code 22	10:00 PM – 10:59 PM	[1]
Code 23	11:00 PM – 11:59 PM (this code)	[1]
Field 14 – Priority (Type) of Admission	Admission type code (e.g., 1 = Emergency)	[1] (referenced elsewhere)
Field 15 – Source of Admission	Point of origin code (e.g., 1 = Physician referral)	[1] (referenced elsewhere)

The admission hour code (00–23) is one element of the overall admission date field. All codes follow the military time schema as defined by CMS and implemented in the UB‑04 claims standard.

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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