Aims To determine the optimum combination bolus split to maintain postprandial glycaemia with a high‐fat and high‐protein meal in young people with Type 1 diabetes. Methods A total of 19 young people (mean age 12.9 ± 6.7 years) participated in a randomized, repeated‐measures trial comparing postprandial glycaemic control across six study conditions after a high‐fat and high‐protein meal. A standard bolus and five different combination boluses were delivered over 2 h in the following splits: 70/30 = 70% standard /30% extended bolus; 60/40=60% standard/40% extended bolus; 50/50=50% standard/50% extended bolus; 40/60=40% standard/60% extended bolus; and 30/70=30% standard/70% extended bolus. Insulin dose was determined using the participant's optimized insulin:carbohydrate ratio. Continuous glucose monitoring was used to assess glucose excursions for 6 h after the test meal. Results Standard bolus and combination boluses 70/30 and 60/40 controlled the glucose excursion up to 120 min. From 240 to 300 min after the meal, the glucose area under the curve was significantly lower for combination bolus 30/70 compared with standard bolus (P=0.004). Conclusions High‐fat and high‐protein meals require a ≥60% insulin:carbohydrate ratio as a standard bolus to control the initial postprandial rise. Additional insulin at an insulin:carbohydrate ratio of up to 70% is needed in the extended bolus for a high fat and protein meal to prevent delayed hyperglycaemia. What's new? Combination insulin pump boluses are currently recommended for high‐fat and high‐protein meals; however, there is a paucity of literature comparing combination boluses with a standard bolus for high‐fat, high‐protein meals in children and adolescents with Type 1 diabetes. There are currently no evidence‐based guidelines for determining the optimum split of the combination insulin bolus for children and adolescents with Type 1 diabetes. This is the first study to compare multiple different splits for a combination bolus, incrementally adjusting the percentage of the total insulin dose given in the standard and extended bolus components. This study adds to the literature regarding the optimum split of a combination insulin bolus to control the delayed glycaemic impact of high‐fat and high‐protein meals.