There are three hierarchical steps to fill the yield gaps in agricultural systems. These steps are determination of potential yield, yield gaps and system optimization to fill yield gaps. In this study a simple mechanistic model was developed and tested to determine potential yield and yield gaps of Cumin (Cuminum cyminum) in nine regions of Khorasan provinces (including Bojnourd, Qaeen, Mashhad, Neishabour, Sabzewar, Gonabad, Ferdous, Kashmar and Birjand). Collected data of related year from 228 fields were used to calculate yield gaps. Results indicated variable potential yields in different climatic conditions (the areas with cooler climate and higher radiation had higher potential yields). Also, yield gaps varied considerably between regions (from 2.42 ton.ha-1 in Bojnourd to 0.68 ton.ha-1 in Sabzewar). The highest value for potential yield belonged to Bojnourd (3.7 ton.ha-1). The collected data from studied fields and sensitivity analysis on sowing date (based on common sowing dates range) showed that inappropriate sowing dates was one of the most important yield reducing factors in all regions. Results revealed that if the yield gaps can be filled based on appropriate management option, yield can be increased by two to three folds in some regions