A portable medical monitor system generates a current calibration curve for generating the estimate of the level of an analyte, such as glucose, being monitored. The current calibration curve is based on at least two measured data values of the level being monitored. The system determines a transformation function based on the calibration curve and at least one preceding calibration curve such that the transformation function produces a predictive calibration curve, and generates an estimated level value of the level being monitored, based on sensor output from a sensor associated with the portable medical monitor system, in accordance with the predictive calibration curve.
