An infusion system includes a characteristic determining device and an infusion device. The characteristic determining device includes a receptacle for receiving and testing an analyte from the user to determine a concentration of the analyte in the user. The characteristic determining device also includes a communication system for transmitting a communication including data indicative of the determined concentration of the analyte in the user, and the infusion device includes a communication system for receiving the communication from the characteristic determining device. The infusion device further includes a bolus estimator for calculating an estimated amount of fluid to be infused into the body of the user based upon the received data indicative of the determined concentration of the analyte in the user and a target concentration of the analyte in the user, and an indicator to indicate when the estimated amount of fluid to be infused has been calculated.