In this paper, two different rates of production problem of production inventory system for deteriorative items having constant demand, linear demand as well as quadratic demand is considered and in order to cut costs, it is preferable to begin production at a low rate (X1) and gradually increase to a higher rate (X2) over time. This is because starting with a low rate of production prevents an excessive quantity of manufactured goods from being stored at the outset. There will be three models created: constant demand in the first model, linear demand in the second model, and quadratic demand in the third model. Mathematical model is constructed for every model, as well as ideal manufacturing lot size is then determined in order to reduce overall costs. Worked-out example are provided that we then validate quantitatively. Microsoft Visual Basic 6.0 was used to write the code for this model's outcome validation.