The basic EOQ model is depends on the subsequent assumption:
1) The forecast usage or demand for a specified period, usually one year, is identified
2) The usage/demand is even during that period
3) Inventory orders can be replenished immediately because there is no delay in placing and receiving orders.
There are two distinguishable costs related with inventories: costs of demanding and costs of carrying.
Figure 1 demonstrates a graph illustrating the behaviour of the carrying cost, the ordering cost and the total of these two costs. The carrying cost varies directly along with the order size as the average level of inventory is one-half of the order size, while the ordering cost varies inversely along with the order size.