In this study, an Order Level Inventory Model for delayed (non-instantaneous) deteriorating items was constructed. The paper investigated an instantaneous replenishment inventory policy for a non-instantaneous deteriorating item considering time-dependent consumption rate under permissible delay in payments, meaning that, the retailer was allowed a grace period of time to settle for the goods or product supplied to him. In the proposed model, shortages were allowed and fully backlogged. The demand rate before deterioration begin was exponentially declining function of time, while it was constant when deterioration set in, up to when the inventory was completely depleted. The deterioration rate was assumed to be constant throughout the cycle. To determine the optimal order quantity, a solution algorithm was presented. Finally, the model was illustrated with the help of numerical examples. Sensitivity analysis of the optimal solution with respect to various parameters of the system was carried out and the results were discussed in detail

Keywords: Order Level, Inventory, Delayed deterioration, Time dependent declining demand, Shortages, Permissible delay