Accurate bolus insulin doses require calculations based on (1) current blood glucose, (2) target blood glucose, (3) carbohydrate-to-insulin ratios, (4) total grams of carbohydrate in meals, and (5) insulin sensitivity factors. Patients may often forego these calculations for insulin doses based on empirical estimates. A bolus calculator (Medtronic MiniMed) uses these five parameters to generate a recommended bolus insulin dose. This study provides the evidence that a hand-held bolus calculator is effective in controlling postprandial blood glucose. Subjects (n = 49) with Type 1 diabetes and experienced with continuous subcutaneous insulin infusion therapy were randomized to begin one of two bolus dosing methods. After 7 days, subjects crossed over to the alternate method. Prior to entering the Bolus Calculator period, physicians established patients' bolus parameters and programmed them into a personal digital assistant (PDA). Subjects used the PDA to obtain recommended pre-meal insulin bolus doses. During the Standard Bolus period, significantly more correction boluses were administered to curtail postprandial hyperglycemia (p = 0.008) and more supplemental carbohydrate was consumed to raise low blood glucose (p = 0.046). Similar values were observed between the two bolus dosing methods in average deviation of 2-h postprandial blood glucose. Subjects reported that the bolus calculator was easy to use and that they were confident in the bolus doses suggested by the device. These results confirm that bolus insulin doses computed by a bolus calculator, compared with standard bolus techniques, achieve target postprandial blood glucose but with fewer correction boluses and supplemental carbohydrate. A bolus calculator, which can be integrated into insulin pump software, may help patients to more accurately meet prandial insulin dosage requirements, improve postprandial glycemic excursions, and achieve optimal glycemic control.