During composting, nitrogen loss primarily occurs in the form of ammonia, which negatively affects the quality of organic fertilizers, because nitrogen is a crucial macronutrient for plant growth. Additives are often employed to mitigate these losses, particularly when composted waste contains high nitrogen levels. This study aims to assess the effectiveness of biochar and crude glycerin as additives in the composting of fish waste in static windrows. Based on fresh weight, five treatments were evaluated: control (no additive), 5 and 10% biochar, and 5 and 10% crude glycerin, over three time periods (50, 70, and 90 days of composting). A 3:1 (mass/mass) ratio of fish waste to bulking agent was used, and the mixture was placed in nylon bags to enhance additive assessment. Thermophilic temperatures were achieved during the early stages of composting and after turning. There were no significant differences (