The field experiments were conducted at the Agricultural Research Station, Dharwad Farm during 2010-11 and 2011-12. The pooled data of crop loss estimation and optimization of spray schedule for Alternaria leaf spot disease in Bt cotton revealed that propiconazole (0.1%) at 35, 55, 75, 95 and 115 days after sowing (DAS) treatment recorded significantly lowest Alternaria leaf spot per cent disease index (3.78 PDI). Similarly, the significantly maximum yield of 2894.50 kg per ha was recorded in propiconazole (0.1%) at 35, 55, 75, 95 and 115 DAS which was on par with propiconazole (0.1%) at 55, 75, 95 and 115 DAS (2802.72 kg/ha) and propiconazole (0.1%) at 35, 55, 75 and 95 DAS (2691.23 kg/ha), respectively. The maximum per cent avoidable yield loss was recorded in propiconazole (0.1%) at 35, 55, 75, 95, and 115 DAS (32.38%). The results indicated that up to 32.38 per cent reduction in yield was caused by Alternaria leaf spot in Bunny Bt. The economics assessed revealed that the treatment with spray of propiconazole (0.1%) at 35, 55, 75, 95 and 115 DAS recorded highest net returns (` 73168 ha-1) and highest BC ratio (1.72).