A computer implemented method for estimating manufacturing target bias for products in manufacturing tools. The method first establishes a first data set according to manufacturing target bias history based on a correlation with tools used. The manufacturing tools comprise a first manufacturing tool and other manufacturing tools. Next, a testing operation is executed for a predicted product in the first manufacturing tool to obtain a first predicted manufacturing target bias. Finally, manufacturing target bias of the predicted product in the other manufacturing tools is calculated according to the first data set and the first predicted manufacturing target bias.