1. A medical device for diabetes management, comprising: a memory configured to store (i) a plurality of optimal blood glucose values at a plurality of times, (ii) a plurality of insulin dose values of a patient at said times, (iii) a plurality of predicted blood glucose values at said times, (iv) a plurality of optimal insulin dose values at said times; a microprocessor, in communication with said memory, and programmed to (A) generate a plurality of scaling factors customized to said patient each in response to a change in any one of said insulin dose values at any one of said times and (B) calculate a future blood glucose value based on (i) a plurality of differentials, one of said differentials calculated as one of said scaling factors multiplied by differences between one of said insulin dose values and one of said optimal insulin dose values, (ii) a sum of said differentials plus (iii) a difference between one of said predicted blood glucose values and a corresponding one of said optimal blood glucose values added to said sum of said differentials; and a display configured to display said future blood glucose value.