The present invention extends to methods, systems, and computing system program products for iteratively calculating autocorrelation function for streamed data in real time by iteratively calculating one or more components of autocorrelation function. Embodiments of the invention include iteratively calculating one or more components of autocorrelation function at a specified range of lags in an adjusted computation window based on the one or more components of the autocorrelation function at the specified range of lags calculated for a previous computation window and then calculating the autocorrelation function at the specified range of lags using the iteratively calculated components. Iteratively calculating autocorrelation function avoids visiting all data elements in the adjusted computation window and performing redundant computations thereby increasing calculation efficiency, saving computing resources and reducing computing system's power consumption.