The present invention relates to a controller unit and methods for controlling an insulin pump. The controller unit 100 includes a user input 104 that receives a gain factor. The gain factor has been calculated based on historical data in relation to a patient. The controller unit includes a measurement input 106 for receiving data representative of a measured blood glucose level for the patient. Processing logic 108 of the controller unit is configured to apply the measured blood glucose level to a pancreatic beta-cell insulin secretion computational model to predict an insulin output level, apply the gain factor to the predicted insulin output level to determine a patient insulin deficiency level, and calculate a control signal for controlling the insulin output level of the insulin pump based on the patient insulin deficiency level. Methods are provided for optimising the gain factor based on the historical data in relation to the patient.
