Online retail sites vary in terms of payment processes that consumers encounter. Little is known about how different implementations of payment processes affect consumers. Through the lens of mental accounting research, we theorize and empirically find that implementation characteristics of usability, feedback, and rehearsal affect consumer recall of past expenses and future impulse purchase decisions. The results have implications in terms of the design of new payment systems, especially with regard to the interface that a consumer encounters in online shopping. The study, by highlighting the influence of online payment processes on consumer behavior, also raises the possibility of using payment systems as strategic differentiators in a competitive environment.