Chitosan is an eco-friendly polysaccharide, enhancing growth and managing disease infections in fruits and vegetables. This study examines the effects of preharvest application of chitosan and calcium (Ca) on yield and postharvest chitosan coating on tomato storage. There were nine preharvest treatments, viz., T0 = control, T1 = 50 ppm chitosan, T2 = 80 ppm chitosan, T3 = 0.50% Ca, T4 = 1.0% Ca, T5 = T1 and T3 (combined), T6 = T2 and T3 (combined), T7 = T1 and T4 (combined), and T8 = T2 and T4 (combined), and three postharvest treatments, viz., C0 = control, C1 = 0.10% chitosan, and C2 = 0.20% chitosan, to examine the yield parameters and major physical and biochemical qualities of tomatoes on different days after postharvest storage (DAPS). The results revealed that chitosan and Ca treatments had a significant influence on yield while showing an insignificant impact on the biochemical qualities of fresh-harvested tomatoes. Postharvest application of chitosan coatings effectively reduced weight loss and shrinkage (34–37%) compared to the control. At 20 DAPS, only the 0.20% solution met the marketable threshold of ≥5.0, while the control failed in 100% of the samples. As storage duration increased, titratable acid and vitamin C decreased, while lycopene and sugar content rose in tomatoes. This research indicates that foliar spraying with 80 ppm chitosan during fruit initiation significantly boosts tomato yield, and a 0.20% chitosan coating on postharvest tomatoes enhances longevity and preserves biochemical quality.