Systems and methods are provided for determining the frequency of a cardiovascular pulse based on a photoplethysmographic measurement of blood in a portion of subsurface vasculature. A plurality of samples of the photoplethysmographic signal are obtained and a frequency spectrum determined based on a first set of the plurality of samples. A frequency is determined based on a maximum frequency component of the frequency spectrum. Further, a confidence level of the determined frequency of the maximum frequency component is determined based on the magnitude of the maximum frequency component and the overall energy in the frequency spectrum. A pulse rate is then determined by updating a predicted pulse rate of a second, earlier set of the plurality of samples based on the frequency of the maximum frequency component and the determined confidence level.
