What is UB-04 Occurrence Code (Form Locators 31–34)? Definition, Formula, and Benchmark

UB-04 occurrence codes are two-character codes in Form Locators 31 through 34 (with up to 8 occurrence code-date pairs on the UB-04) identifying specific dated events or circumstances related to the claim. Each occurrence code is paired with a date in Form Locators 31–34 (occurrence codes) and the corresponding date in the accompanying "Occurrence Date" field. The code-date pairing allows the claim to communicate when a specific event occurred that affects payer adjudication, coverage, or benefit determination.

Examples of occurrence codes include: 01 (Auto accident / tort liability), 02 (No-fault insurance involved), 03 (Accident / tort liability), 04 (Accident — employment-related), 05 (Accident / other — no med or liability coverage), 10 (Last menstrual period — used for maternity claims), 11 (Onset of symptoms or illness), 17 (Date of outpatient hospice election), 22 (Date active care ended), 27 (Date home health plan established), 40 (Scheduled date of admission), 44 (Date treatment started for physical therapy), 45 (Date treatment started for occupational therapy), 47 (Date cost outlier status begins), 55 (Date discharged to Medicare-certified inpatient or SNF), and others spanning coverage, accident, treatment, and care-transition scenarios.

Unlike condition codes (which identify circumstances without dates), occurrence codes always require accompanying dates. This distinction matters because payer adjudication often depends on specific dates — for example, accident date affects liability coordination; hospice election date affects Medicare hospice benefit activation; treatment start date affects timely filing and benefit year determination.

Occurrence span codes (reported in Form Locators 35–36 on the UB-04) are a related but distinct data element. They identify events with from-and-to dates, such as hospitalization spans, therapy spans, or continuous treatment periods. Occurrence span codes complement occurrence codes for date-range events.

For RCM operations, occurrence code assignment requires accurate dating from clinical and administrative sources. Auto accident date is captured at registration from patient interview; LMP date is captured in maternity workflows; therapy start date comes from the clinical treatment record. HIS and patient accounting systems map common occurrence scenarios to automated occurrence code application; less-common scenarios require manual coding.

Denial and rejection patterns related to occurrence codes include missing occurrence codes when required (e.g., accident claim without accident date), inconsistent dates (occurrence code date conflicting with service dates), and incorrect code-date pairing. Payer companion guides specify required occurrence codes for defined scenarios; compliance requires careful attention to these requirements. Retrospective audit of occurrence code accuracy is important for complex-claim scenarios where manual occurrence coding is common — accident cases, multi-payer coordination, long-term care transitions, and therapy claims.