A medical device for diabetes management, comprising (a) a memory comprising one or more optimal blood glucose values, one or more insulin dose values of a patient, one or more measured blood glucose values, and one or more scaling factors for weighting the impact on a future blood glucose value and that are customizable to an individual patient to predict the effect on the blood glucose of insulin dose actions performed by the individual patient, (b) a microprocessor, in communication with the memory, programmed to calculate a further value, the further value being based on the insulin dose values, the optimal blood glucose values, and the scaling factors, and (c) a display configured to display information according to the further value.