<p>Buy-Now-Pay-Later (BNPL) is a payment item with no-credit-check and instant-approval that allows consumers to make payments in installments over a short period of time. This paper focuses on the inventory problem where the fresh food retailer uses the BNPL installment scheme to make payments, and the number of installments can be flexibly chosen by the retailer. In addition, the demand function for fresh products combines the effects of sale price and product freshness related to the expiration date. The main objective of the retailer is to simultaneously decide on three decision variables (i.e., the number of installments, the sale price, and the replenishment cycle) in order to maximize the total profit. First, we theoretically determine the above optimal decisions and observe that the optimal number of installments is negatively correlated with the interest rate. If the interest rate reaches a critical value, the optimal number of installments is one, and otherwise the optimal number is the maximum number of installments available to the retailer. Then, we give some numerical examples and perform a sensitivity analysis to gain some managerial insights. The results obtained from the numerical examples show that an increase in the interest rate significantly decreases the optimal number of installments and the corresponding total profit, while raising the sale price and extending the replenishment cycle. Additionally, when the product’s shelf life is extended, the sale price, order quantity, replenishment cycle, and overall annual profit all rise initially before falling.</p>