A method may include delivering insulin, using an insulin pump and a controller, over a first diurnal time period based on a baseline basal insulin rate stored in memory. The controller may receive blood glucose data to control delivery of insulin via the insulin pump in amounts variable from the baseline basal insulin rate to control blood glucose levels for a person with diabetes (PWD). The method may also include modifying the baseline basal insulin rate stored in the memory for a second diurnal time period that is at least 20 hours after the first diurnal period based on an amount of insulin actually delivered during the first diurnal time period.
