Background: Venous thromboembolism (VTE) is a serious complication in patients with moderate to severe traumatic brain injury (TBI). While early VTE prophylaxis (VTEp) initiation (24–72 hours) has been shown to reduce thromboembolic events without increasing hemorrhagic complications, the safety and efficacy of very early (? 24 hours) administration remain unclear. This study examines the impact of VTEp timing on intensive care length of stay (ICU LOS) in TBI patients, stratified by bleeding risk using the modified Berne-Norwood Criteria (mBNC). Objective: To develop predictive tools for robust risk stratification that incorporate TBI characteristics, VTEp timing, and patient factors to predict rebleeding risk and optimize ICU resource utilization. Methods: A retrospective cohort study was conducted using the ACS-TQIP-PUF (2017–2021) database. Adult patients (?15 years) with isolated TBI receiving VTEp (low molecular weight heparin, unfractionated heparin, or mechanical filter) were included. Patients were categorized by mBNC re-bleeding risk (low, moderate, high) and VTEp timing (very early ? 24 hours, middle > 24 to < 72 hours, late ? 72 hours). ICU LOS was analyzed using multivariable linear regression models. Results: Among 99,078 patients, very early VTEp was associated with significantly shorter ICU LOS in low and moderate-risk groups (3.7–4.4 days reduction, p < .01) compared to late initiation. High-risk patients receiving very early VTE PPX exhibited increased mortality (p < .01). Patients with and without anticoagulation history showed similar trends. Conclusion: Very early VTEp significantly reduces ICU LOS in low/moderate risk TBI patients without increasing complications. This finding highlights the importance of timely VTEp in minimizing ICU resource utilization without increasing rebleeding risk in appropriately stratified patients. Developing predictive tools that integrate TBI size, type, and patient factors can further refine risk stratification and optimize clinical decision-making for VTE management in TBI patients. Levels of Evidence: Level III, retrospective/epidemiological Highlights 1. Initiating VTE prophylaxis within 24 hours significantly decreased ICU length of stay in low and moderate-risk TBI patients. 2. Early VTE prophylaxis was beneficial for most patients, high-risk TBI patients experienced increased mortality with very early administration. 3. Patients with and without a history of anticoagulation or bleeding disorder showed similar trends in ICU stay reduction with very early VTEp.