Abstract: A software platform implementing a payment plan option for customers purchasing goods and services from a merchant website has an intuitive and transparent customer experience. The customer is able to calibrate down payment, frequency, and duration of the payment plan using user interface elements that show all values and periods being adjusted as the customer is making modifications to the payment plan. The platform allows the merchant to offer payment plans where customers can pay on specific days of the month. Customers can change payment plan terms after the plan has been agreed to and memorialized in a plan agreement containing the payment schedule. When terms have been changed, a replacement agreement is created and replaces the prior agreement. A plan can have automatic scheduled payments or manual payments. For manual payments, the merchant is able to select multiple manual plans for which he wants payments made and submit the batch of manual payments in parallel or concurrently.