A system and method for predicting the effect of patient self-care actions on a disease control parameter. A future disease control parameter value X(t.sub.j) at time t.sub.j is determined from a prior disease control parameter value X(t.sub.i) at time t.sub.i based on an optimal control parameter value R(t.sub.j) at time t.sub.j, the difference between the prior disease control parameter value X(t.sub.i) and an optimal control parameter value R(t.sub.i) at time t.sub.i, and a set of differentials between patient self-care parameters having patient self-care values S.sub.M(t.sub.i) at time t.sub.i and optimal self-care parameters having optimal self-care values O.sub.M(t.sub.i) at time t.sub.i. The differentials are multiplied by corresponding scaling factors K.sub.M. The system includes an input device for entering the patient self-care values S.sub.M(t.sub.i). A memory stores the optimal control parameter values R(t.sub.i) and R(t.sub.j), the prior disease control parameter value X(t.sub.i), the optimal self-care values O.sub.M(t.sub.i), and the scaling factors K.sub.M. A processor in communication with the input device and memory calculates the future disease control parameter value X(t.sub.j). A display is connected to the processor to display the future disease control parameter value X(t.sub.j) to a patient.