Consumer credit products have prevailed for a long time， allowing customers to spend first and pay later， stimulating customers to purchase products. Banks， financial service companies， and e-commerce platforms have all strategically laid out in this industry and provided corresponding online consumer credit services. To further stimulate consumption， companies will offer interest-free consumer credit services. We consider a firm that sells multiple substitutable products and provides interest-free consumer credit services and bears the service costs. We develop an MNL model and incorporate consumer responses to consumer credit services into the model， the firm’s objective is to make the optimal decisions of grace period for each product to maximize the total profit under linear and nonlinear credit service cost structures， respectively. The findings indicate that we can essentially transform the multiple products optimization problem into a single-variable root searching problem， which reduces the calculation complexity. The optimal grace period does not necessarily shrink with the increase of credit service cost and vice versa. Numerical analysis reveals that products with larger profit margins have longer optimal grace periods. We also compare the advantages and disadvantages of the two different credit options， namely， the uniform optimal grace periods for all products （Option 1） and the exclusive optimal grace period for each product （Option 2）. We find that the firm’s total profit from implementing Option 2 is always larger than that from implementing Option 1， especially when the firm’s ability to utilize the sales revenue is not strong， the profit improvement under Option 2 scheme is more significant.