Mild traumatic brain injury (mTBI) frequently presents with persistent symptoms despite normal findings on structural imaging such as MRI or DTI. Existing tools, including the SCAT-5, are primarily designed for acute sideline triage and do not adequately quantify functional impairment or track recovery over time. Building on the published SONOMA-Cognition framework, we introduce SONOMA-Cognition mTBI, a functional assessment system that integrates subjective symptom reporting with objective performance metrics across cognitive, oculomotor, and psychomotor domains. The tool incorporates a standardized 0–3 Functional Severity Scale and calculates percent change values to measure improvement, stability, or decline. SONOMA-Cognition mTBI is designed not as a diagnostic or triage instrument, but as a reproducible method for monitoring functional outcomes, identifying symptom magnification, and guiding treatment progression in mTBI populations. Full administration protocols and proprietary testing forms are not publicly disclosed and are available only to licensed clinical users.