In this paper, we have proposed an EOQ model under two-level trade credit with installments specially the equal monthly investment (EMI) policies. Installment is a financing arrangement that increases the sales for the business manager and it is very much beneficial for the consumer, specially for the higher value product. Here, the supplier offers a partial credit period M and the retailer offers a permissible delay period N to its customers. The customer pays a fraction α of the amount at the time of purchasing the product and rest (1 − α) by R1 installments within the time N. This study investigates the cases and subcases in details under the conditions N ≤ M and N ≥ M respectively and generalizes some of the literatures such as Soni and Joshi (2013), Mahata and Mahata (2011), Teng (2009) etc when the number of installment is one. We have developed a profit maximization problem on retailer’s inventory model for different cases and subcases. Also, we have shown that the average profit maximizes with installment purchase system than delay-in-payment system and increases with more down payment. Finally, numerical illustrations and its comparative study with the existing methods are performed to justify the novelty of the proposed approach.