An apparatus and method are provided for determining a patient's carbohydrate to insulin ratio (CIR) and insulin sensitivity factor (ISF), and using these values, along with values for current blood glucose level and deviation from target blood glucose level, for determining insulin dose in view of carbohydrate intake during a particular time period. The apparatus and method employ algorithms that can be implemented in any of a personal computer, personal data assistant, hand held computing device, blood glucose monitor, infusion pump, medication delivery pen, meter, calculator, among other therapeutic, diagnostic or informational devices used for managing a patient's blood glucose levels.