In this paper, an interval simulator that considers different sources of uncertainty to estimate the blood glucose level of type 1 diabetes patients is presented. In particular, this study examines a model that includes the dynamics from the insulin delivery input to the subcutaneous-glucose concentration output, and a model that estimates the insulin-on-board considering uncertainty. Each model is studied using modal interval analysis to achieve an optimal computation. The simulator includes several interval models that can be combined with each other in order to expand possibilities in the design and assessment of the glucose regulation algorithms and insulin therapies for diabetes patients. The main features of the interval simulator are shown in this work.