An eminent risk is posed by cognitive biases in trading performance, yet no instrument exists to capture their trading specific manifestations or consequences. This study elaborates on the development and psychometric evaluation of the Cognitive Biases and Re-Trading Tendencies in Day Trading Scale (CBRTT-DT), specifically designed for university student day traders. For the  study we followed a systematic multiphasic approach and generated 43 items from the behavioural finance theories (Prospect Theory, loss aversion and anchoring) and subjected them to expert panel review (N=3), cognitive interviewing (N=10), and pilot testing (N=45). Exploratory factor analysis (N=210) with oblique Promax rotation yielded a refined 17-item structure followed by Confirmatory factor analysis on a different sample (N=210) resulting in a 14-item, parsimonious, 3 factor tool. The final model demonstrated excellent fit (CFI = .908, TLI = .887, SRMR = .069) and strong reliability: Cognitive Biases (8 items, ω = .852, α = .817), Re-Trading Tendencies (3 items, ω = .803, α = .803), Self-Reported Profit/Loss Status (3 items, ω = .822, α = .820), and total scale (ω = .919, α = .869). Average variance extracted values ranged from .415 to .663, confirming convergent validity, while heterotrait-monotrait ratios (.462–.672) supported discriminant validity.