Introduction: Malocclusion, a common dental issue in children, necessitates early intervention to mitigate future orthodontic challenges. Predictive methodologies like Tanaka and Johnston analysis (TJA) and Boston University approach (BUA) aid in mixed and primary dentition analysis for optimal treatment planning. This study aimed to compare TJA and BUA in predicting the mesiodistal width of unerupted permanent canines and premolars and assess gender-based variations. Materials and methods: A cross-sectional study involving 120 children (7–11 years) was conducted at Chettinad Dental College and Research Institute, Chennai, Tamil Nadu, India. Dental models were analyzed using TJA and BUA methods. The mean predicted values of permanent canines and premolars were calculated for both approaches in the upper and lower dental arches. Pearson correlation coefficients were calculated to assess the relationship between TJA and BUA predictions, and statistical significance was determined. Results: Both TJA and BUA exhibited strong positive correlations in predicting dimensions, with slight gender-based variations. TJA predicted values for permanent canines and premolars in the upper arch were 21.13 ± 0.50 and 21.32 ± 0.39, respectively, whereas for BUA, they were 21.45 ± 0.42 and 21.67 ± 0.38, respectively. In the lower arch, TJA predicted values were 20.88 ± 0.63 for canines and premolars combined, while BUA predicted 21.02 ± 0.58. Significant differences were observed only in the upper arch predictions (p = 0.001). Conclusion: Tanaka and Johnston analysis and BUA are valuable in mixed dentition analysis, offering insights into space availability for orthodontic treatment planning. BUA serves as a reliable substitute for TJA when fully erupted permanent incisors are absent, emphasizing the importance of tailored predictive methods in interceptive orthodontics. Model analysis remains pivotal for informed treatment decisions, ensuring optimal dental health outcomes.