This paper develops an overtime production model for demand rate to be a function of price and stock-level. Companies manufacturing rate fluctuates with the change in stock-level and demand rate. To control the deterioration up to some extent, the system introduces preservation technology investment. The article permits a two-level credit policy for flexible financing. The model calculates feasible profit value under preservation technology investment, production period and selling price.  Conclusively, a sensitivity analysis related to different inventory parameters is performed to study the dependency of optimal values on parameters.