Abstract: A system for the extrapolation of a glucose concentration has a data input device for entering administered insulin doses and their times of administration, a data input device for entering the carbohydrates consumed or to be consumed, a unit for determining an actual glucose concentration at a point in time (ta) in a patient's bodily fluid, a memory unit, and an evaluation unit for evaluation of the data stored in the memory unit, and for the extrapolation of a glucose concentration at a point in time tp, whereby tp is after ta The extrapolation includes determining the portion (Iwirk) of insulin doses that become effective between ta and tp; determining the portion of consumed carbohydrate units KHwirk, that become effective between ta and tp; and determining an extrapolated glucose concentration Gp at the point in time tp with consideration for Iwirk and KHwirk.