Purpose: Despite widespread adoption of open abdominal management (OAM), there is currently no threshold criterion for OAM duration for non-trauma patients. Moreover, there is a positive relationship between morbidity and the duration of OAM, but an uncertain relationship with patients’ age. Therefore, a novel clinical index for the duration of open abdominal management (IDOM) was developed based on the patient’s age and risk of severe complications following OAM to indicate the maximum tolerable number of days of OAM based on the individual’s age. The utility of this new index was evaluated. Methods: This retrospective study included 65 non-trauma patients managed with an open abdomen (OA) from August 2015 to August 2018. The IDOM was developed based on the patient’s age. The result indicated the maximum number of OA days. Patients’ demographic and operative variables were examined and patient data was assigned to one of two groups according to whether the actual number of OA days was above or below the calculated IDOM. Prevalence of complications between these groups was compared. Measures of validity were employed to assess the utility of the IDOM for patient complications. Results: Sixty-five patients were included. The above-the calculated IDOM group exhibited a significantly longer OA and higher rates of wound complications and postoperative respiratory complications compared with the below the calculated IDOM group. The IDOM predicted the incidence of OA-related complications with a sensitivity of 72.4%, and a specificity of 80.6%. Conclusion The IDOM is a potentially useful tool for appropriate duration at the outset of OA.