A computer-implemented method for creating an option on a TBA mortgage backed security, including determining an option position is marked to market daily, where the option position is long or short, determining the option position increased in value by an increased amount on a given day and adding the increased value to a customer's margin account, determining the option position decreased in value by a decreased amount on the given day and subtracting the decreased value from the customer's margin account, and when funds in the margin account are below a predetermined margin requirement, requesting the customer deposit additional funds in the margin account, receiving a request to exercise the option on the TBA mortgage backed security from a customer owning the option on the TBA mortgage backed security.